Inorganica Chimica Acta 363 (2010) 995–1000

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Inorganica Chimica Acta

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Extended molecular networks based on Zn and Cd impartingN-substituted imidazole

Ashish Kumar Singh a, Mahendra Yadav a, Sanjay Kumar Singh a, Sailaja Sunkari b, Daya Shankar Pandey a,*

a Department of Chemistry, Faculty of Science, Banaras Hindu University, Varanasi 221 005, Indiab Mahila Mahavidyalaya, Banaras Hindu University, Varanasi 221 005, India

a r t i c l e i n f o a b s t r a c t

Article history:Received 12 June 2009Received in revised form 30 November 2009Accepted 10 December 2009Available online 16 December 2009

Keywords:ZincCadmium1-(4-Cyanophenyl)-imidazoleCrystal structureWeak interactions

0020-1693/$ - see front matter � 2009 Elsevier B.V. Adoi:10.1016/j.ica.2009.12.025

* Corresponding author. Tel.: +91 542 7602480.E-mail address: dspbhu@bhu.ac.in (D.S. Pandey).

Synthesis of complexes with the formulations [M(CPI)2Cl2] (M = Zn, 1; M = Cd, 4) and [M(CPI)6](X)2

(M = Zn, X = NO3�, 2; X = ClO4

�, 3; M = Cd, X = NO3�, 5; X = ClO4

�, 6) have been achieved from the reac-tions of MCl2, M(NO3)2�xH2O and M(ClO4)2�xH2O (M = Zn, Cd) with 1-(4-cyanophenyl)-imidazole (CPI).Complexes 1–6 have been characterized by elemental analyses and spectral studies (IR, 1H, 13C NMR,electronic absorption and emission). Molecular structures of 1, 2, 3 and 6 have been determined crystal-lographically. Weak interaction studies on the complexes revealed presence of various interesting motifsresulting from C–H���N, C–H���Cl and p–p stacking interactions. The complexes under study exhibit strongluminescence at �450 nm in DMSO at room temperature.

� 2009 Elsevier B.V. All rights reserved.

1. Introduction

Hectic activity has been shown by various research groups to-wards the design and construction of nanoporous supramolecularsystems [1–3]. In self-organization of the metal complexes tosupramolecular architectures with well-defined shapes and func-tions, several type of forces such as coordination bonding, hydro-gen bonding, p–p stacking and electrostatic interactions playcrucial roles [4–8]. Among these forces, coordination bondingand hydrogen bonding interactions are most important. The under-standing and utilization of all non-covalent interactions, includingp–p stacking, is of fundamental importance for the further devel-opment of inorganic supramolecular chemistry and the tuningand prediction of crystal structures [9]. The metal ion and counterions (anions) present in the system which behave as Lewis acid andbases, respectively strongly affect the strength of intermolecularinteractions and ordering of the crystal lattice [10,11].

Self-assembly methods involving polydentate organic ligandscontaining N- or O-donor atoms as building blocks are generallyemployed in the synthesis of novel multi-functional materials[12–15]. In this regard, imidazole and ligands based on it havedrawn special attention owing to their good coordination abilityand diverse coordination modes [16–19]. Cyanide is another ligandthat have been studied by inorganic chemists and like imidazolehave been employed in the construction of extended structures

ll rights reserved.

[20,21]. Literature survey revealed that ligands containing boththe imidazole and cyanide group have not been utilized in the con-struction of functional extended networks. 1-(4-cyanophenyl)-imidazole (CPI), containing both the imidazole and cyanide groupserves as an unsymmetrical bridging ligand [22,23]. Adoption ofan unsymmetrical bridging ligand like CPI is expected to give abroader palette of extended structures than can be achieved withsymmetrical ligands. Further, the CN group of CPI may undergohydrolysis to form 4-(imidazolyl)-benzoic acid, another unsym-metrical ligand that have been used in the construction of interest-ing networks [24–26].

In a follow-up of our studies on ligational properties of CPIwith d-block metal centers, we have carried out its reactions withmetal salts and have isolated self-assembled systems arising fromweak bonding interactions [27–29]. Herein, we present spectralproperties and structures of some novel molecular species withthe formulations [M(CPI)2Cl2] (M = Zn, 1; M = Cd, 4) and[M(CPI)6](X)2 (M = Zn, X = NO3

�, 2, X = ClO4�, 3; M = Cd,

X = NO3�, 5, X = ClO4

�, 6).

