Co (II), Ni(II) and Cu(II) complexes with a new pendant armed macrocyclic ligand showing several π,π-interactions

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Inorganica Chimica Acta 358 (2005) 2618–2628

Co (II), Ni(II) and Cu(II) complexes with a new pendantarmed macrocyclic ligand showing several p,p-interactions

Laura Valencia *, Rufina Bastida *, Ma del Carmen Fernandez-Fernandez,Alejandro Macıas, Manuel Vicente

University of Santiago de Compostela, Departamento de Quımica Inorganica, Avenida de las Ciencias s/n, 15782 Santiago de Compostela, Spain

Received 8 September 2004; accepted 1 March 2005

Available online 6 April 2005

Abstract

A new ligand, L, bearing four cyanoethyl pendant groups has been synthesized by reaction of the precursor ligand L1 with acry-

lonitrile. The X-ray crystal structure of ligand L reveals the presence of a nanotubular structure in the solid state connected by inter-

molecular p,p-stacking interactions between adjacent pyridine rings. The coordination capability towards transition metal ions

[Co(II), Ni(II) and Cu(II)] has been investigated starting from the hydrated nitrate and perchlorate salts of the metals. The new

ligand L and the metal complexes obtained were characterized by elemental analysis, FAB MS, conductivity measurements,

magnetic studies, IR and UV–vis spectroscopy. Furthermore, the crystal structure of ligand L and of the complexes [CoL][Co

(NO3)4] Æ CH3CN (1), [NiL](NO3)2 (3), [NiL](ClO4)2 Æ CH3CN Æ 3H2O (4), [CuL][Cu(NO3)3(H2O)2](NO3) Æ H2O (5) and [CuL]

(ClO4)2 Æ 2CH3CN (6) were determined. The nitrate ions in the complexes are located near the pyridine rings and p,p-stacking inter-

actions between pyridine rings, nitrate ions and nitrile groups have been found.

� 2005 Elsevier B.V. All rights reserved.

Keywords: Macrocycle; Transition metal ions; p,p-stacking; Metal complexes; Crystal structures

1. Introduction

In recent decades, azamacrocyclic ligands have been

the subject of many investigations as they tend to exhibit

high thermodynamic and kinetic stabilities and also

show interesting coordination properties – they are

capable of forming mononuclear and dinuclear com-

plexes [1–3]. Oxaaza- and azamacrocycles containing

pyridine rings have been the subject of numerous inves-tigations by our research group [4–7]. It has been shown

that p,p-interactions between aromatic rings play an

important role in how the complexes or coordination

polymers are packed in the crystal lattice, and a wide

0020-1693/$ - see front matter � 2005 Elsevier B.V. All rights reserved.

doi:10.1016/j.ica.2005.03.010

* Corresponding author. Tel.: +34 981 528 073; fax: +34 981 597 525.

E-mail addresses: [email protected] (L. Valencia), [email protected]

(R. Bastida).

variety of p,p-interactions have been reported betweenaromatic groups. In previous papers, we reported the

coordination capability of different azamacrocycles

bearing pendant arm groups derived from the ligand

L1 (see Scheme 1) [8,9]. The cavity of this 18-membered

precursor does not seem appropriate for encapsulating

two metal ions; nevertheless, the presence of additional

donor atoms on the pendant groups usually led to differ-

ent and unexpected stoichiometries and coordinationgeometries in the complexes [10]. The linear nature of

the nitrile groups does not allow them to participate in

intramolecular coordination but they can interact with

additional metal ions. As part of our ongoing program,

a new macrocyclic ligand L, which contains two pyridine

rings in the ligand skeleton and bears four cyanoethyl

pendant groups, has been synthesized. In the solid state,

L presents a nanotubular structure arranged by p,p-stacking interactions between the pyridine groups. This

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Scheme 1.

L. Valencia et al. / Inorganica Chimica Acta 358 (2005) 2618–2628 2619

situation is similar to that previously described for L2.

The complexation capacity of the ligand L toward a

range of first row transition metals has been studied.

The crystal structures of [CoL][Co(NO3)4] Æ CH3CN(1), [NiL](NO3)2 (3), [NiL](ClO4)2 Æ CH3CN Æ 3H2O (4),

[CuL][Cu(NO3)3(H2O)2](NO3) Æ H2O (5) and [CuL]

(ClO4)2 Æ 2CH3CN (6) were determined. The X-ray

structure of the nitrate complexes reveals p,p-stackinginteractions between pyridine rings, nitrate ions and ni-

trile groups.

2. Experimental

2.1. Measurements

Elemental analyses were performed on a Carlo-Erba

EA microanalyser. Infra-red spectra were recorded as

KBr discs on a Bruker IFS-66V spectrometer. L-SIMS

mass spectra were recorded using a Micromass Autospec

spectrometer with 3-nitrobenzyl alcohol as the matrix.

Conductivity measurements were carried out in

10�3 mol dm�3 DMF solutions at 20 �C using a WTW

LF3 conductivimeter. The 1H NMR spectrum of L

was recorded on a Bruker 500 MHz spectrometer and

CD3CN was used as the solvent. Solid state electronic

spectra were recorded on a Hitachi 4-3200 spectropho-

tometer using MgCO3 as a reference. Magnetic studieswere performed at r.t. on a vibration sample magnetom-

eter (VSM) Digital Measurement System 1660 with a

magnetic field of 5000 G.

