Regioselective Coordination toward Silver(I) Ions by Bis- and Tris(Tetra-Armed Cyclen)s via Differential Electron Density of Aromatic Side Arms.

Four types of bis- and tris(tetra-armed cyclen)s were prepared. 2MF is a bis(tetra-armed cyclen) with electron-rich side arms (three 4-methoxybenzyl groups) and electron-deficient side arms (three 3,5-difluorobenzyl groups), connected by a 4,4'-dimethyl-1,1'-biphenyl moiety. 3MFM is a tris(tetra-armed cyclen) with 4-methoxybenzyl and 3,5-difluorobenzyl groups introduced on both ends and the central cyclen, respectively. 4MFM is a V-shaped analogue of 3MFM. 3FMF is a tris(tetra-armed cyclen) where the aromatic side arms at both ends and the central cyclen of 3MFM are exchanged. The regioselective coordination of silver(I) ions by these ligands is reported. Initially, we added Ag+ ions to a compound (2MF) that consists of tetra-armed cyclen with 4-methoxybenzyl groups as an electron-donating substituent on the aromatic rings and 3,5-difluorobenzyl groups as an electron-withdrawing substituent. 1H NMR and 19F{1H} NMR spectroscopy exhibited that the cyclen with the 4-methoxybenzyl groups formed a complex with Ag+ ions first, followed by the cyclen with the 3,5-difluorobenzyl groups. Next, we employed a compound (3MFM) with three cyclen units, where the cyclen at each end was functionalized with three 4-methoxybenzyl groups, and the central cyclen was functionalized with two 3,5-difluorobenzyl groups. Upon adding Ag+ ions, we observed that the cyclen units at both ends formed complexes with Ag+ ions initially, followed by the central cyclen forming a complex with Ag+ ions. When we used 4MFM, which is a V-shaped compound, the Ag+-induced-1H NMR chemical shift changes are almost the same results as the 3MFM. Furthermore, we synthesized a compound (3FMF) by interchanging the substituents on the cyclen units at the ends and the center. Interestingly, the order of the complex formation was reversed in this compound. These results demonstrated that tuning the electron density on the aromatic side arms through substituents makes it possible to achieve regioselective coordination with Ag+ ions in bis- or tris(tetra-armed cyclen)s.

Homo- and Heteromultinuclear Pseudocapsules Assembled from Calix[6]-mono-crown-5 and Alkali Metal Ions.

The formation of pseudocapsule type homo- and heteromultinuclear complexes of calix[6]-mono-crown-5 (H4L) encapsulating from 4 to 6 alkali metal ions is reported. H4L reacts with KOH to yield a hexanuclear potassium(I) complex [K6(HL)2(CH3OH)2]·CHCl3 (1) in which two bowl-shaped tripotassium(I) complex units are linked in a rim-to-rim fashion via the interligand C-H···π interactions. In the same reaction condition, RbOH afforded a tetranuclear rubidium(I) complex [Rb4(H2L)2(CH3OH)2(µ-H2O)2]·6CHCl3 (2). In 2, again two bowl-shaped dirubidium(I) complex units are held together by two bridging water molecules and C-H···π interactions that act as a glue to generate such an elegant pseudocapsule. Interestingly, a mixture of KOH and RbOH yielded a heterotetranuclear complex [K2Rb2(H2L)2(CH3OH)2(µ-H2O)2]·6CHCl3 (3). Similarly, two heterodinuclear bowl units [KRb(H2L)] in 3 are held together by two bridging water molecules and C-H···π interactions to form a heteromultinuclear pseudocapsule. In each heterodinuclear K+/Rb+ bowl unit of 3, Rb+ occupies the center of the crown loop while K+ locates inside the calix rim. Consequently, the proposed host discriminates not only on the types and numbers of the metal ions but also on their positional preferences in forming pseudocapsules. Solution studies by nuclear magnetic resonance and electrospray ionization-mass support the heterometallic (K+/Rb+) complexation by showing the superior binding affinity of Rb+ over K+ toward the crown loop. These results demonstrate how the metal-driven pseudocapsules are formed and present a new perspective on the metallosupramolecules of the calixcrown scaffold.