2. Experimental

2.1. Materials and methods

The solvents and reagents employed in the experiments wereused as received. The ligand 1-(4-cyanophenyl)-imidazole (CPI)was prepared and purified following literature procedures[22]. C, H and N analyses on the samples were performed Exeter

996 A.K. Singh et al. / Inorganica Chimica Acta 363 (2010) 995–1000

Analytical Inc. Model CE-440 Elemental Analyzer. IR in KBr discsand electronic absorption spectra in DMSO were acquired on a Shi-madzu-8201PC and Shimadzu-UV-1700 spectrophotometers,respectively. 1H and 13C NMR spectra were obtained on JEOL300 MHz NMR instrument using TMS as an internal reference.Emission spectra were recorded on a Perkin–Elmer LS-45 lumines-cence spectrophotometer at room temperature.

2.2. Syntheses of complexes

Following general procedure was adopted for the synthesis ofcomplexes 1–6. In a typical reaction, metal salt (1.0 mmol) andCPI (2.0 mmol) in 10 ml water–ethanol mixture (4:1) were heatedin a sealed tube in an oil-bath at 120 �C for 72 h. After cooling toroom temperature diffraction quality crystals were directly ob-tained from the reaction mixture. These were separated, washedwith ethanol, diethyl ether and dried under vacuum. Selected dataof the complexes are given below:

2.2.1. Characterization data of [Zn(CPI)2Cl2] (1)Yield of ca. 65% (0.308 g). Anal. Calc. for 1 (C20H14N6Cl2Zn): C,

50.63; H, 2.95; N, 17.72. Found: C, 50.39; H, 2.86; N, 17.63%. IR(cm�1): 2953, 2856, 2224.13 (vs), 1610 (vs), 1523 (vs), 1462 (vs),1377 (s), 1307 (vs), 1261 (s), 1184 (w), 1122 (w), 1064 (s), 964(w), 943 (w), 875 (w), 833 (vs), 742 (s), 648 (s), 623 (w), 569 (w),553 (s), 480 (w). 1H NMR (DMSO, d ppm): 7.22 (s, 1H), 7.94 (s,1H), 7.98 (d, 2H, J = 6.6 Hz), 8.04 (d, 2H, J = 6.3 Hz), 8.57 (s, 1H).13C NMR (DMSO, d ppm): 112.6 (CN), 116.9, 122.1, 123.8, 127.6,132.5, 139.2, 145.2.

2.2.2. Characterization data of [Zn(CPI)6](NO3)2 (2)Yield of ca. 67% (0.268 g). Anal. Calc.for 2 (C60H42N20O6Zn): C,

59.78; H, 3.49; N, 23.17. Found: C, 59.23; H, 3.49; N, 23.28%. IR(cm�1): 2953 (vbr), 2227 (vs), 1763 (w), 1606 (vs), 1520 (s), 1458(s), 1379 (br), 1249 (s), 1116 (s), 1062 (s), 962 (w), 927 (w), 823(vs), 752 (s), 671 (w), 653 (w), 559 (w), 432 (w). 1H NMR (DMSO,d ppm): 7.46 (d, 1H, J = 7.2 Hz), 7.72 (d, 2H, J = 6.9 Hz), 7.86 (d,2H, J = 9.3 Hz), 7.97 (d, 2H, J = 9.0 Hz). 13C NMR (DMSO, d ppm):112.6 (CN), 116.9, 122.1, 123.8, 127.6, 132.5, 139.2, 145.2.

2.2.3. Characterization data of [Zn(CPI)6](ClO4)2 (3)Yield of ca. 61% (0.277 g). Anal.Calc. for 3 (C60H42N18O8Cl2Zn): C,

56.27; H, 3.28; N,19.69. Found: C, 56.06; H, 3.12; N, 19.40%. IR

N

N

N

MCl

ClN

N

N

N

NC

NC

[M(H2O)

M=Zn(1) Cd(4)

MCl2

Scheme 1. Preparation

(cm�1); 3391 (vbr), 2897 (br), 2395 (m), 2227.98 (vs), 1763 (w),1606 (vs), 1518 (s), 1467 (s), 1379 (br), 1304 (vs), 1253 (vs),1186 (w), 1091 (vs), 960 (w), 927 (w), 823 (s), 754 (s), 671 (w),655 (w), 623 (s), 557 (w), 432 (w). 1H NMR (DMSO, d ppm): 7.34(s, 1H), 7.73 (m, 2H), 7.92 (d, 2H, J = 8.1 Hz), 8.15 (d, 1H,J = 8.4 Hz), 8.46 (s, 1H). 13C NMR (DMSO, d ppm): 111.5 (CN),117.8, 121.4, 132.4, 133.2, 134.1, 137.1, 139.2.