2.2. Chemicals and starting materials

2,6-Pyridinedimethanol, ethylenediamine, acryloni-

trile and hydrated nitrate and perchlorate salts werecommercial products (from Alfa and Aldrich) and were

used without further purification. Solvents were of re-

agent grade and were purified by the usual methods.

Caution: Although problems were not encountered dur-

ing the course of this work, attention is drawn to the

potentially explosive nature of perchlorates.

2.3. Synthesis of the macrocycle L

Synthesis of the precursor ligand L1. The synthesis of

L1 was achieved following the literature method [11]. A

solution of ethylenediamine (0.67 ml, 10 mmol) was

added dropwise to a refluxing suspension of barium(II)

chloride dihydrate (1.22 g, 5 mmol) and 2,6-diformyl-

pyridine [12] (1.35 g, 10 mmol) in methanol (200 ml).

The mixture was refluxed for 4 h and the solution wasallowed to cool to room temperature. Sodium tetrahyd-

roborate (1.52 g, 40 mmol) was added slowly; after

30 min a second portion of NaBH4 (0.76 g, 20 mmol)

was added. The mixture was stirred for 1.5 h and con-

centrated to dryness under reduced pressure. The crude

solid was extracted with chloroform (3 · 100 ml) and a

brown oil was obtained. This oil was dissolved in meth-

anol and hydrobromic acid was added dropwise untilacidic pH. The tetrahydrobromide salt of the ligand L1

was isolated.

Synthesis of L. L1 (3 mmol, 2 g) was dissolved in

acrylonitrile (30 mL) and the solution refluxed for

24 h. The solution was filtered off and evaporated to

dryness. The residue was then extracted with water/chlo-

roform. The organic layer was dried over MgSO4 and

evaporated to yield an orange solid, which was recrystal-lized from acetonitrile to give the ligand L as a white

solid.

Anal. Calc. for C30H38N10 (MW: 538.70) C, 66.9; H,

7.1; N, 26.0. Found: C, 66.7; H, 7.0; N, 26.1%. Yield:

75%. IR (KBr, cm�1): 1594, 1457, [m (C@N)py and

m(C@C)], 2245 [m(C„N)]. (L-SIMS, m/z): [L1]+ 483. Col-

our: white.

2.4. Synthesis of the metal complexes – general procedure

The appropriate metal salt (0.37 mmol) was dissolved

in acetonitrile (10 mL) and added to a stirred solution of

Table 1

Crystal data and structure refinement for L, 1, 3, 4, 5 and 6

L [CoL][Co(NO3)4] ÆCH3CN (1)

[NiL](NO3)2 (3) [NiL](ClO4)2 ÆCH3CN Æ 3H2O (4)

[CuL][Cu(NO3)3(H2O)2] Æ(NO3) Æ H2O (5)

[CuL](ClO4)2 Æ2CH3CN (6)

Empirical formula C30H38N10 C32H41N15O12Co2 C30H38N12NiO6 C32H41N11O11Cl2Ni C30H38N14O15Cu2 C34H44N12O8Cl2Cu

Formula weight 538.70 945.66 721.43 885.37 961.82 883.25

Temperature (K) 298(2) 293(2) 293(2) 293(2) 293(2) 293(2)

Wavelength (A) 1.54184 0.71073 0.71073 0.71073 0.71073 0.71073

Crystal system monoclinic monoclinic monoclinic monoclinic triclinic monoclinic

Space group P21/c P21/n P21/n P21/n P�1 P21/n

Unit cell dimensions

a (A) 10.7475(8) 12.242(3) 10.7452(10) 11.154(2) 11.0370(9) 11.138(5)

b (A) 5.6114(9) 20.956(4) 15.3462(14) 25.914(6) 11.9928(10) 25.135(11)

c (A) 24.905(3) 15.515(3) 19.7356(18) 16.231(3) 15.9363(15) 16.148(7)

a (�) 90.964(7)

b (�) 92.293(7) 91.974(4) 92.415(2) 95.110(5) 93.125(7) 94.161(9)

c 96.950(7)

Volume (A3) 1500.8(3) 3978.0(14) 3251.5(5) 4673.2(17) 2090.2(3) 4509(3)

Z 2 4 4 4 2 4

Dcalc (mg/m3) 1.192 1.579 1.474 1.258 1.528 1.301

Absorption coefficient (mm�1) 0.593 0.915 0.660 0.590 1.099 0.661

F(000) 576 1952 1512 1840 988 1836

Crystal size (mm3) 0.28 · 0.20 · 0.08 0.65 · 0.61 · 0.51 0.36 · 0.18 · 0.05 0.46 · 0.28 · 0.27 0.31 · 0.22 · 0.13 0.40 · 0.40 · 0.35

h Range for data collection (�) 3.55–72.90 1.63–26.42 1.68–28.05 1.48–28.08 1.28–26.46 1.50–26.42

