CrystEngComm Dynamic Article LinksC Cite this: DOI: … · Lucia Carlucci,* Gianfranco Ciani, Davide M. Proserpio and Marco Visconti Received 4th May 2011, Accepted 6th July 2011

Dynamic Article LinksC<CrystEngComm

Cite this: DOI: 10.1039/c1ce05520h

www.rsc.org/crystengcomm PAPER

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The novel metalloligand [Fe(bppd)3] (bppd ¼ 1,3-bis(4-pyridyl)-1,3-propanedionate) for the crystal engineering of heterometallic coordinationnetworks with different silver salts. Anionic control of the structures†

Lucia Carlucci,* Gianfranco Ciani, Davide M. Proserpio and Marco Visconti

Received 4th May 2011, Accepted 6th July 2011

DOI: 10.1039/c1ce05520h

The crystal engineering of heterometallic coordination networks based on the novel tris-chelate

metalloligand [FeIII(bppd)3] (bppd ¼ 1,3-bis(4-pyridyl)-1,3-propanedionate) is reported here. The

building block [Fe(bppd)3] crystallizes with a balanced packing of the D and L forms and exhibits

distorted octahedral chiral structure with six exo-oriented pyridyl donor groups suitable for networking

via interactions with external metal ions. It was reacted with many silver salts AgX (X ¼ BF4�, ClO4

�,

PF6�, AsF6

�, SbF6�, NO3

�, CF3SO3�, tosylate) giving polymeric products with structures depending

on the nature of the counter-anions X�. With pseudo-spherical anions (such as BF4�, ClO4

�, PF6�,

AsF6� and SbF6

�) 2D polymeric species [Fe(bppd)3Ag](X) are obtained showing sql topology, because

the metalloligands use only four, out of the six pyridyl donors, to bind silver ions. The reaction with Ag

(CF3SO3) affords a quite different type of [Fe(bppd)3Ag]+ 2D polymeric frame, with the metalloligands

that again employ only four pyridyl groups for networking, i.e. a double layered species comprised of

two superimposed honeycomb sheets, exhibiting a (43.63) topology. By using AgNO3 a 3D framework,

[Fe2(bppd)6Ag3](NO3)3, is obtained that, interestingly, consists of double layers like those of the

previous species connected via Ag bridges on both sides to produce a binodal 5,4-connected 2-fold

interpenetrated network. The reaction with silver p-toluenesulfonate produces the complex 3D

nanoporous network [Fe3(bppd)9Ag5](tosylate)5 with 6-connected metalloligands and 3- and

4-connected silver ions. An interesting rationalization of this network is that it is comprised of 1D

parallel nanotubular motifs of hexagonal section with square-meshed walls; these nanotubes are

laterally interconnected by Ag triple-bridging atoms to generate the whole 3D array.We observe that in

these species the metalloligands use a variable number of pyridyl donors for networking, i.e. four, five

and six, leading to frames of increased complexity and dimensionality that are strongly dependent on

the anionic shape and nature. The reactions of the analogous metalloligand [AlIII(bppd)3] with the same

AgX salts under similar conditions produce polycrystalline materials that in the cases of silver triflate

and tosylate are isostructural with the corresponding iron containing species, as evidenced by their

X-ray powder diffraction spectra.

Introduction

A great interest is currently focused on the design of coordina-

tion networks/metal–organic frameworks (MOFs)1,2 because

they are promising materials for many potential applications

such as gas storage, molecular sensing, separation, ion exchange,

Universit�a degli Studi di Milano, Dipartimento di Chimica Strutturale eStereochimica Inorganica, Via G. Venezian 21, 20133 Milano, Italy.E-mail: [email protected]; Fax: +390250314454; Tel:+390250314446

† Electronic supplementary information (ESI) available. CCDCreference numbers 824472–824473 and 824475–824478. For ESI andcrystallographic data in CIF or other electronic format see DOI:10.1039/c1ce05520h

This journal is ª The Royal Society of Chemistry 2011

catalysis, optics and magnetism.2 A useful strategy to the rational

synthesis of such networked compounds consists in the use of

molecular building blocks, in particular those called metal-

loligands,3–6 that contain suitably oriented exo-donor groups and

are therefore able to direct, in principle, the formation of desired

polymeric architectures.

The metalloligands can be employed in place of organic

ligands to join different metal centers, thus possibly affording

heterobimetallic architectures, which can display novel proper-

ties; at difference from the SBUs that can be envisaged as

fundamental units in the networks assembled via the reticular

chemistry approach1b,c,7 the metalloligands are self-existing

entities. The stepwise approach implies a careful choice of

polyfunctional ligands for the preparation of the discrete

CrystEngComm

http://dx.doi.org/10.1039/c1ce05520h






Table 1 List of the products and their structural type

No. Compound Structural motifs

1a0 [Fe(bppd)3]$xSolv Tris-chelate metalloligand2a–e [Fe(bppd)3Ag](X)

X ¼ BF4�, ClO4

�, PF6�,

AsF6�, SbF6

�

2D (4,4) sql, undulated layers

3a [Fe(bppd)3Ag](CF3SO3) 2D double layers,polythreaded system

4 [Fe2(bppd)6Ag3](NO3)3 3D 4,5-connected, 2-foldinterpenetrated

5a [Fe3(bppd)9Ag5](tosylate)5 3D single trinodal net3,4,6-connected

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metal–organic building blocks with a rather rigid and defined

stereochemistry. Chelating ligands are frequently employed,

which must bear additional outward oriented donor groups,

mainly carboxylate, nitrile or pyridyl groups. A number of

metalloligands have been employed for this purpose; for

instance, tris(dipyrrinato) metal complexes5 were shown to be

a versatile class of metalloligands for the preparation of a variety

of interesting MOFs. Functionalised b-diketonato ligands were

used as suitable chelating agents for the preparation of metal-

loligands, both tris-chelated6a,b and bis-chelated6c,d complexes.