Unexpected Solvent-Dependent Self-Assembly of Alkali Metal Complexes of Calix[6]-mono-crown-4: Dinuclear Bowls, a Pseudo-Capsule, and a One-Dimensional Polymer.

1,4-Bridged calix[6]-mono-crown-4 (H4L) capable of metal binding was employed, and the influence of solvent variations on the formation of alkali metal complexes (1-6) was investigated. In the crystal, the bowl-shaped H4L host contains one water molecule in a good-fit fashion via H-bonds. When the H4L host was reacted with alkali metal hydroxides (M = Na, K, Rb, and Cs) in chloroform/methanol (solvent A), anion-free dinuclear bowl-shaped complexes of type [M2(H2L)] were isolated regardless of the metal ions. In the dinuclear bowl complexes 1-4, two metal ions (M1 and M2) show different binding behaviors: one (M1) locates inside the pocket like an "egg-in-nest", and the other (M2) positions above the M1 interacting with the calix rim. When chloroform/acetonitrile (solvent B) was used in potassium(I) complexation, interestingly, an elegant pseudo-capsule-type quadrunuclear complex 5 was isolated. In 5, two dipotassium(I) bowls in a rim-to-rim arrangement are triply bridged by one water and two acetonitrile molecules like a magic glue. However, in dichloromethane/methanol (solvent C), cesium(I) yielded an infinite product 6 in which dicesium(I) bowls are linked by cation-π interactions, giving rise to a one-dimensional zigzag coordination polymer. Taken collectively, all products share a dinuclear bowl unit, some of which are further extended to the pseudo-capsule or polymeric array, depending on the solvents. The results suggest the solvent variation as a versatile engineering tool and present a perspective on the metallosupramolecules of calix[6]-mono-crowns with monomer, dimer (e.g., pseudo-capsule), and polymer topologies.

Influence of the Reaction Sequence on the Complexation of an NS4-Macrocycle with CdII and CuI Salts Leading to the Formation of Supramolecular Isomers and an Endo/Exocyclic CuI Complex.

In the construction of metallosupramolecules, the reaction sequence in a three-reactant system (one ligand plus two metal ions) could be one of the controlling factors influencing the outcome of the reaction. In this work, the formation of supramolecular isomers (1 and 2) and an endo/exocyclic Cu+ complex (4) of the NS4-macrocycle (L) via different sequential metal addition protocols (routes I-III) is reported. In one-pot reactions of L with Cu(CH3CN)4PF6 in the absence (route I) and presence (route II) of CdI2, a cyclic dimer CuI complex, [Cu2(L)2](PF6)2 (1), and a one-dimensional coordination polymer, [Cu2(L)2]n·n[CdI4] (2), were obtained, respectively. Interestingly, the complex cations in 1 and 2 are supramolecular isomers formed via cyclization and polymerization upon complexation, respectively, probably due to different geometric and electronic complementarities, via the C-H···X- hydrogen bonds, between L and the counterion. In the two-step reaction (route III), an endocyclic Cd2+ complex, [Cd(L)I2] (3), obtained in the first step was utilized in the following reaction with Cu(CH3CN)4PF6, giving rise to an endo/exocyclic tetranuclear Cu+ complex, [Cu4(L)2(CH3CN)6](PF6)4 (4), via Cd2+ → 2Cu+ substitution, which is not accessible by conventional procedures. Solution studies by comparative NMR and electrospray ionization mass spectroscopy also support metal substitution by showing the stronger binding affinity of Cu+ over Cd2+. These results demonstrate that the metal substitution protocol could be useful for reaching novel metallosupramolecules difficult to obtain by other methods.

Synthesis, crystal structure and photophysical properties of chlorido-[2-(2',6'-di-fluoro-2,3'-bipyri-din-6-yl-κN 1)-6-(pyridin-2-yl-oxy-κN)phenyl-κC 1]platinum(II).