Index ranges �13 6 h 6 13,

�6 6 k 6 0,

�30 6 l 6 0

�15 6 h 6 15,

0 6 k 6 26,

0 6 l 6 19

�14 6 h 6 14,

�20 6 k 6 20,

�13 6 l 6 26

�14 6 h 6 14,

�27 6 k 6 34,

�21 6 l 6 17

�13 6 h 6 13,

�15 6 k 6 15,

0 6 l 6 19

�13 6 h 6 13,

0 6 k 6 31,

0 6 l 6 20

Reflections collected 3053 24489 17970 23947 25697 25036

Independent reflections [Rint] 2976 [0.0489] 8152 [0.0239] 7305 [0.0681] 10224 [0.1187] 8521 [0.0677] 9140 [0.0509]

Completeness to theta 100.0% (72.90�) 99.6% (26.42�) 92.6% (28.05�) 89.9% (28.08�) 99.2% (26.46�) 98.6% (26.42�)Absorption correction None SADABS SADABS SADABS SADABS SADABS

Maximum and minimum

transmission

0.9541 and 0.8515 0.6526 and 0.5878 0.9677 and 0.7969 0.8569 and 0.7730 0.8703 and 0.7268 0.8016 and 0.7779

Refinement method full-matrix least-

squares on F2

full-matrix least-

squares on F2

full-matrix least-

squares on F2

full-matrix least-

squares on F2

full-matrix least-

squares on F2

full-matrix least-

squares on F2

Data/restraints/parameters 2976/0/181 8152/0/551 7305/0/442 10224/0/500 8521/0/550 9140/6/517

Goodness-of-fit on F2 1.054 1.015 0.731 0.854 1.073 1.209

Final R indices [I > 2r(I)] R1 = 0.0719,

wR2 = 0.2188

R1 = 0.0481,

wR2 = 0.1306

R1 = 0.0462,

wR2 = 0.0644

R1 = 0.0884,

wR2 = 0.2132

R1 = 0.0692,

wR2 = 0.1914

R1 = 0.2051,

wR2 = 0.4910

R indices (all data) R1 = 0.1524,

wR2 = 0.2617

R1 = 0.0665,

wR2 = 0.1481

R1 = 0.1578,

wR2 = 0.0825

R1 = 0.2921,

wR2 = 0.2672

R1 = 0.1152,

wR2 = 0.2196

R1 = 0.2322,

wR2 = 0.5066

Extinction coefficient 0.0129(16)

Largest difference in peak

and hole (e A3)

0.397 and �0.235 1.765 and �0.850 0.277 and �0.239 0.646 and �0.465 0.976 and �0.783 3.586 and �1.596

2620

L.Valen

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al./Inorganica

Chim

icaActa

358(2005)2618–2628


the ligand L (0.135 g, 0.25 mmol) in acetonitrile

(20 mL). The solution was stirred for 2 h. The low solu-

bility of the nitrate complexes at room temperature in

this solvent led to the formation of crystalline precipi-

tates immediately after addition of the metal salts. The

resulting solids were isolated, dried under vacuum andrecrystallized from hot acetonitrile or water. The solu-

tions of the perchlorate complexes were concentrated

in a rotary evaporator until the volume was ca. 5–

6 mL. The resulting products were filtered off, dried

and recrystallized from acetonitrile or water.

2.5. [CoL][Co(NO3)4] Æ CH3CN (1)

Anal. Calc. for C32H41N15O12Co2 (MW: 945.6): C,

40.6; H, 4.4; N, 22.2. Found: C, 39.7; H, 4.6; N,

21.9%. Yield: 49%. IR (KBr, cm�1): 1614, 1579, 1473

[m(C@N)py and m(C@C)], 2426, 2252 [m(C„N)], 1449,

1383, 1300 ½mðNO3�Þ�. MS (L-SIMS, m/z): 597 [CoL]+,

659 [CoL(NO3)]+. KM/X�1 cm2 mol�1 (in DMF): 180

(2:1). Colour: violet.

2.6. [CoL](ClO4)2 Æ 4H2O (2)

Anal. Calc. for C30H46N10O12Cl2Co (MW: 868.6): C,

41.5; H, 5.3; N, 16.1. Found: C, 41.1; H, 5.9; N, 16.8%.

Yield: 47%. IR (KBr, cm�1): 1609, 1583, 1456 [m(C@N)pyand m(C@C)], 2252 [m(C„ N)], 1100, 627 ½mðClO4

�Þ�. MS

(L-SIMS, m/z): 597 [CoL]+, 697 [CoL(ClO4)]+.

KM/X�1 cm2 mol�1 (in DMF): 153 (2:1). Colour: blue.

2.7. [NiL](NO3)2 (3)

Anal. calc. for C30H38N12O6Ni (MW: 721.4): C, 49.9;

H, 5.3; N, 23.3. Found: C, 49.5; H, 5.3; N, 23.1%. Yield:

65%. IR (KBr, cm�1): 1609, 1581, 1476 [m(C@N)py and

m(C@C)], 2426, 2250 [m(C„N)], 1454, 1384, 1343

½mðNO3�Þ�. MS (L-SIMS, m/z): 596 [NiL]+, 658 [NiL

(NO3)]+. KM/X�1 cm2 mol�1 (in DMF): 133 (2:1). Col-

our: blue.

2.8. [NiL](ClO4)2 Æ CH3CN Æ 3H2O (4)

Anal. Calc. for C32H47N11O11Cl2Ni (MW: 891.4): C,

43.1; H, 5.3; N, 17.3. Found: C, 43.1; H, 5.0; N, 17.2%.