In this concern we have already investigated the use of ad hoc

prepared metalloligands for the engineering of heterometallic

networks, such as the complex trans-[Ru(pyrazine)4Cl2] showing

four equatorial pyrazine donors,3h ZnII-metalated pyridyl-func-

tionalised porphyrins,3o and the tris-chelate species [MIIIL3] [M¼Fe3+ and Co3+] and [MIIL3]

� [M ¼ Mn2+, Co2+, Zn2+, Cd2+] with

HL ¼ 1,3-bis(4-cyano-phenyl)-1,3-propanedione.8

We report here the synthesis and characterization of the novel

tris-chelate metalloligand [Fe(bppd)3] (with Hbppd ¼ 1,3-bis(4-

pyridyl)-1,3-propanedione) and it use for the modular engi-

neering of heterometallic MOFs with a variety of AgX salts

(X� ¼ BF4�, ClO4

�, PF6�, AsF6

�, SbF6�, NO3

�, CF3SO3�,

tosylate). The b-diketonato ligand (Hbppd, see Scheme 1),

besides acting as a chelating agent on the FeIII center, can donate

the 4-pyridyl groups to external metals. The [Fe(bppd)3] metal-

loligand has thus six exo-donor groups with an approximate

octahedral orientation. In the networking process a variable

number of pyridyl donors are employed, i.e. four, five and six,

giving frameworks of increasing complexity and dimensionality

that have been structurally characterized (see Table 1); the

dependence of the framework structures on the counter-anions

has been investigated. This bppd ligand seems to be particularly

suitable in the preparation of chelate metalloligands for the

assembly of networks but in spite of this, curiously, it has been

used only very recently in this concern: the complex

[Gd(bppd)3(H2O)] that forms a 1D linear chain structure9 has

been described in 2009 and, during the preparation of this paper,

a communication has appeared10 reporting the Group 13 met-

alloligands [M(bppd)3] (M ¼ Al3+ or Ga3+) together with the

mixed-metal frameworks obtained by reaction with silver salts.

We describe here also the reactions of [Al(bppd)3] with the same

AgX salts employed with the analogous Fe(III) metalloligand.

Experimental

General procedures

All the commercial reagents and solvents employed (Sigma-

Aldrich) were of high-grade purity and used as supplied, without

further purification. All manipulations were performed under

aerobic conditions unless standard Schlenk techniques were

required. Anhydrous tetrahydrofuran was freshly distilled under

Scheme 1

CrystEngComm

nitrogen from sodium/benzophenone. NMR spectra were

recorded on Bruker AC300 or AC400 instruments; d values are

given in ppm relative to tetramethylsilane. Infrared spectra were

collected on a Perkin-Elmer Paragon 1000 FT-IR spectrometer

equipped with an i-series FT-IR microscope. Thermogravimetric

analysis (TGA) was performed on a Perkin-Elmer TGA 7

instrument under dynamic nitrogen flow (20 cm3 min�1). A ramp

rate of 10 �Cmin�1 in the temperature range 20–700 �C was used.

The purity of all synthesized compounds was checked by X-ray

powder diffraction analyses. Powder patterns were recorded on

a Philips PW1820 diffractometer (Cu Ka radiation, l ¼1.5405 �A), in the 5–35� 2q range (0.02� and 2.5 s per step).

Magnetic susceptibilities (cM) were determined at room

temperature using a MSB-AUTO (Sherwood Scientific Ltd.)

magnetic balance. Three measurements for every sample (50–

100 mg) were performed. Diamagnetic corrections were esti-

mated from Pascal’s constants.

Synthesis

1,3-Bis(4-pyridyl)-1,3-propanedione (Hbppd). 4-Acetylpyridine

(3.0042 g, 24.80 mmol) was added under nitrogen to NaH (60%

dispersion in mineral oil, 2.0075 g, 50.1 mmol) and anhydrous

THF (7 mL). A solution of ethyl isonicotinate (7.5007 g, 49.6

mmol) in THF (8 mL) was then added dropwise in about 20 min

under continuous stirring (exothermic reaction). The mixture

was heated at 65 �C for 1 h and 40 minutes under nitrogen flux.

After quenching, by addition of iced water (about 40 mL), the

pH was adjusted to neutrality with glacial acetic acid. From the

neutral mixture the ligand Hbppd precipitated as a whitish solid,

which was recovered by filtration, washed with water and dried

in air (yield 71%). IR (KBr) nmax/cm�1 3548w, 3482w, 3414m,

3092w, 3034m, 1616vs, 1586vs, 1546vs, 1492vs, 1460sh, 1406s,

1274m, 1238s, 1214s, 1056s, 992m, 936w, 902w, 844m, 786vs,

704m, 684m, 606vs, 494m, 466m. 1H NMR (300 MHz, acetone-

d6) d 7.46 (1H, s, COCHCO), 8.03 (4H, d, J 6.14 Hz, py), 8.84

(4H, d, J 6.14 Hz, py).

Tris[1,3-bis(4-pyridyl)-1,3-propanedionate]iron(III) (1a). To

13 mL of 0.2 M NaOH Hbppd (502.2 mg, 2.22 mmol), partially

dissolved in 50 mL of water, was added. After slow addition of

12 mL of an aqueous solution of FeCl3$6H2O (200.0 mg,

0.74 mmol) a red solid precipitated immediately. The mixture

was left to stir for 3 h, then it was filtered to give compound 1a as

a red solid which was washed with water (2 mL) and dried in air

(yield: 0.520 g, 96%). Magnetic susceptibility (296 K) 5.352(5)



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BM. Red needle crystals suitable for X-ray analysis were

obtained from 6 � 10�4 M THF solution (10 mL) by slow

evaporation at room temperature in about 10 days. IR (KBr)

nmax/cm�1 3042m, 2964m, 2926w, 1586vs, 1522vs, 1488vs,

1418vs, 1386vs, 1368sh, 1320s, 1296s, 1220m, 1060s, 944m, 850s,

782s, 716m, 694s, 664vw, 620s, 534m, 474m.

Tris[1,3-bis(4-pyridyl)-1,3-propanedionate]aluminium(III) (1b).

Compound 1b was obtained as a microcrystalline white powder

following the procedure described for 1a using AlCl3 as a source

of aluminium. Yield 99%. IR (KBr) nmax/cm�1 3041m, 1591vs,

1532vs, 1487vs, 1440vs, 1419vs, 1387vs, 1331s, 1311s, 1225m,

1084m, 1064s, 993w, 953m, 850m, 781s, 721m, 702m, 665w, 632s,

590m, 557m, 533m, 482w, 424m. 1H NMR (400 MHz, DMSO-

d6) d 7.49 (1H, s, COCHCO), 8.02 (4H, d, J 6.26 Hz, py), 8.78

(4H, d, J 6.26 Hz, py).

[FeIII(bppd)3Ag]X$4THF (X ¼ BF4�, ClO4

�, PF6�, AsF6

�,

SbF6�) (2a–e). Compounds 2a–e were obtained by similar

procedures using the proper silver salt. The synthesis of 2c is

described here as a representative example: a CH3CN solution

(10 mL) of AgPF6 (34.7 mg, 0.137 mmol) was added drop by

drop, through a drop funnel, to compound 1a (100.1 mg,

0.137 mmol) dissolved in THF (10 mL). On leaving the mixture

to stir overnight compound 2c precipitated as a red solid which

was collected on a B€uchner funnel by filtration, washed with

THF and dried in air. Yield 66.7%.

IR (KBr) nmax/cm�1 3650m, 3460b, 3112m, 3043m, 2972m,

1576vs, 1520vs, 1419vs, 1359vs, 1304s, 1223m, 1080s, 1061vs,

946m, 880s, 831vs, 794vs, 719s, 702s, 623s, 557s, 477s.

