Terminal Thiocyanate Research Articles

Tetra-kis(tri-ethyl-enediamin-1-ium) dodeca-μ2-chlorido-hexakis(thio-cyanato-κN)hexa-octa-hedro-niobate.

The crystal structure of the cluster complex salt, (C6H13N2)4[Nb6(NCS)6Cl12] or (H-DABCO)4[Nb6Cl12(NCS)6] (DABCO = tri-ethyl-enedi-amine or 1,4-di-aza-bicyclo-[2.2.2]octa-ne), comprises octa-hedral Nb6 cluster cores, which are μ2-coordinated by 12 chloride ligands (bridging the octa-hedral edges, inner ligand sphere). Furthermore, each Nb atom is N-bonded to a terminal thio-cyanate ligand (outer ligand sphere). The discrete clusters carry a charge of -4, which is compensated by four monoprotonated DABCO mol-ecules. These are arranged in rows, which are N-H⋯Cl and N-H⋯N hydrogen bonded to the anions and among each other.

Ancillary Ligand Coordination Directed Modes of Aggregation in Mixed-Valence Tetranuclear Cobalt Complexes: Synthesis, Structure, Field-Induced SIM Behavior, and Theoretical Insights

The contrasting metal–ion coordination reactivity behavior for the multisite ligand H3L ([2,6-bis-{(2-hydroxymethyl-phenylimino)methyl}-4-methylphenol]) with Co(ClO4)2·6H2O in the presence of ancillary ligands NaPiv (Piv = (CH3)3CCO2–) and NH4SCN afforded two different types of mixed-valence tetranuclear cobalt complexes, [CoIII3CoII(HL)(L)(μ4-O)(μ-OH)((CH3)3CCOO)2]ClO4·H2O (1) and [CoIII2CoII2(L)2(NCS)4(CH3CN)2]·CH3CN (2). In the first case, the presence of bridging pivalate anions triggered the oxido-hydroxido-bridged dual control for aggregation, whereas in the second case, terminal thiocyanate coordination forced the dicubane type of aggregation. The connectivity for different numbers of CoIII and CoII ions are achieved through contrasting bridges by ancillary water-molecule-derived HO– plus O2– linkers and ligand-anion-based double phenolato bridges, where terminal monodentate coordinations finally fulfill the octahedral geometries around the CoII ions. Alternating current/direct current (AC/DC) magnetic studies revealed field-induced slow magnetic relaxation for complex 1 that arises from the single octahedral CoII ion connected to three other diamagnetic CoIII ions. Whereas in complex 2, having a tetranuclear CoIII2CoII2 structure, the two CoII centers showed an antiferromagnetic interaction (J = −0.39 cm–1). The structural distortions in these two types of aggregates lead to different magnitudes of easy-axis magnetic anisotropy (D = −51.31 cm–1 for 1 and −31.9 cm–1 for 2) and a small but non-negligible transverse component (E/D = 0.263 for 1 and 0.255 for 2). The static and dynamic magnetic data were analyzed using DFT and CASSCF-based calculations.

Three new zinc(II) 4′-chloro-2,2′:6′,2ʺ-terpyridine (4′-Cltpy)-based complexes: synthesis, spectroscopic and structural studies, thermal behavior, and Hirshfeld surface analysis

Three new ZnII complexes with the ligand 4′-chloro-2,2′:6′,2ʺ-terpyridine (4′-Cltpy), [Zn(4′-Cltpy)(N3)2] (1), [Zn(4′-Cltpy)(NCS)2] (2) (two 1:1 metal/ligand complexes) and a 1:2 metal/ligand complex, [Zn(4′-Cltpy)2](NO3)2·2H2O (3), have been synthesized and characterized by elemental analysis, IR, 1H NMR spectroscopy and single-crystal X-ray diffraction. The structures of 1 and 2 contain a ZnN5 coordination sphere, which includes coordination from three nitrogen donors of the 4′-Cltpy ligand and two nitrogen atoms of two terminal azide or two terminal thiocyanate ligands, respectively. Addison’s τ value suggests a distorted square pyramidal coordination of ZnII in 1 and intermediate between square pyramidal and trigonal bipyramidal in 2. In the complex cation of 3, the ZnII center is coordinated by six nitrogen atoms from two 4′-Cltpy ligands in a distorted octahedral coordination geometry. In this structure, two non-coordinating nitrate anions serve as counterions, and there are two non-coordinating solvent water molecules. Hirshfeld surface analysis was employed to clarify the nature and extent of intermolecular interactions. In addition, the thermal stabilities of the compounds were evaluated by thermogravimetric analysis (TGA).