The title compound, [Pt(C21H12F2N3O)Cl], crystallizes with two crystallographically independent mol-ecules (A and B) in the asymmetric unit, which adopt similar conformations. The PtII atoms in both mol-ecules adopt distorted square-planar geometries, coordinated by one C and two N atoms from the tridentate 2',6'-di-fluoro-6-[3-(pyridin-2-yl-oxy)phen-yl]-2,3'-bi-pyridine ligand and a chloride anion: the C and Cl atoms are trans. In the crystal, C-H⋯Cl/F hydrogen bonds, F⋯π and weak π-π stacking inter-actions between adjacent A and B mol-ecules and between pairs of inversion-related B mol-ecules lead to the formation of a two-dimensional supra-molecular network lying parallel to the ab plane. The sheets are stacked along the c-axis direction and linked by F⋯π and weak π-π stacking inter-actions between pairs of inversion-related A mol-ecules, forming a three-dimensional supra-molecular network. The photoluminescence quantum efficiency of the title compound in the blue-green region of the visible region (λmax = 517 and 544 nm) is estimated to be ∼0.2-0.3, indicating that the title compound could be a suitable candidate as the emitting material in organic light-emitting diode (OLED) applications.

Pentacyclic Nano-Trefoil.

Tetra-armed cyclen (1) bearing two 4-(4'-pyridyl)benzyl and two 3,5-difluorobenzyl groups and its Ag+ complexes were prepared and structurally characterized. The complexes formed between 1 and Ag+ undergoes a reversible structural transformation between a 2:2 dimeric complex and a 3:5 pentacyclic trefoil complex with changes in the Ag+ /1 molar ratio. It was also revealed that the 3:5 trefoil complex could encapsulate benzene and [D6 ]benzene selectively in solid-state. The benzene-included structures are stabilized by C-H⋅⋅⋅F-C interactions between the benzene molecule and the ligand molecule.

Structures and photophysical properties of two luminescent bipyridine compounds: 2',6'-difluoro-6-[3-(pyridin-2-yloxy)phenyl]-2,3'-bipyridine and 2',6'-dimethoxy-6-[3-(pyridin-2-yloxy)phenyl]-2,3'-bipyridine.

The title compounds, C21H13F2N3O (1) and C23H19N3O3 (2), have been synthesized by typical cross-coupling reactions. Both compounds have been characterized by single-crystal X-ray diffraction. Bipyridine 1 exhibits a fully extended structure in which the terminal pyridine rings are oriented away from each other, while bipyridine 2 displays a bent structure in which terminal pyridine rings are oriented in the same direction. Several intermolecular interactions lead to the formation of two- and three-dimensional supramolecular networks in the crystal structures of 1 and 2, respectively. Compound 1 bears fluorine substituents and emits a strong fluorescence with λmax = 325 nm, while methoxy-substituted compound 2 displays red-shifted emissions with λmax = 366 nm. The emissions observed in both compounds originate from phenyl- and 2,3'-bipyridine-based π-π* transitions, according to theoretical calculations. Both compounds have high triplet energies (T1) ranging from 2.64 to 2.65 eV, which makes them potential host materials in organic light-emitting diodes (OLEDs).

Crystal structure and luminescence properties of 2-[(2',6'-dimeth-oxy-2,3'-bipyridin-6-yl)-oxy]-9-(pyridin-2-yl)-9H-carbazole.

In the title com-pound, C29H22N4O3, the carbazole system forms a dihedral angle of 68.45 (3)° with the mean plane of the bi-pyridine ring system. The bi-pyridine ring system, with two meth-oxy substituents, is approximately planar (r.m.s. deviation = 0.0670 Å), with a dihedral angle of 7.91 (13)° between the planes of the two pyridine rings. Intra-molecular C-H⋯O/N hydrogen bonds may promote the planarity of the bipyridyl ring system. In the pyridyl-substituted carbazole fragment, the pyridine ring is tilted by 56.65 (4)° with respect to the mean plane of the carbazole system (r.m.s. deviation = 0.0191 Å). In the crystal, adjacent mol-ecules are connected via C-H⋯O/N hydrogen bonds and C-H⋯π inter-actions, resulting in the formation of a three-dimensional (3D) supra-molecular network. In addition, the 3D structure contains inter-molecular π-π stacking inter-actions, with centroid-centroid distances of 3.5634 (12) Šbetween pyridine rings. The title com-pound exhibits a high energy gap (3.48 eV) and triplet energy (2.64 eV), indicating that it could be a suitable host material in organic light-emitting diode (OLED) applications.