Compound 2a: yield 27.3%, IR (KBr) nmax/cm�1 3103m,

3043m, 1579vs, 1528vs, 1486vs, 1421vs, 1385vs, 1318s, 1302vs,

1223s, 1060vs, 944m, 849m, 784s, 718m, 698s, 622s.

Compound 2b: yield 76.3%, IR (KBr) nmax/cm�1 3384b,

3104m, 3046m, 1576vs, 1520vs, 1486vs, 1418vs, 1362vs, 1318vs,

1302vs, 1223m, 1099vs, 1061vs, 944m, 849m, 785s, 718m, 698s,

623s, 543s, 476s.

Compound 2d: yield 68.8%, IR (KBr) nmax/cm�1 3368b,

3116m, 3044m, 1579vs, 1523vs, 1486vs, 1420vs, 1385vs, 1367s,

1318s, 1302s, 1223m, 1078w, 1062s, 1002w, 945m, 850m, 786s,

700vs, 622s, 542m, 476m.

Compound 2e: yield 71.6% IR (KBr) nmax/cm�1 3417b, 3111m,

3047m, 2975w, 2929w, 1578vs, 1526vs, 1487vs, 1421vs, 1387vs,

1318m, 1304s, 1225m, 1062s, 945m, 851m, 793s, 718m, 700m,

659s, 623s, 546m, 477m.

Crystals of 2a–e suitable for X-ray analyses were obtained by

slow diffusion of 9 � 10�4 M CH3CN solutions (4 mL) of the

proper silver salt into 9 � 10�4 M THF solutions (4 mL) of 1a in

about 5 days. Identical species were obtained also using different

Ag/ML stoichiometric ratios.

Derivatives of the aluminium species 1b with silver perchlorate

and silver hexafluorophosphate were prepared with the same

procedure but, due to poor crystallinity of the bulk materials, it

was not possible to ascertain their nature.

[M(bppd)3Ag]CF3SO3 [M ¼ Fe(III) (3a), Al(III) (3b)].

Compounds 3a and 3b were obtained by similar procedures on

using proper reagents. Only the synthesis of 3a is described here

in detail. A water solution (10 mL) of AgCF3SO3 (19.2 mg,


0.0747 mmol) was slowly added (in about 30 min) through a drop

funnel to compound 1a (53.6 mg, 0.0733 mmol) dissolved in

EtOH (10 mL). The mixture was left under stirring for 16 h to

allow the complete precipitation of 3a as a red solid. The red solid

was collected on a B€uchner funnel by filtration, washed with

EtOH and dried in air (yield 44.5%). Samples of compound 3a,

showing lower crystallinity, have also been obtained using

CH3CN solution of AgCF3SO3 and THF solution of 1a (yield

62%). IR (KBr) nmax/cm�1 3410b, 3114m, 3046m, 1578vs, 1522vs,

1486vs, 1420vs, 1385vs, 1367sh, 1319s, 1302vs, 1278s, 1259s,

1225s, 1162s, 1062s, 1031s, 945m, 850s, 785s, 718m, 697s, 664w,

638s, 622s, 541m, 476m.

Compound 3b: polycrystalline product: yield 54%. IR (KBr)

nmax/cm�1 3437b, 3118m, 3049m, 1590s, 1534vs, 1488s, 1439vs,

1421s, 1386vs, 1312s, 1276s, 1258s, 1225s, 1163s, 1063s, 1031s,

952m, 851m, 783m, 721m, 705m, 638s, 559m, 534m, 483w, 421w.

Crystals of 3a suitable for X-ray analyses were obtained by

slow diffusion of a 9 � 10�4 M ethanolic solution (4 mL) of 1a

into a 1.8 � 10�3 M aqueous solution (4 mL) of AgCF3SO3 in

about 10 days.

[FeIII2(bppd)6Ag3](NO3)3 (4). A solution of AgNO3 (19.3 mg,

0.114 mmol) in H2O (10 mL) was slowly added (in about 10 min)

to compound 1a (54.2 mg, 0.0741 mmol) dissolved in EtOH

(10 mL). The mixture was left under stirring for 16 h. The red

solid was collected on a B€uchner funnel by filtration, washed

with EtOH and dried in air to obtain pure 4 (yield 81%). Samples

of compound 4, showing lower crystallinity, have also been

obtained using CH3CN solution of AgNO3 and THF solution of

1a (yield 83%). IR (KBr) nmax/cm�1 3418b, 3111, 3044m, 1578vs,

1523vs, 1486vs, 1420vs, 1384vs, 1364sh, 1318s, 1303vs, 1223s,

1062s, 944m, 849m, 785s, 718m, 698m, 664w, 622s, 543s, 477m.

Crystals of 4 suitable for X-ray analysis were obtained by slow

diffusion of a 9 � 10�4 M ethanolic solution of 1a into a 2.7 �10�3 M aqueous solution of AgNO3 (4 mL) in about 10 days.

[M3(bppd)9Ag5](tosylate)5 [M ¼ Fe(III) (5a), Al(III) (5b)].

Compounds 5a and 5b were obtained by similar procedures on

reacting respectively 1a and 1b with silver tosylate. Only the

synthesis of 5a is described here in detail. A solution of Ag

(tosylate) (62.7 mg, 0.2246 mmol) in CH3CN (10 mL) was slowly

added (in about 30 min) through a drop funnel to a solution of

compound 1a (98.3 mg, 0.1344 mmol) dissolved in THF (10 mL).

The mixture was left under stirring for 22 h to allow the complete

precipitation of 5a as a red solid. The red solid was collected on

a B€uchner funnel by filtration, washed with EtOH and dried in

air to give pure 5a (yield 30.7%). IR nmax/cm�1 3421b, 3041m,

2920m, 1578vs, 1519vs, 1486vs, 1418vs, 1384vs, 1366vs, 1318s,

1302vs, 1216s, 1191s, 1126s, 1062s, 1037s, 1012s, 944m, 848s,

784s, 718m, 694s, 665w, 621s, 569s, 541s, 476m.

Compound 5b: polycrystalline product: yield: 98%. IR (KBr)

nmax/cm�1 3421b, 3039w, 2919w, 1590s, 1534vs, 1487s, 1439vs,

1420s, 1387s, 1331m, 1312s, 1211s, 1191s, 1129s, 1064m, 1042m,

1013m, 953m, 850w, 815w, 783m, 722m, 666w, 692s, 633m,

570m, 560sh, 534m, 483m, 423m.

Red hexagonal prismatic crystals of 5a suitable for X-ray

analysis were obtained by slow diffusion of a 8 � 10�4 M THF

solution of 1a into a 2.4 � 10�3 M CH3CN solution of Ag

(tosylate) (4 mL) in about 4 days.