Potential Anticancer Activities and Catalytic Oxidation Efficiency of Platinum(IV) Complex.

The treatment of an aqueous acetonitrile solution of chloroplatinic acid hydrate H2PtCl6.xH2O and pyridine-2-carbaldehyde-oxime (paOH) in the presence of potassium thiocyanate at room temperature (25°) led to the formation of a new Pt(IV) complex with the formula [Pt(SCN)2(paO)2], (1). Complex 1 was fully characterized by FT-IR, UV-vis and NMR spectroscopic techniques as well as elemental analysis. The crystallographic structure of complex 1 was obtained by single-crystal X-ray diffraction. The structure of complex 1 consists of a distorted octahedral geometrical environment around the platinum center in which the coordination sites are occupied by two terminal thiocyanate ligands in trans arrangement and two bidentate paO ligands through four nitrogen atoms. In addition, the in vitro evaluation of the cytotoxicity of platinum complex 1 against four different cancer cell lines was performed. The IC50 values for colon (HCT116), liver (HepG2), breast (MCF-7) and erythroid (JK-1) treated with complex 1 are 19 ± 6, 21 ± 5, 22 ± 6, and 13 ± 3 μM, respectively. In HCT116 cells treated with the IC50 dose of our title compound, apoptosis and necrosis were increased by 34% and 27.8%, respectively. Cells halted in the proliferative phase (S phase) to 21.7 % and 29.8% in HCT116 and HepG2 cells treated with complex 1 have anti-proliferative actions. Furthermore, the catalytic activity of synthesized complex 1 was examined in the oxidation reaction of benzyl alcohols in the presence of an oxidant. Finally, the luminescence behavior of complex 1 was investigated.

Synthesis, crystal structure and thermal properties of bis-(1,3-di-cyclo-hexyl-thio-urea-κS)bis(iso-thiocyanato-κN)cobalt(II).

Crystals of the title compound, [Co(NCS)2(C13H24N2S)2], were obtained by the reaction of Co(NCS)2 with 1,3-di-cyclo-hexyl-thio-urea in ethanol. Its crystal structure consists of discrete complexes that are located on twofold rotation axes, in which the CoII cations are tetra-hedrally coordinated by two terminal N-bonded thio-cyanate anions and two 1,3-di-cyclo-hexyl-thio-urea ligands. These complexes are linked via inter-molecular N-H⋯S and C-H⋯S hydrogen bonding into chains, which elongate in the b-axis direction. These chains are closely packed in a pseudo-hexa-gonal manner. The CN stretching vibration of the thio-cyanate anions located at 2038 cm-1 is in agreement with only terminal bonded anionic ligands linked to metal cations in a tetra-hedral coordination. TG-DTA measurements prove the decomposition of the compound at about 227°C. DSC measurements reveal a small endothermic signal before decomposition at about 174°C, which might correspond to melting.

Crystal structure of di-ethano-lbis(thio-cyanato)-bis(urotropine)cobalt(II) and tetra-ethano-lbis(thio-cyanato)-cobalt(II)-urotropine (1/2).

The reaction of one equivalent Co(NCS)2 with four equivalents of urotropine (hexa-methyl-ene-tetra-mine) in ethanol leads to the formation of two compounds, namely, bis-(ethanol-κO)bis-(thio-cyanato-κN)bis-(urotropine-κN)cobalt(II), [Co(NCS)2(C6H12N4)2(C2H6O)2] (1), and tetra-kis-(ethanol-κO)bis-(thio-cyanato-κN)cobalt(II)-urotropine (1/2), [Co(NCS)2(C2H6O)4]·2C6H12N4 (2). In 1, the Co cations are located on centers of inversion and are sixfold coordinated by two terminal N-bonded thio-cyanate anions, two ethanol and two urotropine ligands whereas in 2 the cobalt cations occupy position Wyckoff position c and are sixfold coordinated by two anionic ligands and four ethanol ligands. Compound 2 contains two additional urotropine solvate mol-ecules per formula unit, which are hydrogen bonded to the complexes. In both compounds, the building blocks are connected via inter-molecular O-H⋯N (1 and 2) and C-H⋯S (1) hydrogen bonding to form three-dimensional networks.