Crystal structure and Hirshfeld surface analysis of 2,2''',6,6'''-tetra-meth-oxy-3,2':5',3'':6'',3'''-quaterpyridine.

In the title compound, C24H22N4O4, the four pyridine rings are tilted slightly with respect to each other. The dihedral angles between the inner and outer pyridine rings are 12.51 (8) and 9.67 (9)°, while that between inner pyridine rings is 20.10 (7)°. Within the mol-ecule, intra-molecular C-H⋯O and C-H⋯N contacts are observed. In the crystal, adjacent mol-ecules are linked by π-π stacking inter-actions between pyridine rings and weak C-H⋯π inter-actions between a methyl H atom and the centroid of a pyridine ring, forming a two-dimensional layer structure extending parallel to the ac plane. Hirshfeld surface analysis and two-dimensional fingerprint plots indicate that the most important contributions to the crystal packing are from H⋯H (52.9%) and H⋯C/C⋯H (17.3%) contacts.

Bipyridine-based iridium(iii) triplet emitters for organic light-emitting diodes (OLEDs): application and impact of phenyl substitution at the 5'-position of the N-coordinating pyridine ring.

Three blue phosphorescent homoleptic iridium(iii) complexes based on a bipyridine ligand were synthesized. The structures of these Ir(C^N)3 analogues were determined by single-crystal X-ray diffraction analysis. Two geometrical isomers, facial and meridional, formed as the major products, and the ratio of the products depended on the substituents. The photophysical and electrochemical properties of the complexes were analyzed, and they were used as dopants for the fabrication of phosphorescent organic light-emitting diodes (PHOLEDs). The dependence of current density on dopant concentration in the devices, as well as their external quantum efficiencies and current efficiencies, were evaluated. All complexes exhibited intense, sky-blue phosphorescent emission at λmax = 479, 484 and 488 nm, and the absolute quantum efficiencies in the thin films were high at 0.72, 0.75 and 0.81. A maximum current efficiency of 39.8 cd A-1 and an external quantum efficiency (EQE) of 14.9% were obtained, which signified superior performance among blue phosphorescent organic light-emitting diodes. High efficiencies of 39.2 cd A-1 and 14.0% EQE were still achieved at a luminance of 1000 cd m-2.

Crystal structure and Hirshfeld surface analysis of 1,2-bis-(2',6'-diisoprop-oxy-[2,3'-bipyridin]-6-yl)benzene.

The title mol-ecule, C38H42N4O4, displays a helical structure induced by the combination of the C-C-C-C torsion angle [-10.8 (2)°] between two 2,3'-bipyridyl units attached to the 1,2-positions of the central benzene ring and consecutive connections between five aromatic rings through the meta- and ortho-positions. Intra-molecular C-H⋯π inter-actions between an H atom of a pyridine ring and the centroid of a another pyridine ring contributes to the stabilization of the helical structure. In the crystal, weak C-H⋯π inter-actions link the title mol-ecules into a two-dimensional supra-molecular network extending parallel to the ac plane, in which the mol-ecules with right- and left-handed helical structures are alternately arranged. Hirshfeld surface analysis and two-dimensional fingerprint plots indicate that the mol-ecular packing is dominated by van der Waals inter-actions between neighbouring H atoms, as well as by C-H⋯π inter-actions. One isopropoxyl group is disordered over two sets of sites [occupancy ratio 0.715 (5):0.285 (5)].

Crystal structure and luminescent properties of bis-[2,6-dimethyl-3-(pyridin-2-yl-κN)pyridin-4-yl-κC4](2,2,6,6-tetra-methylhepta-ne-3,5-dionato-κ2O,O')iridium(III) ethyl acetate monosolvate.