Yield: 55%. IR (KBr, cm�1): 1610, 1582, 1475 [m(C@N)pyand m(C@C)], 2253 [m(C„N)], 1089, 625 ½mðClO4

�Þ�. MS

(L-SIMS, mz): 596 [NiL]+, 695 [NiL(ClO4)]+. KM/

X�1 cm2 mol�1 (in DMF): 161 (2:1). Colour: blue.

2.9. [CuL][Cu(NO3)3(H2O)2] Æ (NO3) Æ H2O (5)

Anal. Calc. for C30H44N14O15Cu2 (MW: 967.9): C,

37.2; H, 4.6; N, 20.3. Found: C, 37.6; H, 4.5; N,20.3%. Yield: 46%. IR (KBr, cm�1): 1616, 1579, 1474

[m(C@N)py and m(C@C)], 2426, 2251 [m(C„ N)], 1446,

1383, 1350 ½mðNO3�Þ�. MS (L-SIMS, m/z): 601 [CuL]+.

KM/X�1 cm2 mol�1 (in DMF): 172 (2:1). Colour: green.

2.10. [CuL](ClO4)2 Æ 2CH3CN (6)

Anal. Calc. for C34H44N11O8Cl2Cu (MW: 869.2): C,47.0; H, 5.1; N, 17.7. Found: C, 46.9; H, 5.0; N,

17.9%. Yield: 62%. IR (KBr, cm�1): 1617, 1579, 1475

[m(C@N)py and m(C@C)], 2250 [m(C„N)], 1120, 627

½mðClO4�Þ�. MS (L-SIMS, m/z): 601 [CuL]+. KM/

X�1 cm2 mol�1 (in DMF): 160 (2:1). Colour: green.

2.11. X-ray crystallographic study

Slow recrystallization from acetonitrile or water gave

crystals of [CoL][Co(NO3)4] Æ CH3CN (1), [NiL](NO3)2(3), [NiL](ClO4)2 Æ CH3CN Æ 3H2O (4), [CuL][Cu(NO3)3(H2O)2] Æ (NO3) Æ H2O (5) and [CuL](ClO4)2 Æ 2CH3CN

(6) suitable for X-ray diffraction. The details of the

X-ray crystal data, and the structure solution and refine-

ment for all complexes are given in Table 1. Measure-

ments were made on a Bruker SMART CCD 1000 areadiffractometer. All data were corrected for Lorentz and

polarization effects. Empirical absorption corrections

were also applied for all the crystal structures obtained

[13]. Complex scattering factors were taken from the pro-

gram package SHELXTL [14]. The structures were solved

by direct methods, which revealed the position of all

non-hydrogen atoms. All the structures were refined on

F2 by a full-matrix least-squares procedure using aniso-tropic displacement parameters for all non-hydrogen

atoms. The hydrogen atoms were located in their calcu-

lated positions and refined using a riding model. Molec-

ular graphics were generated using ORTEP-3 [15]. The

free nitrate and perchlorate ions present in 3, 4, 5 and

6 were refined with no disorder, giving bond distances

and angles typical for those ions.

3. Results and discussion

The macrocyclic ligand L1 was prepared by barium-

template condensation of ethylenediamine and 2,6-dif-

ormylpyridine followed by reduction with NaBH4 as

reported previously [11]. The tetracyanoethylated mac-

rocycle L was obtained by reaction of L1 with acryloni-trile under reflux for 24 h. The ligand L was isolated as

an air-stable white solid in 75% yield and was character-

ized by elemental analysis, FAB MS, IR and 1H NMR

spectroscopy. The infrared spectrum (KBr disc) of L

contains a strong band at 2245 cm�1 attributable to

m(C„N), a feature that supports the formation of the

tetracyanoethylated macrocycle. The other absorption

bands corresponding to m(C@N) and m(C@C) vibrationsfrom the pyridine groups appear in their expected posi-

tions at 1594 and 1457 cm�1, respectively.

2622 L. Valencia et al. / Inorganica Chimica Acta 358 (2005) 2618–2628

The FAB MS of L shows the parent peak at m/z 539,

further confirming the presence of the ligand. The 1H

NMR spectrum of L was recorded in deuterated aceto-

nitrile and confirms the integrity of the ligand and its

stability in solution. The spectrum shows that the four

quadrants of the macrocyclic ligand are chemicallyequivalent, as one would expect with this kind of system.

The pyridine hydrogens exhibit the expected triplet and

doublet splitting patterns and the chemical shifts are

also consistent with the proposed structure. Two singlets

appear in the aliphatic region of the spectrum and these

Fig. 1. (a) Crystal structure of the ligand L; (b) Packing of ligand L along the

along the a axis of the crystal.

correspond to Py–CH2–N and N–CH2–CH2–N at 3.58

and 2.53 ppm, respectively. The two triplets observed

at 2.46 and 2.84 ppm are attributable to the ethylenic

fragment of the pendants.

Recrystallization of L from acetonitrile yielded crys-

tals that were suitable for X-ray diffraction. The crystal-lographic summary is given in Table 1 and the molecular

structure is shown in Fig. 1(a). The crystal belongs to the

monoclinic space group P21/c. Bond lengths and angles

determined for the structure fall within the normal

ranges. The pyridine rings of the macrocyclic backbone

b axis in the crystal lattice to form nanotubes; (c) Chains of L molecules


are parallel and the four amine nitrogen atoms are in a

plane. As in L1, the structure shows a markedly stepped

conformation, with a dihedral angle of 81.48(0.10)�(77.30 for L1) between the plane containing the pyridyl

groups and the plane that contains the four aliphatic

nitrogen atoms. The X-ray structural analysis of Lshows the formation of nanotubes along the b axis of

the crystal (Fig. 1(b)) stabilized by the presence of inter-

molecular p,p-stacking interactions, a situation that also

occurs in L2.