Synthesis, crystal structure and thermal properties of poly[bis-[μ2-3-(amino-meth-yl)pyridine]-bis-(thio-cyanato)-cobalt(II)

The reaction of Co(NCS)2 with 3-(amino-meth-yl)pyridine as coligand leads to the formation of crystals of the title compound, [Co(NCS)2(C6H8N2)2] n , that were characterized by single-crystal X-ray analysis. In the crystal structure, the CoII cations are octa-hedrally coordinated by two terminal N-bonded thio-cyanate anions as well as two pyridine and two amino N atoms of four symmetry-equivalent 3-(amino-meth-yl)pyridine coligands with all pairs of equivalent atoms in a trans position. The CoII cations are linked by the 3-(amino-meth-yl)pyridine coligands into layers parallel to the ac plane. These layers are further linked by inter-molecular N-H⋯S hydrogen bonding into a three-dimensional network. The purity of the title compound was determined by X-ray powder diffraction and its thermal behavior was investigated by differential scanning calorimetry and thermogravimetry.

Combined experimental and computational approach to the structure of a new nickel(II) complex with tridentate Schiff base ligand

A combined experimental and theoretical study on a new complex [NiL(NCS)], derived from the Schiff base ligand HL, (E)-2-methoxy-6-(((pyridin-2-ylmethyl)imino)methyl)phenol is described herein. X-ray structure reveals that metal center of the complex has a square planar environment with a N3O donor set from the ligand and terminal thiocyanate anion. In the solid state, π—π stacking interactions lead to a one-dimensional arrangement with alternating short and long Ni…Ni distances. The different isomeric forms of the ligand can provide alternative molecular structures for the nickel(II) complex. Density functional theory calculations at B3LYP/6-311+G(d,p) level were performed to elucidate the structure and stability of the possible isomeric forms of the complex.

Crystal and mol-ecular structures of a binuclear mixed ligand complex of silver(I) with thio-cyanate and 1H-1,2,4-triazole-5(4H)-thione.

The complete mol-ecule of the binuclear title complex, bis-[μ-1H-1,2,4-triazole-5(4H)-thione-κ2 S:S]bis-{(thio-cyanato-κS)[1H-1,2,4-triazole-5(4H)-thione-κS]silver(I)}, [Ag2(SCN)2(C2H3N3S)4], is generated by crystallographic inversion symmetry. The independent triazole-3-thione ligands employ the exocyclic-S atoms exclusively in coordination. One acts as a terminal S-ligand and the other in a bidentate (μ2) bridging mode to provide a link between two AgI centres. Each AgI atom is also coordinated by a terminal S-bound thio-cyanate ligand, resulting in a distorted AgS4 tetra-hedral coordination geometry. An intra-molecular N-H⋯S(thio-cyanate) hydrogen bond is noted. In the crystal, amine-N-H⋯S(thione), N-H⋯N(triazol-yl) and N-H⋯N(thio-cyanate) hydrogen bonds give rise to a three-dimensional architecture. The packing is consolidated by triazolyl-C-H⋯S(thio-cyanate), triazolyl-C-H⋯N(thiocyanate) and S⋯S [3.2463 (9) Å] inter-actions as well as face-to-face π-π stacking between the independent triazolyl rings [inter-centroid separation = 3.4444 (15) Å]. An analysis of the calculated Hirshfeld surfaces shows the three major contributors are due to N⋯H/H⋯N, S⋯H/H⋯S and C⋯H/H⋯C contacts, at 35.8, 19.4 and 12.7%, respectively; H⋯H contacts contribute only 7.6% to the overall surface.

Synthesis and characterisation of isothiocyanate functionalised silicon nanoparticles and their uptake in cultured colonic cells.