In the solvated title compound, [Ir(C12H11N2)2(C11H19O2)]·CH3CO2C2H5, the IrIII ion adopts a distorted octa-hedral coordination environment resulting from its coordination by two C,N-chelating 2,6-dimethyl-3-(pyridin-2-yl)pyridin-4-yl ligands and one O,O'-chelating 2,2,6,6-tetra-methylhepta-ne-3,5-dionate ligand. The C,N-chelating ligands are perpendicular to each other [dihedral angle between the least-squares planes = 87.86 (5)°] and are arranged in a cis-C,C' and trans-N,N' fashion. In the crystal, pairwise C-H⋯π inter-actions between inversion-related IrIII complexes are present, forming a dimeric structure. The title complex shows bright bluish-green emission with good quantum efficiency in solution at room temperature.

Crystal structure of 2,3'-bi-pyridine-2',6'-dicarbo-nitrile.

The title compound, C12H6N4, crystallizes with four independent mol-ecules (A, B, C and D) in the asymmetric unit. The dihedral angles between the two pyridine rings in each mol-ecule are 25.25 (8)° in A, 5.51 (9)° in B, 11.11 (9)° in C and 16.24 (8)° in D. In the crystal, mol-ecules A and B are linked by C-H⋯N hydrogen bonds to form layers extending parallel to the ab plane, while mol-ecules C and D are linked by C-H⋯N hydrogen bonds forming -C-D-C-D- chains propagating along the b-axis direction. The layers and the chains are stacked alternately along the c axis through offset π-π and C≡N⋯π [N-to-pyridine-centroid distance = 3.882 (2) Å] inter-actions, resulting in the formation of a supra-molecular framework.

Crystal structure of an AgI inter-calation compound: catena-poly[[silver(I)-µ-N-(pyridin-3-ylmeth-yl)pyridin-3-amine-κ2N:N'] hexa-fluorido-phosphate aceto-nitrile disolvate].

The asymmetric unit in the title compound, [Ag(C11H11N3)]PF6·2CH3CN or {[AgL]·PF6·2CH3CN} n , L = N-(pyridin-3-ylmeth-yl)pyridin-3-amine, comprises one AgI atom, one L ligand, two aceto-nitrile solvent mol-ecules and one PF6- anion disordered over two orientations in a 0.567 (11):0.433 (11) ratio. Each AgI atom is coordinated by two pyridine N atoms from two L ligands in a slightly distorted linear coordination geometry [N-Ag-N = 170.55 (8)°]. Each L ligand bridges two AgI ions, resulting in the formation of a zigzag chain propagating along the [101] direction. In the crystal, Ag⋯Ag contacts [3.3023 (5) Å] and inter-molecular π-π stacking inter-actions [centroid-to-centroid distance = 3.5922 (15) Å] between the pyridine rings link these chains into a corrugated layer parallel to the ([Formula: see text]01) plane. The layers are stacked with a separation of 10.4532 (5) Å, and aceto-nitrile solvent mol-ecules and PF6- anions as guests are inter-calated between the layers. The layers are connected through several N/C-H⋯F hydrogen bonds and P-F⋯π inter-actions [F⋯ring centroid = 3.241 (8) Å] between the layer and the inter-calated guests and between the inter-calated guests, forming a three-dimensional supra-molecular network.

Crystal structure of a twisted-ribbon type double-stranded AgI coordination polymer: catena-poly[[silver(I)-µ3-bis-(pyridin-3-ylmeth-yl)sulfane-κ3N:N':S] nitrate].