CrystEngComm


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Transformation of 3 to 4. Procedure A: 7.9 mg (0.007 mmol) of

ground crystals of 3awere added to a solution of AgNO3 (1.6 mg,

0.009 mmol) and NaNO3 (1.3 mg, 0.015 mmol) in EtOH/water

(1 : 1) (4 mL). The mixture was left to stand for 15 days at room

temperature. The red solid was then collected on a Hirsch funnel

by filtration, washed with EtOH and dried in air to give pure 4x

(6.5 mg).

Procedure B: 13.3 mg (0.004 mmol) of ground crystals of 3a

were added to a solution of AgNO3 (2.5 mg, 0.015 mmol) in

EtOH/water (1 : 1) (4 mL). The mixture was left to stand for

15 days at room temperature. Then the red solid was collected on

a Hirsch funnel by filtration, washed with EtOH and dried in air

to give pure 4y (12.7 mg).

Thermogravimetric analyses (TGA)

The analyses were performed on compounds 1a, 2a–d, 3a, 4 and

5a. They show a weight loss of about 5% in the range 20–160 �C(1a), 2–3% in the range 20–100 �C (2a, 2b), 5% in the range 20–

170 �C (2c, 2d), 5% in the range 20–70 �C (3a, 4), 5% in the range

20–110 (5a) due to de-solvation processes. Compound 1a is

stable up to 250 �C, while network decomposition of 2a, 2b, 3a, 4

and 5a starts at different temperatures depending on the nature

of the polymers (range 200–230 �C).

Crystallography

Data were collected on a Bruker APEXII-CCD diffractometer

using MoKa radiation (l ¼ 0.71073 �A). Empirical absorption

corrections (SADABS)11 were applied to all data. The structures

were solved by direct methods (SIR97)12 and refined by full-

matrix least squares on F2 (SHELX-97)13 using the WINGX

interface.14 All hydrogen atoms were placed in geometrically

calculated positions and subsequently refined using a riding

model with Uiso(H) ¼ 1.2 Ueq(C) (Table 2). The accessible free

voids were calculated by PLATON.15 Full details of the refine-

ments can be found in the cif file (under refine_special_details

keyword). Crystals of all monomers and polymers are unstable in

air and were kept under mineral oil and collected at low

temperature (150 K for all but 120 K for 5a). Compound 1a was

collected at room temperature and any attempt to find other

crystals to re-collect it at low temperature was unsuccessful. All

tested crystals of 1a, 2a, 3a, 4 and 5a also showed weak

diffraction, hence resulting in high R values. Excluding 3a and

5a, anisotropic thermal parameters were assigned to all non-

hydrogen atoms, except for clathrate THF molecules (in 2a, 2b),

disordered anions or parts of ligands (in 2a, 2c, 4). In the extreme

cases of compounds 3a and 5a, due to the poor diffraction (and

a strong decay of 31% for 3) of all the sampled crystals, only the

heaviest atoms were refined with anisotropic thermal parameters,

so as to allow a reasonable parameter/observation ratio and

result in an acceptable structural model. For the same reason

some groups were refined as rigid body: the anions in 2a, 2b and

one triflate in 3a. Furthermore all structures of 1a, 3a, 4 and 5a

were found to contain disordered solvents (such as tetrahydro-

furan, ethanol, acetonitrile and water). Since it was difficult to

refine a consistent model for the solvents, their contribution was

subtracted from the observed structure factors according to the

BYPASS16 procedure, as implemented in PLATON with the

CrystEngComm

command SQUEEZE. Topological analyses were performed

with TOPOS.17

Results and discussion

The [Fe(bppd)3] metalloligand

The synthesis of 1,3-bis(4-pyridyl)-1,3-propanedione (Hbppd)

was carried out according to a literature method, using a base-

catalyzed condensation between 4-acetylpyridine and ethyl

isonicotinate.

The tris-chelate [Fe(bppd)3] (1a) metalloligand was obtained in

good yields by mixing water solutions of Hbppd, NaOH and

FeCl3$6H2O under stirring for 3 h. Slow evaporation of a THF

solution of the crude bulk product afforded red needle-like

crystals suitable for X-ray analysis, of formula [Fe(bppd)3]$

xSolv (1a0). The structure of 1a0 has been determined by X-ray

diffraction since it seemed to be a potentially useful chiral

building block for networking. Moreover, magnetic measure-

ments at RT show that it is a high-spin d5 species that can be used

to introduce magnetic centers in a polymeric network.

The crystal structure of 1a0 consists of chiral tris-chelate

complexes with rather distorted octahedral geometry around the

metal center. The asymmetric unit comprises an entire complex

in a general position [complex A, containing Fe(1)], and another

half one [complex B, containing Fe(2)], with the metal atom

placed in a special position on a 2-fold axis (Wyckoff c position).

Complexes A and B are chemically equivalent but crystallo-

graphically distinct. Two adjacent independent complexes,A and

B, exhibiting opposite conformation (L and D), are shown in

Fig. 1.

The coordination polyhedra of both complexes are similar,

with an irregular octahedral geometry. The Fe–O bond lengths

are in the range 1.945(8)–2.007(6) �A for Fe(1) and 1.975(5)–2.019

(6)�A for Fe(2), and the bite angles O–Fe–O are in the ranges 87.2

(3)–87.4(3)� [with Fe(1)] and 86.1(2)–87.2(3)� [with Fe(2)].

The FeO2C3 chelate rings show some deviations from

planarity. This can be quantified by the angle between the FeO2

plane and the O2C3 plane in the chelate ring. These ‘folding

angles’ are relatively small for complex A [range 4.5(4)–10.7(4)�],while within complex B one ring is flat [angle of 0.1(3)�] and two

(symmetry equivalent) rings are quite folded [angle of 18.5(4)�].This is the major structural difference between A and B. The

planes of all the pyridyl groups show large rotations with respect

to the planes of their chelate rings [range 1.7(5)–49.7(7)�].The metalloligand is an octahedrally shaped building block

whose dimensions can be determined by the distances of the N

atoms of the pyridyl donor groups, i.e. on average ca. 9.73(2) �A

(A) and 9.81(2) �A (B) for the edges and ca. 13.78(3) �A (A) and

13.75(2) �A (B) for the diagonals.

An intriguing feature of this structure is the packing of the

discrete complexes that leaves large free voids corresponding to

22.6% (0.19 cm3 g�1) of the cell volume. A crystallographic cell

contains 12 complexes, 8 of type A (4DA + 4LA) and 4 of type B

(2DB + 2LB).

Complexes A form 2D layers that stack along a alternating

with 1D chains running in the c direction that contain only

complexes B (as illustrated in Fig. 2). The voids are located in the

parallel channels running along c.