The functionalisation of silicon nanoparticles with a terminal thiocyanate group, producing isothiocyanate-capped silicon nanoparticles (ITC-capped SiNPs) has been successfully attained. The procedure for the synthesis is a two-step process that occurs via thermally induced hydrosilylation of hydrogen terminated silicon nanoparticles (H-SiNPs) and further reaction with potassium thiocyanate (KSCN). The synthesis was confirmed by Fourier transform infrared (FTIR) spectroscopy and X-Ray photoelectron spectroscopy (XPS). At the same time, the internalisation and the cytotoxicity of the ITC-capped SiNPs in vitro were assessed in two cell lines: Caco-2, human colorectal cancer cells and CCD-841, human colon "normal" cells. The results showed that above concentrations of 15 µg ml-1, the cell viability of both cell lines was depleted significantly when treated with ITC SiNPs, particularly over a 48 hour period, to approximately 20% cell viability at the highest treatment concentration (70 µg ml-1). Flow cytometry was employed to determine cellular uptake in Caco-2 cells treated with ITC SiNPs. It was observed that at lower SiNP concentrations, uptake efficiency was significantly improved for time periods under 12 hours; overall it was noted that cellular uptake was positively dependent on the period of incubation and the temperature of incubation. As such, it was concluded that the mechanism of uptake of ITC SiNPs was through endocytosis. Synchrotron FTIR spectroscopy, by means of line spectral analysis and IR imaging, provided further evidence to suggest the internalisation of ITC SiNPs displays a strong localisation, with an affinity for the nucleus of treated Caco-2 cells.

A series of 1-D zinc(II) coordination polymers with 3-D supramolecular networks: synthesis, structural investigation, and NBO analysis

N,N′-Bis(pyridin-4-ylmethylene)naphthalene-1,5-diamine (L) acts as a bipyridine analogue linker ligand towards {Zn7(μ4-O)2(OAc)10}, {Zn2(NCS)2(OAc)2}, and {Zn(N3)2} nodes and allows construction of three new 1-D coordination polymers, the linear chain [Zn7(μ4-O)2(OAc)10(L)]n (1), [Zn(NCS)(OAc)(L)]n (2) in ladder-type geometry and the zigzag chain [Zn(N3)2(L)]n (3). Structural characterization reveals that in 1 acetate anionic ligands connect seven Zn(II) ions through the bridging coordination modes μ3-η1,η2 and μ2-η1,η1. The resulting heptanuclear node is located on an inversion center and therefore consists of four crystallographically distinct cations; their coordination spheres correspond to distorted octahedra or tetrahedra. The Zn(II) ions in polymer 2 exhibit distorted trigonal bipyramidal {ZnN3O2} coordination; μ2-η1,η1 coordinated acetate and terminal thiocyanate ligands lead to inversion-symmetric [Zn2(NCS)2(OAc)2] secondary building units (SBU), which are further linked by the N,N′-bipyridine analogue L. Terminal coordination of two anionic azide ligands and the bridging bipyridine L result in coordination polymer 3, in which the cations adopt distorted tetrahedral {ZnN4} coordination. In all crystalline solids 1–3, adjacent 1-D chains interact through π–π stacking and non-classical (C − H···O, C − H···π) hydrogen bonds, leading to 3-D supramolecular architectures. Differences in their 3-D arrangement are due to variations in the anionic co-ligands, subtle conformational differences in the semi-rigid linker and the variable coordination sphere about the zinc cations. Thermogravimetric investigations indicate differences in both thermal stability and decomposition mode. Natural bond orbital (NBO) analysis provides a convenient basis for investigating the intramolecular bonding interactions and delocalization effects in these molecular systems. Finally, solids 1–3 exhibit intense luminescence at room temperature.