The asymmetric unit in the title compound, {[Ag(C12H12N2S)]·NO3} n or {[AgL]·NO3} n , L = bis-(pyridin-3-ylmeth-yl)sulfane, consists of an AgI cation bound to a pyridine N atom of an L ligand and an NO3- anion that is disordered over two orientations in an 0.570 (17):0.430 (17) occupancy ratio. Each AgI cation is coordinated by two pyridine N atoms from adjacent L ligands to form an infinite zigzag chain along [110]. In addition, each AgI ion binds to an S donor from a third L ligand in an adjacent parallel chain, resulting in the formation of a twisted-ribbon type of double-stranded chain propagating along the [110] or [1-10] directions. The AgI atom is displaced out of the trigonal N2S coordination plane by 0.371 (3) Šbecause of inter-actions between the AgI cation and O atoms of the disordered nitrate anions. Inter-molecular π-π stacking inter-actions [centroid-to-centroid distance = 3.824 (3) Å] occur between one pair of corresponding pyridine rings in the double-stranded chain. In the crystal, the double-stranded chains are alternately stacked along the c axis with alternate stacks linked by inter-molecular π-π stacking inter-actions [centroid-to-centroid distance = 3.849 (3) Å], generating a three-dimensional supra-molecular architecture. Weak inter-molecular C-H⋯O hydrogen bonds between the polymer chains and the O atoms of the nitrate anions also occur.

A one-dimensional HgII coordination polymer based on bis-(pyridin-3-ylmeth-yl)sulfane.

The reaction of mercury(II) chloride with bis-(pyridin-3-ylmeth-yl)sulfane (L, C12H12N2S) in methanol afforded the title crystalline coordination polymer catena-poly[[di-chlorido-mercury(II)]-µ-bis-(pyridin-3-ylmeth-yl)sulfane-κ2N:N'], [HgCl2L] n . The asymmetric unit consists of one HgII cation, one L ligand and two chloride anions. Each HgII ion is coordinated by two pyridine N atoms from separate L ligands and two chloride anions. The metal adopts a highly distorted tetra-hedral geometry, with bond angles about the central atom in the range 97.69 (12)-153.86 (7)°. Each L ligand bridges two HgII ions, forming an infinite -(Hg-L) n - zigzag chain along the b axis, with an Hg⋯Hg separation of 10.3997 (8) Å. In the crystal, adjacent chains are connected by inter-molecular C-H⋯Cl hydrogen bonds, together with Hg-Cl⋯π inter-actions [chloride-to-centroid distance = 3.902 (3) Å], that form between a chloride anion and the one of the pyridine rings of L, generating a two-dimensional layer extending parallel to (101). These layers are further linked by inter-molecular C-H⋯π hydrogen bonds, forming a three-dimensional supra-molecular network.

Crystal structure of a zigzag CoII coordination polymer: catena-poly[[di-chlorido-bis-(methanol-κO)cobalt(II)]-µ-bis-(pyridin-3-ylmeth-yl)sulfane-κ2N:N'].

Reaction of bis-(pyridin-3-ylmeth-yl)sulfane (L) with cobalt(II) chloride in methanol led to the formation of the title coordination polymer, [CoCl2(C12H12N2S)(CH3OH)2] n , in which the CoII cation lies on a crystallographic inversion centre and the S atom of the L ligand lies on a twofold rotation axis. Each CoII ion is coordinated by two pyridine N atoms from two bridging L ligands, two O atoms from methanol mol-ecules and two chloride anions, all inversion-related. The complex unit has an elongated octa-hedral geometry, in which N2O2 donor atoms occupy the equatorial positions and two chloride anions occupy the axial positions. Each L ligand links two CoII ions, forming an infinite zigzag chain propagating along the c-axis direction and further stabilized by O-H⋯Cl hydrogen bonds between the methanol mol-ecules and the chloride anions. Adjacent chains in the structure are connected by inter-molecular C-H⋯Cl hydrogen bonds, resulting in the formation of a three-dimensional supra-molecular architecture.

Crystal structure of mer-tris-{2,6-di-fluoro-3-[5-(2-fluoro-phen-yl)pyridin-2-yl-κN]pyridin-4-yl-κC4}iridium(III) di-chloro-methane hemisolvate n-hexane hemisolvate.