Table 2 Crystallographic data

1a 2a 2b 2c 3a 4 5a

Formula C39H27FeN6O6

Fe(bppd)3

C55H59AgBF4

FeN6O10 [Fe(bppd)3Ag]BF4$4THF

C55H59AgClFeN6O14

[Fe(bppd)3Ag]ClO4$4THF

C55H59AgF6FeN6O10P [Fe(bppd)3Ag]PF6$4THF

C80H54Ag2F6

Fe2N12O18S2[Fe(bppd)3Ag](SO3CF3)

C78H54Ag3Fe2N15O21

[Fe2(bppd)6Ag3](NO3)3

C152H116Ag5Fe3N18O33S5[Fe3(bppd)9Ag5](tosylate)5

M 731.52 1214.61 1227.25 1272.77 1976.94 1972.67 3589.83System Orthorhombic Monoclinic Monoclinic Monoclinic Monoclinic Monoclinic TrigonalSpace group Pbcn C2/c C2/c C2/c Cc C2/c P�3c1a/�A 35.923(6) 13.246(14) 13.402(2) 13.359(3) 20.806(3) 20.341(3) 27.6841(11)b/�A 20.557(3) 22.90(2) 23.473(4) 23.669(5) 17.767(3) 17.552(3) 27.6841(11)c/�A 16.968(3) 17.291(18) 17.618(3) 17.737(4) 25.939(4) 26.677(4) 17.4801(14)a/� 90 90 90 90 90 90 90b/� 90 96.236(18) 96.560(2) 97.697(2) 98.751(2) 93.888(2) 90g/� 90 90 90 90 90 90 120U/�A3 12 530(4) 5214(9) 5506.1(16) 5558(2) 9477(3) 9502(3) 11 602.1(11)Z 12 4 4 4 4 4 2Temperature/K

RT 150 150 150 150 150 120

Density/gcm�3

1.163 1.558 1.480 1.521 1.386 1.379 1.028

Reflscollected

95 789 24 643 34 027 42 180 48 711 45 990 115 880

Indep. refls,R(int)

6573, 0.113 5618, 0.238 7114, 0.056 6609, 0.056 19 102, 0.078 8737, 0.081 7950, 0.107

Refls. Obs.[Fo > 4s(Fo)]

5039 2298 5200 5587 10 413 5271 3903

Data/Restr./Param.

5039/0/704 5618/21/288 7114/0/347 6609/21/364 19 102/3209/505 8737/219/532 7950/189/80

R1 [Fo > 4s(Fo)]

0.0989 0.1194 0.0464 0.0635 0.0996 0.0886 0.1667

wR2 (alldata)

0.2650 0.3169 0.1037 0.1625 0.3047 0.2611 0.4279

Fig. 1 The two adjacent independent tris-chelate complexes in

compound 1a0 [complex A, containing Fe(1), and complex B, containing

Fe(2)] that show opposite conformation (L and D). Complex B is located

on a 2-fold crystallographic axis. # Symmetry code: 2 � x, y, 1/2 � z.

Fig. 2 View of the packing down c in 1a0 (top) showing the stacking

(along a) of layers of complexesA (red) alternating with coplanar parallel

chains of complexes B (blue). The two types of sheets are illustrated

below, with different shadings that evidence the opposite conformations

(L and D) of the complexes.

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By reacting Hbppd and AlCl3 under the same conditions used

to obtain 1a, it was also possible to obtain the aluminium

derivative [Al(bppd)3] (1b). Compound 1b was isolated in good

yields as white microcrystalline powder and characterized by IR,1H NMR spectroscopy and XRPD. The X-ray powder diffrac-

tion patterns of 1a and 1b are comparable with one another but

different from the pattern calculated from the structure of 1a0

(see Fig. S1 and S2†).

This journal is ª The Royal Society of Chemistry 2011 CrystEngComm


Fig. 3 The geometry of the metalloligand (as observed in 2c) in the

polymeric frameworks of family 2 showing the four bonded ‘tetrahedral’

silver ions.

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The heterometallic coordination networks

Complex 1 is a suitable neutral metalloligand exhibiting six exo-

oriented donor pyridyl groups that can, in principle, work as a 6-

connected node in the building of heterometallic metal–organic

frameworks. Paralleling our recent work based on similar tris-

chelate metalloligands, [MIIIL3] [M ¼ Fe3+ and Co3+] and

[MIIL3]� [M ¼ Mn2+, Co2+, Zn2+, Cd2+] with HL ¼ 1,3-bis(4-

cyano-phenyl)-1,3-propanedione,8 we have reacted 1 with many

AgX salts. While the above [MIIIL3] and [MIIL3]� species affor-

ded in all cases the same type of 3D structure (6-fold inter-

penetrated pcu topology) that crystallizes in the same space

group with similar cell parameters,8 in spite of the different metal

ions, ionic charges and X� silver counter-anions, in the present

work we observe that with [Fe(bppd)3] (1) the outcoming MOFs

are varied and strongly dependent on the type of AgX salt

employed. We have obtained four different types of hetero-

metallic polymeric frameworks, i.e. a family of five isomorphous

2D single-sheet species (compounds 2a–e) when X� are pseudo-

spherical anions (tetrahedral or octahedral) of poor coordinating

ability, a 2D double-layered species (compound 3a) with silver

triflate, a 3D 2-fold interpenetrated complex network

(compound 4) with silver nitrate and a single 3D nanoporous

network (compound 5a) with silver tosylate (see Table 1). This

structural sequence illustrates also a progressive increase of the

pyridyl groups of the metalloligands that act as donors. Indeed,

though the building blocks are in principle able to work as six

donors, we observe here cases in which a lower donicity is present

(four or five donor groups employed) in all species but in

compound 5. The metalloligands contained as building blocks in

the heterometallic coordination networks maintain essentially

the same structure as in the free species.

Fig. 4 Side view of a single undulated 2D layer (down c) of compound

2c, showing the dangling pyridyl groups.

The family [Fe(bppd)3Ag](X)$4THF [X ¼ BF4�, ClO4

�, PF6�,

AsF6�, SbF6

�(2a–e)]

The reactions of 1 in THF with AgX salts (X� ¼ BF4�, ClO4

�,

PF6�, AsF6

�, SbF6�) in acetonitrile produce the family 2a–e.

Single crystals were obtained for all these species, showing that

they are isomorphous, but complete X-ray analyses were carried

out only for 2a–c, while the other two species gave crystals of

poorer quality and they were simply characterized by their cells,

exhibiting very similar parameters by single-crystal X-ray

diffraction. The general formulation is [Fe(bppd)3Ag](X)$4THF;

the structure with X� ¼ PF6� (2c) is described here, as repre-

sentative of the whole family.

The crystal structure of these species consists of 2D undulated

layers of 44-sql7a topology, showing the alternation of metal-

loligands and silver ions as 4-connected nodes. All the metal-

loligands are located in a special position on 2-fold axes and use

the two pyridyl groups of one bppd ligand and one pyridyl group

for each of the other two ligands to bind to silver metals (see

Fig. 3). Two cisoid pyridyl groups remain dangling so that the

node geometry can be described as of the saw-horse type.