Analysis of the short intermolecular ring–ring inter-

actions in L reveals that side-on p,p-interactions partic-ipate in the molecular recognition process. The ligand L

forms chains along the a axis (Fig. 1c) by intermolecularslipped p,p-stacking interactions between pyridine rings

of adjacent ligands. The distance dc–c has a value of

5.22 A. The planes containing the pyridine rings of

two adjacent molecules lie parallel (a = 0�) and the inter-

planar distance is 3.16 A. The pyridine units are slipped

to a reasonable extent, with a slipping angle (b) (definedby the vector c1–c2 and the normal to the planes con-

taining the pyridine rings) of 52.7�.As far as the molecular recognition processes and

building of crystals are concerned, an intramolecular

p,p-stacking interaction does not exist between the pyr-

idine rings. These rings also lie parallel but the interpla-

nar distance of 4.32 A, with a dc–c value of 5.68 A, is too

high for a p,p-interaction to be considered between them

[16].

The coordination ability of ligand L towards hydratednitrate and perchlorate salts of Co(II), Ni(II) and Cu(II)

was studied. The reaction of L with the metal salts in a

1.5:1 metal-to-ligand ratio in acetonitrile led to the for-

mation of compounds with a 1:1 metal-to-ligand ratio

of the type [ML](X)2 Æ xCH3CN Æ yH2O (X ¼ NO3� or

ClO4�) for all metal salts, except when Co(NO3)2 and

Cu(NO3)2 were used. The microanalysis data suggest a

2:1 metal-to-ligand stoichiometry for the latter com-plexes. The ring size of L is insufficient for the formation

of endomacrocyclic dinuclear metal complexes, but the

presence of the nitrile groups can give rise to unexpected

coordination modes. Nevertheless, the resolution of the

crystal structures of [CoL][Co(NO3)4] Æ CH3CN and

[CuL][Cu(NO3)3(H2O)2] Æ (NO3) Æ H2O reveals the pres-

ence of independent cationic and anionic complexes of

the type [ML]2+ and [M(NO3)n Æ (H2O)m]y� in both cases.

The results of the L-SIMS MS of the complexes pro-

vide important evidence to confirm the 1:1 stoichiometry

of the complexes as they feature peaks attributable in all

cases to the mononuclear species [MLX]+ or [ML]+.

Molar conductivity data were measured at room tem-

perature using DMF as solvent (10�3 M solutions of the

complexes) due to the low solubility of some nitrate

complexes in acetonitrile. The molar conductivity valuesobtained for all complexes lie in the range previously ob-

served for 2:1 electrolytes [17].

4. Structural studies of the complexes

Crystals suitable for X-ray diffraction were obtained

by recrystallization of the products from acetonitrile

for 1, 3 and 6 or water for 4 and 5. The crystallographic

summary is given in Table 1 and selected bond lengthsand angles are given in Table 2. The ORTEP diagrams

are shown in Figs. 2–4 together with the atom notation

scheme adopted.

In all cases, the dication [ML]2+ is present. Each me-

tal ion in [ML]2+ displays a distorted octahedral coordi-

nation environment with the equatorial plane defined by

the four amine nitrogen atoms from the macrocycle. The

axial positions are occupied by the pyridinic nitrogenatoms. The distances Npy–M are shorter than those to

the tertiary amine nitrogen atoms (Nam–M), as one

would expect with this kind of ligand bearing pyridyl

rings in the macrocyclic framework [18]. The angle

Npy–M–Npy is always the closest to 180�.The structure of the ligand in those [ML]2+ ions

shows a �twist-wrap� conformation, where the ligand

wraps round the metal ion by twisting of the pyridylbridgehead units relative to each other. The macrocycle

adopts a helical shape, with an average value for the

rotation angle between pyridine rings of 74� [minimum

value 73.07� for [NiL](ClO4)2 Æ CH3CN Æ 3H2O and

maximum value 74.92� for [NiL](NO3)2]. The angles

Npy–M–Npy show that the macrocycles are not folded.

In all cases, the N atoms of the nitrile groups are not

coordinated to the metal due to their linear nature.Crystals of [CoL][Co(NO3)4] Æ CH3CN (1) also con-

tain the [Co(NO3)4]2� anion and an interstitial acetoni-

trile molecule. [Co(NO3)4]2� (Fig. 4) consists of four

nitrate ions around the Co(II) ion in a distorted trigonal

bipyramidal environment (s = 0.36) [19]. Three nitrate

ions act as monodentate groups, whilst the fourth one

chelates the Co(II) ion and acts as a bidentate group.