2.2.4. Characterization data of [Cd(CPI)2Cl2] (4)Yield of ca. 56% (0.292 g). Anal. Calc. for 4 (C20H14N6Cl2Cd): C,

46.06; H, 2.70; N, 16.11. Found: C, 45.86.39; H, 2.86; N, 16.04%.IR (cm�1): 3339, 3198, 3118, 2923, 2857, 2230.5 (vs), 1610 (vs),1520 (vs), 1374 (s), 1307 (vs), 1267 (s), 1188 (w), 1116 (w), 1064(s), 961 (w), 835 (vs), 754 (s), 653 (s), 553 (s). 1H NMR (DMSO, dppm): 7.17 (s, 1H), 7.93 (m, 3H), 8.01 (d, 2H, J = 6.6 Hz), 8.46 (s,1H). 13C NMR (DMSO, d ppm): 112.5 (CN), 117.6, 122.8, 131.2,132.5, 134.7, 137.8, 138.2.

2.2.5. Characterization data of [Cd(CPI)6](NO3)2 (5)Yield of ca. 57% (0.238 g). Anal. Calc. for 5 (C60H42N20O6Cd): C,

57.50; H, 3.38; N, 22.36. Found: C, 57.23; H, 3.25; N, 22.28%. IR(cm�1): 3400 (br), 3133 (s), 2235.4 (vs), 1656 (w), 1608 (vs),1524 (s), 1379 (br), 1185 (s), 1121 (s), 1064 (s), 960 (w), 839(vs), 742 (s), 657 (w), 556 (w). 1H NMR (DMSO, d ppm): 7.32 (s,1H), 7.71 (m, 2H), 8.01 (d, 2H, J = 7.2 Hz), 8.32 (d, 1H, J = 6.9 Hz)8.46 (s, 1H). 13C NMR (DMSO, d ppm): 113.5 (CN), 118.6, 123.5,131.3, 132.9, 134.4, 138.1, 138.7.

2.2.6. Characterization data of [Cd(CPI)6](ClO4)2 (6)Yield of ca. 53% (0.234 g). Anal.Calc. for 6 (C60H42N18O8Cl2Cd): C,

54.29; H, 3.19; N,19.01. Found: C, 53.99; H, 3.09; N, 18.94%. IR(cm�1); 3317 (vbr), 3212 (s), 3121 (br), 2230.9 (vs), 1609 (vs),1521 (s), 1425 (s), 1373 (br), 1308 (vs), 1268 (vs), 1188 (w),1118 (s), 1065 (vs), 962 (w), 838 (s), 753 (s), 655 (w), 552 (w).1H NMR (DMSO, d ppm): 7.32 (s, 1H), 7.71 (m, 2H), 8.01 (d, 2H,J = 7.2 Hz), 8.32 (d, 1H, J = 6.9 Hz), 8.46 (s, 1H). 13C NMR (DMSO, dppm): 114.3 (CN), 115.2, 121.6, 130.9, 131.9, 135.1, 138.4, 140.2.

2.3. Crystallographic measurements

Crystals suitable for single crystal X-ray diffraction analyses for1–3 and 6 were obtained directly from the reaction mixture. Preli-minary data on the space group and unit cell dimensions as well as

M

N

NN

NN

NN

N

NN

N

N

NC

NC

CN

CN

CN

NC

6]X2

(X)2

M=Zn, X=NO3(2) X=ClO4(3)M=Cd, X=NO3(5) X=ClO4(6)

of complexes 1–6.

A.K. Singh et al. / Inorganica Chimica Acta 363 (2010) 995–1000 997

intensity data were collected on OXFORD DIFFRACTION X CAUBER-S for complexes 1 and 2, and on a BRUKER SMART APEX diffractom-eter for 4 and 6 using graphite monochromatized Mo Ka radiation.The structures were solved by direct methods and refined by usingSHELX-97 [30]. The non-hydrogen atoms were refined with aniso-tropic thermal parameters [31]. All the hydrogen atoms were geo-metrically fixed and allowed to refine using a riding model.