The silver nodes, also lying on 2-fold axes, are distorted

tetrahedral, being bound to four N-pyridylic atoms with Ag–N

bond lengths of 2.284(4) and 2.332(4) �A and bond angles in

the range 98.5(2)–126.3(2)�. These two types of nodes produce

the undulated 2D layers, illustrated in Fig. 4. In these layers the

CrystEngComm

4-gon windows are 28-membered rings. These large rings can

be idealized to rhombuses with Fe/Ag edges of 9.110(2) and

9.270(2) �A. There are two kinds of rhombuses [Fe/Fe diago-

nals: 14.545(3) vs. 13.410(3) and Ag/Ag diagonals: 11.238(3) vs.

12.571(3)] that are alternately disposed, as a chessboard, with the

anions located in the more distorted windows (see Fig. 5).

Within each layer the metalloligands in the ‘upper’ rows

(crests) are all homochiral and of opposite chirality with respect

to those in the ‘lower’ rows (valleys).

The layers have a certain thickness (18.67 �A, from the top and

the bottom planes of the N atoms of the uncoordinated pyridyl

groups) and stack with an ABAB sequence down b (see Fig. 6)

with great interdigitation (overlap thickness of 4.83 �A).

The anions occupy intralayer spaces i.e. are placed at the

centers of alternate rhombic cavities (positions corresponding to

inversion centers). Four pyridyl groups are present in the edges

of the rhombuses, two (opposite) with their rings in the plane of

the window and two (opposite) with their rings almost perpen-

dicular (see Fig. 7). These cavities are particularly suited for the

encapsulation of octahedral anions such as PF6�, AsF6

� and

SbF6� (as well as disordered tetrahedral ones such as BF4

� and

ClO4�, with a sort of pseudo-octahedral shape) because of

significant s–anion (i.e. H-bonds) and p–anion interactions. Ab

initio theoretical calculations have recently shown that the anion-

binding properties of pyridine and pyrazine are dramatically

enhanced by their coordination to silver ions.18 The presence of

the coordinated metal increments both the p and the s anion-

binding ability. Detailed values of these interactions for the PF6�

and disordered ClO4� species are reported in the ESI†. The

presence of the anions in all 2a–e compounds was confirmed by

IR spectroscopy.

The THF molecules are placed in the interlayer spaces, near to

the more regular windows. The percentage of free void calculated



Fig. 5 Top views (down b) of the 2D layer of compound 2c: (top)

molecular drawing illustrating the presence of two types of windows

alternately disposed, as in a chessboard, and (bottom) a schematic

drawing with rhombuses having two kinds of vertexes (Fe and Ag, evi-

denced by different colors). The disposition of the anions (blue) and the

guest THF molecules (green) is also shown.

Fig. 7 View of a rhombic cavity containing PF6� in a layer of 2c. The

interactions of the pyridyl groups on the walls with the anions are dis-

cussed in the text.

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with the program PLATON after the removal of clathrate THF

molecules is 39.7% of the cell volume for 2c.

Thermal gravimetric analyses, performed on compounds 2a–d,

show that almost all the THF molecules are lost at

room temperature. The remainder (2–5%) is lost in the ranges

Fig. 6 Stacking of the layers in 2c.


20–100 �C for 2a,b (tetrahedral anions) and 20–170 �C for 2c,

d (octahedral anions). The networks decomposition starts at

different temperatures depending on the polymers (range

200–230 �C).

The double-layered [Fe(bppd)3Ag](CF3SO3) (3a)

The structure of [Fe(bppd)3Ag](CF3SO3) (3a), which exhibits the

same framework composition of the previous family 2, shows

a completely different type of [Fe(bppd)3Ag]+ 2D polymeric

frame, probably due to the variation in shape and chemical

behaviour of the anion that consists of a double layer, comprised

of two superimposed honeycomb-like sheets of 63-hcb7a topology.

The metalloligands again employ only four out of the six pyridyl

donor groups for networking (see Fig. 8). The three bppd

ligands, however, play different roles, i.e. in detail: the first ligand

uses both its pyridyl groups to bind two Ag atoms in one layer,

the second ligand uses only one pyridyl group to bind the third

Ag atom in the same layer, with the other pyridyl group dangling

outwards in the direction normal to the layer, while the third

ligand works as a bridge that joins the two layers, with one

pyridyl group that binds an Ag atom of the second layer and with

the remaining pyridyl group that is dangling in the plane of the

first layer.

There are two independent metalloligands [containing Fe(1)

and Fe(2), respectively] and two independent silver atoms. The

first metalloligand exhibits Fe(1)–O bond distances in the range

1.880(11)–2.029(8) �A and bite angles O–Fe(1)–O in the range

85.5(3)–86.6(4)�. All the three metallocycles are markedly

distorted from planarity, with O2C3/FeO2 angles in the range

Fig. 8 The geometry of the metalloligand in 3a with only four of the six

pyridyl groups bound to ‘tetrahedral’ Ag ions.

CrystEngComm


Fig. 10 Side view (top, evidencing the upper and lower dangling pyridyl

groups) and front view (bottom) of a homochiral double layer in 3. The

location of the triflate anions inside the intra-layer cages is shown with

different styles.

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18.9(5)–24.3(5)�. The pyridine rings are significantly rotated with

respect to the plane of the three central carbon atoms, with values

in the large range 12.1(4)–38.7(5)�. Within the other metal-

loligand the Fe(2)–O bond lengths span the interval 1.955(8)–

2.087(9) �A and the bite angles O–Fe(2)–O span the interval

87.3(3)–90.6(3)�. The three metallocycles are even more

deviating from planarity, with dihedral angles in the range

17.5(3)–27.4(8)�. Again the pyridine rings are strongly rotated

with respect to the central carbon atoms plane, with the value in

the large range 9.5(5)–37.1(8)�.The distorted tetrahedral silver atoms exhibit the following

bond parameters: Ag(1)–N 2.286(6)–2.313(8) �A and N–Ag(1)–N

97.4(3)–124.9(3)�, Ag(2)–N 2.296(6)–2.363(8) �A and N–Ag(2)–N

87.6(3)–125.9(3)�. Though the structural characterization has

been performed at 150 K, one coordinated pyridine ring is

disordered with two positions, with an occupancy of 63% and

37%.

The polymeric frame is a thick double layer (distance between

the planes containing the metalloligands in the two layers of

10.35 �A), formed by two superimposed 63-hcb7a sheets. Within

each sheet the 6-gons are comprised of alternating three metal-

loligands and three silver atoms. The silver nodes are 4-con-

nected (bound to three pyridyl groups of the same layer and to

one group from the other layer). A schematic view of the double

layer is shown in Fig. 9. The two sheets are staggered in such

a way that the silver atoms of the upper one correspond to the

iron metalloligands of the lower one (and vice versa). The

topology is that of an uninodal 2D network of point symbol

43.63; a previous example of double layer with this topology is

[RuCl2(pyz)4Ag](SO3CF3).3h The network edge dimensions are

Fe/Ag 9.049(4), 9.074(2), 9.129(2) �A and 9.061(2), 9.123(2),

9.139(3) �A (intralayer) and Fe/Ag 9.218(4) and 9.123(2) �A

(interlayer) (many details are reported in the ESI†).