[CuL][Cu(NO3)3(H2O)2](NO3).H2O (5) contains themonoanion [Cu(NO3)3(H2O)2]

� (Fig. 4) where the

Cu(II) ion has a regular square pyramidal geometry

(s = 0.04) and is coordinated to three monodentate ni-

trate ions and two water molecules. The axial position

is occupied by one oxygen atom from one nitrate anion

and the equatorial plane defined by the four oxygen

atoms has a r.m.s. value of 0.0367. The distance of the

Cu(2) atom from the O4 coordination plane is 0.0513(0.0029) A, indicating that the metal is barely out of

the plane. The O atom that occupies the axial position

is 2.294(8) A away from the metal and the average value

for the O4–Cu(2) bond distance is 1.97 A, which is typ-

ical for this kind of bond [20,21].

In contrast, the perchlorate ions in complexes 4 and 6

are not coordinated to the metal ion.

Both centroid–centroid and interplanar distances areused as criteria to determine whether a p,p-interactionexists between aromatic rings, with interplanar distances

Table 2

Selected bond lengths and angles at the M(II) atom

[CoL][Co(NO3)4] ÆCH3CN (1)

[NiL]( NO3)2 (3) [NiL](ClO4)2 Æ CH3CN Æ 3H2O (4) [CuL][Cu(NO3)3(H2O)2] Æ (NO3) Æ H2O (5) [CuL](ClO4)2 Æ 2CH3CN (6)

N(1)–Co(1) 2.044(2) N(1)–Ni(1) 2.010(2) N(1)–Ni(1) 2.007(6) N(1)–Cu(1) 1.974(5) N(1)–Cu(1) 1.981(13)






O(1N)–Co(2) 2.033(3) N(4)–Ni(1)–N(1) 179.85(12) N(4)–Ni(1)–N(1) 179.1(3) O(1W)–Cu(2) 1.968(5) N(4)–Cu(1)–N(1) 178.5(5)

O(4N)–Co(2)#1 2.108(3) N(4)–Ni(1)–N(2) 102.28(10) N(4)–Ni(1)–N(2) 102.2(2) O(2W)–Cu(2) 1.977(5) N(4)–Cu(1)–N(3) 78.7(5)

O(8N)–Co(2)#2 2.023(4) N(1)–Ni(1)–N(2) 77.76(10) N(1)–Ni(1)–N(2) 77.9(2) O(6N)–Cu(2) 1.972(5) N(1)–Cu(1)–N(3) 102.6(5)

O(9N)–Co(2)#2 2.366(6) N(4)–Ni(1)–N(3) 77.74(10) N(4)–Ni(1)–N(6) 103.1(2) O(7N)–Cu(2) 1.963(5) N(4)–Cu(1)–N(5) 77.7(5)

O(10N)–Co(2) 2.112(5) N(1)–Ni(1)–N(3) 102.41(10) N(1)–Ni(1)–N(6) 76.9(2) O(10N)–Cu(2) 2.294(8) N(1)–Cu(1)–N(5) 101.0(5)

N(2)–Ni(1)–N(3) 83.22(9) N(2)–Ni(1)–N(6) 154.8(2) N(4)–Cu(1)–N(1) 178.30(19) N(3)–Cu(1)–N(5) 156.4(4)

N(1)–Co(1)–N(4) 177.94(10) N(4)–Ni(1)–N(6) 102.99(9) N(4)–Ni(1)–N(5) 77.9(2) N(4)–Cu(1)–N(6) 101.07(18) N(4)–Cu(1)–N(6) 103.1(5)









N(3)–Co(1)–N(5) 153.15(9) N(4)–Cu(1)–N(3) 77.60(17)

N(1)–Co(1)–N(2) 76.54(9) N(1)–Cu(1)–N(3) 101.27(17)

N(4)–Co(1)–N(2) 102.48(10) N(6)–Cu(1)–N(3) 103.77(17)

N(6)–Co(1)–N(2) 153.79(9) N(2)–Cu(1)–N(3) 81.36(17)

N(3)–Co(1)–N(2) 82.87(9) N(5)–Cu(1)–N(3) 155.67(17)

N(5)–Co(1)–N(2) 103.46(9) O(7N)–Cu(2)–O(1W) 92.4(2)

O(8N)#2–Co(2)–O(1N) 111.60(13) O(7N)–Cu(2)–O(6N) 90.2(2)

O(8N)#2–Co(2)–O(4N)#3 120.32(15) O(1W)–Cu(2)–O(6N) 177.2(2)

O(1N)–Co(2)–O(4N)#3 97.78(12) O(7N)–Cu(2)–O(2W) 174.9(2)

O(8N)#2–Co(2)–O(10N) 140.98(18) O(1W)–Cu(2)–O(2W)87.6(2)

O(1N)–Co(2)–O(10N) 94.62(18) O(6N)–Cu(2)–O(2W)89.7(2)

O(4N)#3–Co(2)–O(10N) 81.95(13) O(7N)–Cu(2)–O(10N) 98.2(3)

O(8N)#2–Co(2)–O(9N)#2 55.57(16) O(1W)–Cu(2)–O(10N) 90.3(3)

O(1N)–Co(2)–O(9N)#2 162.87(18) O(6N)–Cu(2)–O(10N) 90.3(3)

O(4N)#3–Co(2)–O(9N)#2 82.06(15) O(2W)–Cu(2)–O(10N) 86.9(3)

O(10N)–Co(2)–O(9N)#2 102.3(2)

2624

L.Valen

ciaet

al./Inorganica

Chim

icaActa

358(2005)2618–2628

Fig. 3. ORTEP drawing of the molecular structure of the dication from 6, [CuL]2+.