3. Results and discussion

The complexes 1–6 were obtained by heating respective metalsalts (1.0 mmol) with CPI (2.0 mmol) in water–ethanol mixture10 ml (4:1) in a sealed tube at 120 �C for 72 h. Upon cooling toroom temperature diffraction quality crystals were obtained from

Fig. 1. Molecular structure of 1 at 30% probability (hydrogen atoms omitted forclarity). Selected bond lengths (Å) and angles (�): Zn(1)–N(1) = 2.0242(13), Zn(1)–Cl(1) = 2.2414(5), N(1)–Zn(1)–N(1) = 107.25(8), N(1)–Zn(1)–Cl(1) = 115.20(4),N(1)–Zn(1)–Cl(1) = 103.51(4), Cl(1)–Zn(1)–Cl(1) = 112.45(3). Symmetry operation:(i) �x + 2, y, �z + 1/2.

Fig. 2. Zig-zag chain in 1 arising from

the reaction mixture. A simple scheme showing synthesis of thecomplexes is depicted in Scheme 1. Geometrical formulations ofthe complexes were established by elemental analyses, spectralstudies and structures of 1–3 and 6 have been authenticated crys-tallographically. Selected characterization data of the complexes issummarized in the Supplementary material.

Infra-red spectra of the complexes exhibited characteristicbands corresponding to mC„N and mC@N of the coordinated CPI at�2220 and �1600 cm�1, respectively [22]. The band associatedwith imidazole ring vibrations exhibited a shift towards lower en-ergy side and appeared at �1600 cm�1 as compared to that in thefree ligand (1610 cm�1). Shift in the position of mC@N suggestedlinkage of the ligand CPI to the metal center through imidazolenitrogen.

Presence of resonances associated with CPI in the NMR spectraof respective complexes suggested coordination of CPI to therespective metal center. 1H and 13C NMR spectra of the complexesdisplayed a general trend where protons associated with CPI reso-nated in the aromatic region between 7.20 and 8.50 ppm, whilecarbons at �115.0–139.0 ppm. Nitrile carbon of the coordinatedCPI resonated at �110 ppm. Further, it was observed that the sig-nals associated with various protons and carbons of the ligand dis-played an insignificant shift in comparison to the uncoordinatedCPI, it may be attributed to the poor donation from ligand-to-metalcenter [22].

Molecular structures of 1, 2, 3 and 6 have been determined crys-tallographically. Selected crystallographic data is summarized inTable S1 and crystal structure of 1 and cation of 2, 3 and 6 (iso-structural) is depicted in Figs. 1 and 3. Selected geometrical param-eters are recorded below the crystal structures.

Coordination geometry about Zn(II) in complex 1 may be de-scribed as distorted tetrahedral with N2Cl2 donor groups. Imidaz-olyl nitrogen of the CPI occupies two sites about Zn(II), while othertwo positions are occupied by the chloro groups. Various anglesabout the metal center are close to tetrahedral systems with smalldeviations. Zn–N and Zn–Cl distances are 2.0242(13) and2.2414(5) Å, respectively. These are comparable to those in other

p–p and C–H���N interactions.

Fig. 3. General representation of the cation of 2, 3 and 6 at 30% probability(hydrogen atoms omitted for clarity). Selected bond lengths (Å) and angles (�):Zn(1)–N1 = 2.1952(19), N1–Zn1–N1 = 180.0, N(1)–Zn(1)–N(1) = 92.58(7), N(1)–Zn(1)–N(1) = 87.42(7), 2; Zn(1)–N1 = 2.190(3), N(1)–Zn(1)–N(1) = 180.0, N(1)–Zn(1)–N(1) = 92.10(12), N(1)–Zn(1)–N(1) = 87.90(12), 3; Cd(1)–N(1) = 2.3617(18),N(1)–Cd(1)–N(1) = 180.0, N(1)–Cd(1)–N(1) = 94.06(6), N(1)–Cd(1)–N(1) = 85.94(6),6.

Table 1Separation between layers and distances as assigned in Fig. 4.