Two views of the framework (side and top) are illustrated in

Fig. 10. As can be observed, there are some notable structural

features: (i) dangling pyridyl groups protrude outside the double

layer on both sides, which play an important role in the stacking

of these 2D motifs (see below); (ii) the framework contains cages

of idealized hexagonal prismatic shape that are occupied by the

triflate anions; (iii) remarkably all the metalloligands of an

individual double layer are homochiral (D or L), while the

adjacent double layers (upper and lower) show opposite chirality.

The double layers are parallel to the ab crystallographic plane

and stack in the normal direction (c*) with the lateral shift, as

shown in Fig. 11.

Fig. 9 Schematic view of the double layer in 3. Different colors are

employed for the iron and silver centers.

CrystEngComm

The dangling pyridyl groups on both sides of each double layer

are threaded into the 6-gon meshes of the two adjacent (upper

and lower) double layers, resulting in an extended polythreaded

array. The polythreading is favoured by p–p interactions that

involve the dangling pyridyl rings of adjacent double layers

(centroid–centroid distance of 3.690 �A).

The theoretical free space of this polymer is about 21.1% of the

cell volume.

The XRPD pattern of the bulk product shows a limited crys-

tallinity, but confirms that the structure is retained by compar-

ison with the calculated pattern. The presence of triflate anions

was confirmed by IR spectroscopy.

Fig. 11 Stacking of the double layers in 3, showing that the dangling

pyridyl groups are threaded into the adjacent upper and lower layers.



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The TGA of 3a showed a first weight loss of 2.3% in the range

20–185 �C, due to desolvation, and a second weight loss of 57.5%

starting at ca. 200 �C due to network decomposition.

Polycrystalline samples of the aluminium derivative

[Al(bppd)3Ag](CF3SO3) (3b) were obtained after reacting the

metalloligand 1b with silver triflate under experimental condi-

tions similar to those used to synthesize 3a. The nature of 3b was

assessed comparing its XRPD patterns with that of 3a.

The 3D interpenetrated species [Fe2(bppd)6Ag3](NO3)3 (4)

When silver nitrate and silver tosylate are used the anions

interact with the silver atoms and this results in the formation of

3D polymers, namely [Fe2(bppd)6Ag3](NO3)3 (4) and

[Fe3(bppd)9Ag5](tosylate)5 (5a).

The network of [Fe2(bppd)6Ag3](NO3)3 is strictly related to the

above described 2D structure of compound 3a [Fe(bppd)3Ag]

(CF3SO3). In this 3D network the same double layer of the 2D

structure, with similar bond parameters, is connected to two

adjacent (upper and lower) layers of the same type via additional

2-connected silver atoms. These silver atoms (see a schematic

view in Fig. 12) are coordinated by the dangling pyridyl groups

disposed above and below each double layer. In this way the

metalloligand becomes a 5-connected node and generates two

interpenetrating binodal 4,5-connected 3D networks. The Fe/Ag/Fe edges connecting the double layers are 17.637(3) �A long.

The point symbol of the single net is (43.63)(43.66.8) and the

system is 2-fold interpenetrated of Class IIa (the two nets are

related by an inversion centre), according to TOPOS that

describes it as a derived binodal net with the name fsx-4,5-R�3m.19

The silver atoms that work as spacers [Ag–N 2.114(13),

2.075(13) �A, N–Ag–N 163.3(5)�] lie close to inversion centres

(being therefore statistically disordered on two adjacent posi-

tions); they bear in addition a terminal weakly bonded nitrate

[Ag–O(NO3) 2.631(13) �A] and are inserted inside the cages of the

double layers (see above) belonging to the second interpenetrated

network. In other words, starting from the structure of

compound 3a, these silver atoms find their location approxi-

mately in the midpoint between each pair of pyridyl groups

Fig. 12 Schematic view of the two-fold interpenetrated 4,5-connected

network in 4; its origin from the double-layered structure of compound

3a via silver bridges is evidenced. The two 3D interpenetrating nets have

opposite chirality.


threading the double layers by opposite directions [the (py)N/N

(py) nonbonding contact passes from 3.43(2) �A in 3a to 4.14(2) �A

in 4] (see Fig. 13).

The chirality pattern of the metalloligands observed in 3a

(alternation of ‘all D’ double layers with ‘all L’ double layers) is

maintained in 4: thus the additional Ag spacers form two 3D nets

of opposite chirality (a crystalline racemate).

It is worth noting that the previously reported reactions of the

strictly related metalloligands [M(bppd)3] (M ¼ Al3+ or Ga3+)

with AgNO3 afford a quite different and more usual coordina-

tion polymer, i.e. a 3-fold interpenetrated pcu network.10

TGA of compound 4 showed a weight loss of about 2% in the

20–130 �C range due to desolvation and a second weight loss of

about 62.6%, starting at 150 �C, due to network decomposition.

The structural correlation observed between compounds 3a

and 4 has prompted us to attempt to transform the former one

into the second by reacting powder samples of 3a with a solution

of silver nitrate. The transformation has been monitored by

XRPD and IR spectroscopy (see Fig. S7 and S8†). The results

show that the final product presents a powder diffraction pattern

very similar to that of 4 but the IR spectrum reveals the presence

of both anions (triflate and nitrate), i.e. the triflate anions have

not been completely displaced and the compound is a mixed salt,

isomorphous with 4.

The 3D nanoporous [Fe3(bppd)9Ag5](tosylate)5 (5a)

The reaction of 1 with silver tosylate produces a complex 3D

nanoporous network, [Fe3(bppd)9Ag5](tosylate)5 (5a), exhibiting

6-connected metalloligands and 3- and 4-connected silver ions. It

is worth noting that it is the unique network within these heter-

ometallic Fe/Ag species in which 1 uses all the six pyridyl donor

groups.

This metalloligand was just intended as an octahedral 6-con-

nected building block for the engineering of networks, and such

a behaviour has been previously observed with strictly similar

metalloligands8,10 that, by reactions with silver salts, generate

frameworks showing the 6-c pcu7a topology. At difference, the

Fig. 13 A single network in 4 (left). The silver bridges are statistically

disordered, as shown in detail in the right drawing, about inversion

centers.

CrystEngComm


Fig. 15 View of the nanoporous network in compound 5a.

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single 3D network of 5a exhibits a novel trinodal topology, with

3-connected (3-c, Ag), 4-connected (4-c, Ag) and 6-connected

(6-c, Fe) nodes in the ratio 2 : 3 : 3, i.e.with the [(3-c)2(4-c)3(6-c)3]

stoichiometry and point symbol (63)2(44.62)3(4

4.65.86)3.