Fig. 2. ORTEP drawing of the molecular structure of the dication from 4, [NiL]2+.


in the range 3.3–3.8 A commonly accepted for face to

face stacks of aromatic units with approximately paral-

lel molecular planes [16].

The crystal lattices of the cobalt(II) and nickel(II) ni-

trate complexes 1 and 3 contain nitrate ions that are sit-

uated close to the pyridine rings but are slightly tiltedwith respect to them. In these cases, the dihedral angles

between the planes are 18.09 (0.31)� and 14.76 (0.19)�for 1 and 3, respectively. In the copper(II) nitrate com-

plex 5, the nitrate ions are more tilted with respect to

the pyridine rings than in the other complexes and, in

this case, the dihedral angles are 44.39� and 45.69� [be-tween the nitrate ion of N2ni and the pyridine rings of

N1 and N4 (I = x, y � 1, z)].

Table 3 suggests the possibility of a p,p-stackinginteraction between nitrate ions and pyridine rings inthe crystal structure of complexes 1, 3 and 5.

In this case, we can consider the distance between the

centroid of the pyridine and the N atom of the nitrate

group as analogous to the centroid–centroid distance.

Fig. 4. ORTEP drawing of the molecular structure of: (a) [CoL][Co(NO3)4] Æ CH3CN (1); (b) [NiL](NO3)2 (3); (c) [CuL][Cu(NO3)3(H2O)2]

(NO3) Æ H2O (5), showing the intermolecular atom–atom distances [A] shorter than 3.5 A between nitrate ions and pyridine and nitrile groups.

Table 3

Intermolecular atom–atom distances [A] shorter than 3.5 A for 1, 3

and 5

[CoL][Co(NO3)4] ÆCH3CN (1)

[NiL](NO3)2] (3) [CuL][Cu(NO3)3(H2O)2(NO3) ÆH2O (5)

C11–O11n 3.221 C10–O2n 3.167 C13–O9n 3.247

C14–O12n 3.492 C11–O2n 3.148 N7–O9n 3.175

C13–O12n 3.526 C11–N1n 3.104 C14–O9n 3.346

C10–O11n 3.427 C10–N1n 3.423 N7–N3n 3.393

N10–O11n 3.394 C12–O3n 3.297 C4–O6n_$1 3.0815

N10–O2n 3.443 C2–O4N_$1 3.3764

C30–O2n 3.349 N9–N2N_$1 3.2392

$1 = x, y � 1, z.


]

This distance (dc–N) is 3.6, 3.4 and 3.5 A, respectively.

However, as these two planes are tilted, atom–atom con-

tacts provide a better criterion and supply more suitableinformation about possible contacts between these

groups. In all cases (see Table 3), the intermolecular

atom–atom distances are shorter than the sum of the

van der Waals radii for these atoms [22]. These results

reveal that p,p-interactions exist in these complexes be-

tween nitrate ions and pyridine fragments from the li-

gand L. Although a CSD search reveals that this sort

of p,p-interaction between pyridine rings and nitrateions is present in previously reported structures


[23,24], to the best of our knowledge, it was not previ-

ously described in the literature. Only Sanchez-Moreno

et al. [25] reported nitro-benzyl p,p-interactions in two

mixed Cu(II) complexes with N-(p-nitrobenzyl)iminodi-

acetic acid (NBIDA).

Table 3 also contains some atom–atom distances be-tween the nitrate ions and the nitrile groups on the pen-

dants present in the ligand. These distances are shorter

than the sum of the van der Waals radii for these atoms,

again suggesting an interaction between the nitrate ion

and the p-shell of the nitrile pendant group, which has

not been described either in the literature, although a

new CSD search reveals the existence of that in some

deposited crystal structures [26].

5. Spectroscopic and magnetic studies

The IR spectra of the complexes were recorded using

KBr discs. The spectra exhibit medium to strong bands

at ca. 1610, 1580 and 1470 cm�1, as expected for the

m(C@C) and m(C@N) pyridine ring vibrations. Thesebands are shifted to higher wavenumbers when com-

pared to those in the free ligand, suggesting coordina-

tion to the metal atom [27,28].

Perchlorate complexes exhibit a medium intensity

band in the region 2248–2253 cm�1 and this is attributed

to the m(C„N) mode of the pendant groups. These

bands are in the same position as in the free ligand L

spectrum, indicating that coordination of the nitrilegroups to the metal does not occur. On the other hand,

the IR spectra of the nitrate complexes show in all cases

two equal intensity bands at 2251 and 2426 cm�1. The

2251 cm�1 band is similar to the free ligand vibration

(2245 cm�1). However, the presence of the second band

(2426 cm�1) is surprising given that the crystal struc-

tures do not show any interaction between the nitrile

groups and the metal ions. The presence of this secondband only in the nitrate complexes is consistent with

the p,p-interaction shown in the solid state structure

of the nitrate complexes between those counterions

and the nitrile groups. The crystal structures of 1, 3

and 5 reveal the presence of a p,p-interaction between

the nitrate ions and the pyridine rings. These nitrate ions

were in all complexes in a middle position between the

pyridine ring and one nitrile pendant group, a situationthat could even give rise to an interaction between these

three p-systems. The shortest atom–atom distances are

reported in Table 3.