Intra-layerseparation

Inter-layerseparation

Phenyl ring center tocenter separation(inter-/intra-layer)(c/d)

Imidazole ringcenter tocenterseparation (e)

Complex2

3.436 3.597 3.635/3.925 3.876

Complex3

3.479 3.633 3.669/3.977 3.948

Complex6

3.361 3.514 3.608/3.803 3.747

998 A.K. Singh et al. / Inorganica Chimica Acta 363 (2010) 995–1000

Zn(II) imidazole complexes [32–36]. The cyanophenyl ring istwisted with respect to imidazole ring so that CPI is non-planar.Dihedral angle between the phenyl and imidazole ring planes are21.2(2)�.

Packing in complex 1 along crystallographic ‘c’-axis leads tocrown shaped motif (Fig. S1). Weak bonding interactions betweennitrile nitrogen and C6 hydrogen [distance 2.635(3) Å] gives rise tounique 1D zig-zag chain along crystallographic ‘a’-axis in [bc] plane(Fig. 2 and Fig. S2) with a pitch of 28.119 Å. Each chain is stabilizedby p–p interactions between phenyl rings of the adjacent chainswith center to center separation of 3.289 Å (Fig. 2).

Structural studies revealed that the complexes 2, 3 and 6 areisostructural. A common structural feature of 2, 3 and 6 is that eachof them are composed of discrete [M(CPI)6]2+ cations and counterions (NO3

� or ClO4�). Site occupancy of the counter ions are twice

of the metal, which suggested that corresponding to each metal ionthere are two counter ions consistent with the electro-neutrality ofthe compounds. The metal cation occupies an inversion center.Overall geometry about the metal centres is octahedral with MN6

environment wherein six N donors are derived from imidazolenitrogen of six different CPI. These six CPI ligands are distributed

Fig. 4. p–p stacking between phenyl a

alternately in two parallel planes about the metal centres in sucha way that the cation has approximately D3d symmetry (Fig. 3).The M–N bond distances [Zn–N = 2.195(19), 2; Zn–N = 2.190(3),3; Cd–N = 2.3617(18), 6] are in the normal range for respectiveM–N distances [32–37]. The cyanophenyl rings are twisted (TableS2) with respect to imidazole ring within each of these ligands.

Intermolecular p–p interactions have been employed in theconstruction of coordination networks from discrete molecules(Fig. 4) [38]. Complexes 2, 3 and 6 are unique in the sense that,although these are mononuclear complexes overall layered struc-tures have been observed for each of them (Table 1). Intermolecu-lar face-to-face p–p interactions between discrete [M(CPI)6]2+

moieties involving cyanophenyl rings of the CPI results in a 2Drim (molecular wheel) and pendent ring like motif along crystallo-graphic ‘c’-axis (Fig. 5). Layers are almost parallel to each other(Fig. 4 and Figs. S3 and S4). The sheets align in an eclipsed fashionalong crystallographic ‘a’-axis through aromatic face-to-face p–pstacking interactions leading to a AAA packing motif containing tri-angular channels occupied by counter ions (Fig. 5a and Fig. S4).Non-covalent interactions are analogous in these complexes withslight difference due to counter ion nitrate and perchlorate. In[Zn(CPI)6](NO3)2, nitrate anions are disordered.

During course of this study we came across several interestingobservations. It was observed that that metal salt employed inthe reaction plays an important role towards formation of finalproduct. For example, reactions of CPI with ZnCl2/CdCl2 affordedtetrahedral complexes 1 and 4, while its reaction with hexahydratesalts [M(H2O)6]X2 (M = Zn, Cd) (X = NO3

�, ClO4�) under analogous

conditions afforded molecular species [M(CPI)6](X)2 suggestingcounter-anion produces strong template effect. Further, water ofcrystallization present in the metal salt also plays an importantrole. In the synthesis of 2, 3 and 5, 6 we found that whether thereaction was carried out in 1:2 molar ratio or in presence of an ex-cess CPI, final product remains the same. In some of the reactionsalong with CPI a good linker like 4,40-bipyridine was also used.To our surprise we could not get any extended network containing

nd imidazole rings in 2, 3 and 6.

Fig. 5. (a) Wheel motif resulting from intra-layer p–p stacking (b) Pendent ring motif resulting from inter-layer p–p stacking.

Fig. 6. Emission spectra of complexes 1–6.