Within the metalloligand the Fe–O bond distances are in the

range 1.931(7)–1.993(8) �A and the O–Fe–O bite angles are in the

range 87.6(3)–88.5(4)�, similar to the values in 1a0. One metal-

locycle is very close to planarity (dihedral angle of 0.4(5)�) whilethe other two equivalent show a large deviation (dihedral angle

of 28.1(7)�). Also in this case the pyridine rings are strongly

rotated with respect to the plane of the three central carbon

atoms (range 3.8(6)–35.2(6)�).An interesting rationalization of this novel network is the

following one: large 1D parallel metal–organic nanotubular

motifs of hexagonal section can be envisaged, all running in the c

axis direction, with square-meshed walls that are laterally inter-

connected by additional Ag triple-bridging atoms to generate the

whole 3D array.

A single nanotube is illustrated in Fig. 14; its stoichiometry is

[Fe(bppd)3Ag]+, like that of the previously described 2D species 2

and 3a. It can be conceptually considered as a rolled version of

a single 44-sql7a layer of compounds 2 (obviously in this case with

the dangling pyridyl groups all oriented on the same side, i.e.

outwards the tube), with the walls of the tube formed by the same

type of square meshes as in 2. Independent metal–organic

nanotubes, held together by alkaline cations, with a similar

topology have been recently described,20 based on Cd2+ ions and

the bent ligand 4-amino-3-[(pyridin-4-ylmethylene)amino]

benzoate. From a theoretical point of view, the curling-up or

rolling-up mechanism of topological transformation from 2D

sheets to 1D tubes is illustrated by the structural comparison of

a single 2D layer of 2 with a nanotube of 5a. It is worth noting

that like the rolling-up of graphite to single walled carbon

nanotubes can be ideally carried out in different ways, also

within metal–organic nanotubes, the parent 44-sql7a layers can be

rolled in such a way to dispose along the tube axis either the

4-gon diagonals, as in the Cd species previously cited,20 or the

4-gon edges as in 5a.

Another interesting structural similarity can be envisaged: the

nanotubes originate from the superposition of hexagonal rings

similar to those of the honeycomb-like layers of 3a, constituted

Fig. 14 Molecular (top) and schematic (bottom) front and side views of

a nanotube in 5a. The orange spheres represent Fe atoms and the pink

spheres represent Ag atoms.

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by alternating three silver atoms and three metalloligands. The

superposition of the rings occurs in a staggered fashion, like in

3a. The three metalloligands in a ring are homochiral while those

of the two adjacent rings (upper and lower) show opposite

conformation. A nanotube is therefore a DLDL. sequence of

rings.

These tubular motifs are connected among them via the two

remaining pyridyl groups of each metalloligand that are coor-

dinated to 3-connected silver atoms. These 3-connected silver

atoms have the function to link and space out the tubes three by

three (see Fig. 15 and 16). These Ag nodes lie on 3-fold axes and

exhibit a pyramidal geometry, being bound to three pyridyl

nitrogen atoms [Ag–N 2.27(1) �A and N–Ag–N 113.4(5)�] andweakly interacting with a (disordered) tosylate anion [Ag–O

2.275(13) �A]. Though the X-ray data collection has been per-

formed at 120 K, the anion is strongly disordered on three

positions, with an occupancy of 33%.

The network presents high theoretical porosity of about 50%

of the unit cell volume; the voids are mainly distributed in the

large hexagonal channels (i.e. in the single walled metal–organic

nanotubes, Fig. 16).

The XRPD pattern of the bulk product 5a shows a different

crystalline structure when compared with the pattern calculated

from single crystal. On the other hand, it is comparable with the

powder pattern of ground single crystals. A possible explanation

is that the structure of 5a, probably due to the loss of guest

solvents, rearranges to a different uncharacterised species. The

presence of the anions was confirmed by IR spectroscopy.

Fig. 16 Schematic view of the network in 5 evidencing the nanotubes (in

red).



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TGA of compound 5a showed a weight loss of about 4.9% in

the 20–120 �C range due to desolvation and a second weight loss,

starting at 250 �C, of about 47.6% corresponding to network

decomposition.

The aluminium derivative [Al3(bppd)9Ag5](tosylate)5 (5b) was

also obtained as a polycrystalline material. The nature of 5b was

confirmed by comparison of its XRPD powder pattern with that

obtained by grinding crystals of 5a.

Conclusions

In this paper we have investigated the use of the novel metal-

loligand [Fe(bppd)3] (1a) as well as the aluminium analogue for

the construction of heterometallic networks by reactions with

silver salts. This well-established synthetic strategy, involving the

use of rigid building blocks with exo-donor groups, can some-

times result in structural motifs different from the target struc-

ture because not all the potential donor groups are used in the

networking process. The results reported here, at difference from

what was observed in other studies involving similar tris-chelate

octahedral complexes with six exo-oriented donor groups,8,10

show that 1a can employ four, five or six pyridyl donors to give

a variety of heterometallic networks depending on the nature of

the silver counter anion. We have obtained a family of 2D 44-sql

networks with undulated single layers of rhombic meshes that

contain anions that are pseudo-spherical [e.g. BF4�, ClO4

�, PF6�,

AsF6�, SbF6

�(2a–e)]. In these species the metalloligands use only

four of the donor pyridyl groups. The same occurs in compound

3a that contains triflate anions. This polymer has a network

stoichiometry like that of the family 2 but with a completely

different and unusual structure, consisting of double honey-

comb-like layers (uninodal 2D net 43.63) with dangling pyridyl

groups on both sides that give polythreading with the adjacent

(upper and lower) identical motifs. More intriguing are the

structures of the 3D species 4 (with AgNO3) and 5a (with Ag

tosylate). The structure of 4 is strictly correlated with that of 3a:

the double layers are connected by Ag diagonal bridges into

a 2-fold interpenetrated 3D binodal 4,5-connected network. The

most interesting feature consists of the fact that the framework of

4 can be recovered by transforming 3a, i.e. by reacting powder

samples of 3a with AgNO3. Finally, the structure of 5a, obtained

by reaction of 1awith silver tosylate, is very interesting both from

a structural and a functional point of view: it contains 1D metal–

organic nanotubes with a large cross-section joined by 3-con-

nected Ag atoms into a nanoporous 3D array with large voids

(ca. 50% of the cell volume). Thus the anions show, in this family,

a fundamental role in driving the outcoming heterometallic

network.

Acknowledgements

This work was supported by MIUR within the project PRIN

2008 CRYSFORMS: ‘‘Design, properties and preparation of

molecular crystals and co-crystals’’.

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CrystEngComm Dynamic Article LinksC Cite this: DOI: … · Lucia Carlucci,* Gianfranco Ciani, Davide M. Proserpio and Marco Visconti Received 4th May 2011, Accepted 6th July 2011