The asymmetric unit of the title compound, [Ir(C17H11F2N2)3]·0.5CH3(CH2)4CH3·0.5CH2Cl2, comprises one IrIII atom, three 2,6-di-fluoro-3-[5-(2-fluoro-phen-yl)pyridin-2-yl]pyridin-4-yl ligands and half each of an n-hexane and a di-chloro-methane solvent mol-ecule located about crystallographic inversion centres. The IrIII atom displays a distorted octa-hedral coordination geometry, having three C,N-chelating 2,6-di-fluoro-3-[5-(2-fluoro-phen-yl)pyridin-2-yl]pyridin-4-yl ligands arranged in a meridional manner. The IrIII ion lies almost in the equatorial plane [deviation = 0.0069 (15) Å]. The average distance [2.041 (3) Å] of Ir-C bonds is slightly shorter than that [2.076 (3) Å] of Ir-N bonds. A variety of intra- and inter-molecular C-H⋯F and C-H⋯π hydrogen bonds, as well as inter-molecular C-F⋯π inter-actions, contribute to the stabilization of the mol-ecular and crystal structures, and result in the formation of a two-dimensional network parallel to the ab plane. No inter-actions between n-hexane solvent mol-ecules and the other components in the title compound are observed.

Crystal structure of a CoII coordination polymer with a dipyridyl ligand: catena-poly[[bis-(nitrato-κ2O,O')cobalt(II)]-µ-N-(pyridin-2-ylmeth-yl)pyridine-3-amine-κ3N,N':N''].

The asymmetric unit of the title compound, [Co(NO3)2L] n , L = N-(pyridine-2-ylmeth-yl)pyridine-3-amine (C11H11N3), contains one CoII centre, two nitrate anions and one L ligand in which the Cpy-C-N-Cpy moiety adopts a trans conformation with a torsion angle of -173.1 (3) Å. The coordination geometry of the CoII atom is a distorted penta-gonal bipyramid. One amine N atom from the L ligand and four O atoms from two η2-nitrato ligands form the basal plane and two pyridyl N atoms from two symmetry-related L ligands occupy the apical positions [N-Co-N = 171.86 (11)°]. The displacement of the central CoII atom from the basal plane (r.m.s. deviation = 0.085 Å) is 0.1491 (12) Å. Each bidentate nitrate group is bonded asymmetrically to the cobalt atom in an chelating fashion. The CoII ions are linked by the L ligands to form a zigzag chain propagating along the c-axis direction. Within the zigzag chain, C-H⋯O hydrogen bonds between the ligands and the nitrate anions are observed. Adjacent zigzag chains are connected via inter-molecular π-π stacking inter-actions [centroid-to-centroid distance = 3.844 (2) Å] between the pyridine rings together with N/C-H⋯O hydrogen bonds.

Crystal structure of a looped-chain CoII coordination polymer: catena-poly[[bis-(nitrato-κO)cobalt(II)]bis-[µ-bis-(pyridin-3-ylmeth-yl)sulfane-κ2N:N']].

The asymmetric unit of the title compound, [Co(NO3)2(C12H12N2S)2] n , contains a bis-(pyridin-3-ylmeth-yl)sulfane (L) ligand, an NO3- anion and half a CoII cation, which lies on an inversion centre. The CoII cation is six-coordinated, being bound to four pyridine N atoms from four symmetry-related L ligands. The remaining coordination sites are occupied by two O atoms from two symmetry-related nitrate anions in a monodentate manner. Thus, the CoII centre adopts a distorted octa-hedral geometry. Two symmetry-related L ligands are connected by two symmetry-related CoII cations, forming a 20-membered cyclic dimer, in which the CoII atoms are separated by 10.2922 (7) Å. The cyclic dimers are connected to each other by sharing CoII atoms, giving rise to the formation of an infinite looped chain propagating along the [101] direction. Inter-molecular C-H⋯π (H⋯ring centroid = 2.89 Å) inter-actions between one pair of corresponding L ligands and C-H⋯O hydrogen bonds between the L ligands and the nitrate anions occur in the looped chain. In the crystal, adjacent looped chains are connected by inter-molecular π-π stacking inter-actions [centroid-to-centroid distance = 3.8859 (14) Å] and C-H⋯π hydrogen bonds (H⋯ring centroid = 2.65 Å), leading to the formation of layers parallel to (101). These layers are further connected through C-H⋯O hydrogen bonds between the layers, resulting in the formation of a three-dimensional supra-molecular architecture.