A.K. Singh et al. / Inorganica Chimica Acta 363 (2010) 995–1000 999

4,40-bipyridine, rather it afforded the molecular species[Zn(CPI)6](X)2 (X = NO3

�, ClO4�). Formation of 2 and 3 in presence

of a strong linker over the formation of extended networks con-taining linkers may be attributed to high stability of the molecularspecies [M(CPI)6](X)2 (M = Zn, Cd), arising from face-to-face p–pinteractions between co-planar molecules.

The photoluminescence properties of 1–6 were studied inDMSO at room temperature. Measurements were carried out underanalogous conditions. Resulting data is summarized in Table S3 andcomparative spectrum is depicted in Fig. 6. Interestingly, all thecomplexes upon excitation at 280–283 nm exhibited luminescencewith emission maxima centered at 433–444 nm. It is analogous tothat observed in the ligand CPI (emission maximum at 438 nmupon excitation at 284 nm) (Table S3). The emissions observed inthese complexes have been tentatively assigned to the p–p* in-tra-ligand fluorescence due to their close resemblance with theemission bands in CPI [22]. These emissions are neither metal-to-ligand charge transfer (MLCT) nor ligand-to-metal charge transfer(LMCT) in nature, because Zn(II)/Cd(II) ions are difficult to oxidizeor to reduce (d10 configuration) [20].

4. Conclusions

Through this study we have developed some novel self-assem-bled systems based on Zn and Cd imparting unsymmetrical bridg-ing ligand 1-(4-cyanophenyl)-imidazole. It has been shown thatmetal salt employed in the reaction, counter ion and water of crys-tallization present in the metal salt strongly influences nature ofthe final product. Formation of molecular species [M(CPI)6](X)2

(M = Zn, Cd) over extended networks containing linkers in pres-ence of a strong linker arises from face-to-face p–p interactions be-tween co-planar molecules.

Acknowledgements

Thanks are due to the Department of Science and Technology,New Delhi, India for providing financial assistance through thescheme SR/S1/IC-15/2006. One of the authors (A.K.S.) acknowl-edges CSIR, New Delhi for awarding JRF (Award No. 09/013(0127)/2007, EMR-I). The authors are also grateful to the HeadDepartment of Chemistry, Faculty of Science, Banaras Hindu Uni-versity, Varanasi (UP) for extending facilities. Special thanks aredue to Prof. Pradeep Mathur, In-charge, National Single Crystal X-ray Diffraction Facility, Indian Institute of Technology, Mumbai, In-dia for providing single crystal X-ray data.

Appendix A. Supplementary material

CCDC 702825, 702826, 702827 and 702830 contain the supple-mentary crystallographic data for 1, 2, 3 and 6, respectively. Thesedata can be obtained free of charge from The Cambridge Crystallo-graphic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.Supplementary data associated with this article can be found, inthe online version, at doi:10.1016/j.ica.2009.12.025.

References

[1] S.S.Y. Chui, S.M.F. Lo, J.P.H. Charmant, A.G. Orpen, I.D. Williams, Science 283(1999) 1148.

[2] E. Coronado, J.R. Galan-Mascaros, C.J. Gomez-Garcia, C. Laukhin, Nature 408(2000) 447.

[3] W. Schmitt, J.P. Hill, M.P. Juanico, A. Caneschi, F. Costantino, C.E. Anson, A.K.Powell, Angew. Chem. 117 (2005) 4259. Angew. Chem., Int. Ed. 44 (2005) 4187.

[4] H.W. Roesky, M. Andruh, Coord. Chem. Rev. 236 (2003) 91.[5] J.D. Dunitz, A. Gavezzotti, Angew. Chem., Int. Ed. 44 (2005) 1766.

1000 A.K. Singh et al. / Inorganica Chimica Acta 363 (2010) 995–1000

[6] S. Kammer, H. Müller, N. Grunwald, A. Bellin, A. Kelling, U. Schilde, W. Mickler,C. Dosche, H.-J. Holdt, Eur. J. Inorg. Chem. (2006) 1547.

[7] G.R. Desiraju, Acc. Chem. Res. 35 (2002) 565.[8] M.E. Devis, Nature 417 (2002) 813.[9] C. Janiak, J. Chem. Soc., Dalton Trans. (2000) 3885.

[10] J.W. Steed, J.L. Atwood, Supramolecular Chemistry, John Wiley and Sons,London, 2000 (Chapter 4).