The IR spectra of the perchlorate complexes feature

absorptions attributable to ionic perchlorate at

1100 cm�1. The lack of splitting of this band indicates

that these groups are not coordinated to the metal cen-

tres [29,30]. However, the IR spectra of the nitrate com-plexes show the presence of several bands in the region

associated with nitrate vibrations, indicating the pres-

ence of coordinated nitrate groups. In addition, all spec-

tra show the presence of the vibration associated with

ionic nitrate groups at 1383 cm�1 [31].

The solid state electronic spectra were obtained at

room temperature for all complexes. The reflectance

spectrum of [CoL](ClO4)2 Æ 4H2O (2) shows two d–dtransition bands at ca. 10838 and 16666 cm�1, which

are due to the 4T2g 4T1g and4T1g(P) 4T1g(F) transi-

tions, respectively, and are of the type expected for dis-

torted octahedral high spin Co(II) complexes [32]. In the

case of [CoL][Co(NO3)4] Æ CH3CN (1), the spectrum is

complicated and shows five bands at 8636, 15300,

18000, 19685 and 21552 cm�1. These bands must be

attributable to the presence of both octahedral and a tri-gonal bipyramidal arrangement for the Co(II) ions [33].

The reflectance spectra of the nickel complexes

[NiL](NO3)2 (3) and [NiL](ClO4)2 Æ CH3CN Æ 3H2O (4)

show three bands at ca. 10415, 17540 and

31250 cm�1. These bands are attributable to the3T2g 3A2g,

3T1g(F) 3A2g and3T1g(P) 3A2g tran-

sitions, respectively, and are indicative of octahedral

Ni(II) compounds. One absorption band at ca.15150 cm�1is also present and is probably due to the

spin forbidden transition 1Eg 3A2g usually observed

in Ni(II) complexes [34].

The X-ray structure of [CuL][Cu(NO3)3(H2O)2] Æ(NO3) Æ H2O (5) shows two metal ions having different

coordination numbers and geometries. In [CuL]

(ClO4)2 Æ 2CH3CN (6), the solid state structure shows a

mononuclear complex in a distorted octahedral environ-ment, but no difference was found in the solid state UV–

vis spectra of these two complexes. The UV spectra

show a broad band with a maximum at 13570 cm�1and

a shoulder at 7350 cm�1, which are typical of octahedral

Cu(II) complexes [35].

The values of the room temperature magnetic mo-

ments of the compounds [CoL](ClO4)2 Æ 4H2O (4.8

BM), [NiL](NO3)2(2.9 BM), [NiL](ClO4)2 Æ CH3CN Æ3H2O (2.8 BM) and [CuL](ClO4)2 Æ 2CH3CN (1.8 BM)

lie within the range usually observed for high-spin octa-

hedral Co(II), and octahedral Ni(II) and Cu(II) com-

plexes. The magnetic moment values obtained for

[CoL][Co(NO3)4] Æ CH3CN and [CuL][Cu(NO3)3(H2O)2] Æ (NO3) Æ H2O are 8.3 and 3.4 BM, respectively.

These values are consistent with the presence of high

spin octahedral and pentacoordinated Co(II) and Cu(II)ions [36].

6. Conclusion

The new macrocyclic ligand L, which contains two

pyridine rings in the ligand skeleton and bears four

cyanoethyl pendant groups, has been synthesized byreaction of the precursor L1 with acrylonitrile. In the

solid state, L presents a nanotubular structure arranged


by p,p-stacking interactions between the pyridine

groups. The complexation capacity of the ligand L to-

ward a range of first row transition metals has been stud-

ied. The crystal structures of [CoL][Co(NO3)4] Æ CH3CN

(1), [NiL](NO3)2 (3), [NiL] (ClO4)2 Æ CH3CN.3H2O (4),

[CuL][Cu(NO3)3(H2O)2] (NO3) Æ H2O (5) and [CuL](ClO4)2 Æ 2CH3CN (6) were determined, and in all cases

the dication [ML]2+ is present. The X-ray structure of

the nitrate complexes reveals a new and unexpected

simultaneous p,p-interactions between a pyridine ring,

a nitrate ion and a nitrile group.

7. Supplementary material

Crystallographic data (excluding structure factors) for

the structures reported in this paper have been deposited

with the Cambridge Crystallographic Data Centre as

supplementary publication: CCDC 234001 for L, CCDC

234002 for [CoL][Co(NO3)4] Æ CH3CN, CCDC 234003

for [NiL](NO3)2, CCDC 234004 for [NiL](ClO4)2 ÆCH3CN Æ 3H2O, CCDC 234005 for [CuL][Cu(NO3)3-(H2O)2](NO3) Æ H2O and CCDC 234006 for [CuL]-

(ClO4)2 Æ 2CH3CN. Copies of the data can be obtained

free of charge on application to the Cambridge Crystal-

lographic Data Centre, 12 Union Road, Cambridge CB2

IEZ, UK [fax: (internat.) +44 (0)1223 336033; e-mail:

[email protected]].

Acknowledgements

We thank Xunta de Galicia (PGIDT01PXI20901PR)

for financial support. Intensity measurements were per-

formed at the Unidade de Raios X. RIAIDT. University

of Santiago de Compostela, SPAIN.

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Documents

Co (II), Ni(II) and Cu(II) complexes with a new pendant armed macrocyclic ligand showing several π,π-interactions