[11] P.D. Beer, P.A. Gale, Angew. Chem., Int. Ed. 40 (2001) 486.[12] H. Li, M. Eddaoudi, M. O’Keeffe, O.M. Yaghi, Nature 402 (1999) 276.[13] S.S.-Y. Chui, S.M.-F. Lo, J.P.H. Charmant, A.G. Orpen, I.D. Williams, Science 283

(1999) 1148.[14] J. Kim, B. Chen, T.M. Reineke, H. Li, M. Eddaoudi, D.B. Moler, M. O’Keeffe, O.M.

Yaghi, J. Am. Chem. Soc. 123 (2001) 8239.[15] N.L. Rosi, J. Eckert, M. Eddaoudi, D.T. Vodak, J. Kim, M. O’Keeffe, O.M. Yaghi,

Science 300 (2003) 1127.[16] N. Masciocchi, G.A. Ardizzoia, G. LaMonica, A. Maspero, S. Galli, A. Sironi, Inorg.

Chem. 40 (2001) 6983.[17] N. Masciocchi, F. Castelli, P.M. Forster, M.M. Tafoya, A.K. Cheetham, Inorg.

Chem. 42 (2003) 6147.[18] S.J. Rettig, A. Storr, D.A. Summers, R.C. Thompson, J. Trotter, J. Am. Chem. Soc.

119 (1997) 8675.[19] J. He, J.-X. Zhang, G.-P. Tan, Y.-G. Yin, D. Zhang, M.-H. Hu, Cryst. Growth Des. 7

(2007) 1508.[20] K.R. Dunbar, R.A. Heintz, Progress in Inorganic Chemistry, vol. 45, John Wiley

and Sons, New York, 1997, p. 283.[21] J.S. Miller, J.L. Manson, Acc. Chem. Res. 34 (2001) 563.[22] A. Hatzidimitriou, A. Gourdon, J. Devillers, J.-P. Launay, E. Mena, E. Mouyal,

Inorg. Chem. 35 (1996) 2212.

[23] A. Szemik-Hojniak, G. Balkowski, G.W.H. Wurpel, J. Herbich, J.H. VanderWaals,W.J. Buma, J. Phys. Chem. A 108 (2004) 10623.

[24] X.-M. Zhang, Coord. Chem. Rev. 249 (2005) 1201.[25] J.-Z. Zhang, W.-R. Cao, J.-X. Pan, Q.-W. Chen, Inorg. Chem. Commun. 10 (2007)

1360.[26] J.-Z. Zhang, J.-X. Pan, W.-R. Cao, Q.-W. Chen, Acta Crystallogr., Sect. E 63 (2007)

m1042.[27] S.K. Singh, M. Trivedi, M. Chandra, A.N. Sahay, D.S. Pandey, Inorg. Chem. 43

(2004) 26.[28] S.K. Singh, M. Trivedi, M. Chandra, D.S. Pandey, J. Organomet. Chem. 690

(2005) 647.[29] A.K. Singh, M. Yadav, P. Kumar, S.K. Singh, S. Sunkari, D.S. Pandey, J. Mol. Struct.

935 (2009) 1.[30] G.M. Sheldrick, SHELXL 97, Program for Refining Crystal Structures, University of

Gottingen, Germany, 1997.[31] G.M. Sheldrick, SHELXS 97, Program for the Solution of Crystal Structures,

University of Gottingen, Germany, 1990.[32] W.L. Steffen, G.J. Palenik, Inorg. Chem. 17 (1978) 1338.[33] C.I.H. Ashby, C.P. Cheng, E.N. Duesler, T.L. Brown, J. Am. Chem. Soc. 30 (1978)

6063.[34] E. Kimura, Y. Kurogi, M. Shionoya, M. Shira, Inorg. Chem. 30 (1991) 4524.[35] X.-M. Chen, Z.-T. Xu, X.-C. Huang, J. Chem. Soc., Dalton Trans. (1996) 3465.[36] A. Abufarag, H. Vahrenkamp, Inorg. Chem. 34 (1995) 2207.[37] C.A. Hester, H.L. Collier, R.G. Baughman, Polyhedron 15 (1996) 4255.[38] J. Jia, A.J. Blake, N.R. Champness, P. Hubberstey, C. Wilson, M. Schroder, Inorg.

Chem. 47 (2008) 8652.