Syntheses, crystal structures and luminescence behaviors of four neutral penta-/hexacoordinate cadmium(II) compounds containing a tridentate Schiff base: Variation in coordination numbers, nuclearities and dimensionalities by changing halides/pseudohalides

Two neutral pentacoordinate mononuclear cadmium(II) complexes of the type [Cd(L)X2] [L = N-(pyridin-2′-yl)benzylidene)-2-(piperidin-1-yl)ethane-1,2-diamine; X = Cl, (1) and X = Br, (2)], one neutral hexacoordinate dinuclear compound [Cd(L)(µ-NCS)NCS]2 (3) and one neutral hexacoordinate coordination polymer [Cd(L)(µ-N3)N3]n (4) have been prepared and characterized using microanalytical, spectroscopic, thermal and X-ray crystallographic results. Structural analyses show that each cadmium(II) center in the isostructural compounds 1 and 2 adopts a distorted square pyramidal geometry with a CdN3X2 [X = Cl in 1 and X = Br in 2] chromophore through coordination of three N atoms of L and two terminal halides. In 3 and 4, each metal(II) center affords a distorted octahedral geometry with MN5S (in 3) and MN6 (in 4) chromophores. Each metal(II) center in dinuclear compound 3 is attached to three N-atoms of L, one N-atom of terminal thiocyanate, and one N-atom and one S-atom of two μ1,3-bridging thiocyanate units, whereas three N-atoms of L and three N-atoms of one terminal and two μ1,3-bridging azide units are bound to each metal(II) center in the coordination polymer 4. Each metal(II) center in 4 is connected to two other metal(II) centers through two different μ1,3-azide bridges affording a zigzag one-dimensional (1D) chain. In the crystalline state, mononuclear units in both 1 and 2 are stabilized through intermolecular CH∙∙∙X (X = Cl in 1 and X = Br in 2) hydrogen bonds promoting to 2D sheet structures. The dinuclear units in 3 pack through cooperative intermolecular CH∙∙∙S and CH∙∙∙N hydrogen bonds giving rise to a 3D network structure. 1D chains in 4 are stabilized through cooperative intermolecular CH∙∙∙N hydrogen bonds promoting to a 2D sheet structure. These 2D sheets, in turn, self-assemble through weak non-covalent π∙∙∙π interactions to afford a 3D network structure. The thermally stable compounds (1–4) exhibit intraligand 1(π-π∗) fluorescence in DMF solutions at room temperature with lifetimes in range 0.83–2.94 ns.

A Template-Directed Approach for the Synthesis of a New Mono-Condensed Schiff Base Complex of Copper(II)

In this paper, the formation of Schiff base compounds has been explained by the templating effect of a metal ion modulated by counter anions. It is shown that a dicondensed Schiff ligand can utilize the N2O2 compartment to form a stable copper complex. However, in the presence of a strongly coordinating thiocyanate ion, the dicondensed ligand is converted to the corresponding monocondensed ligand to yield a square planar copper(II) complex coordinated by the NNO donor set of the Schiff base and the terminal thiocyanate coligand. This template approach provides a methodology to trap the monocondensed ligand HL2 [2-((E)-(3-aminopropylimino)methyl)-6-methoxyphenol] as its Cu(II) compound [CuL2(NCS)]. We report herein the crystal structure and spectroscopic studies of this newly synthesized complex.

Crystal structures of tetra-kis-(pyridine-4-thio-amide-κN)bis-(thio-cyanato-κN)cobalt(II) monohydrate and bis-(pyridine-4-thio-amide-κN)bis-(thio-cyanato-κN)zinc(II).

Reaction of Co(NCS)2 and Zn(NCS)2 with 4-pyridine-thio-amide led to the formation of compounds with composition [Co(NCS)2(C6H6N2S)4]·H2O (1) and [Zn(NCS)2(C6H6N2S)2] (2), respectively. The asymmetric unit of compound 1, consists of one cobalt(II) cation, two thio-cyanate anions, four 4-pyridine-thio-amide ligands and one water mol-ecule whereas that of compound 2 comprises one zinc(II) cation that is located on a twofold rotation axis as well as one thio-cyanate anion and one 4-pyridine-thio-amide ligand in general positions. In the structure of compound 1, the cobalt(II) cations are octa-hedrally coordinated by two terminal N-bonding thio-cyanate anions and by the N atoms of four 4-pyridine-thio-amide ligands, resulting in discrete and slightly distorted octa-hedral complexes. These complexes are linked into a three-dimensional network via inter-molecular N-H⋯S hydrogen bonding between the amino H atoms and the thio-cyanate S atoms. From this arrangement, channels are formed in which the water mol-ecules are embedded and linked to the host structure by inter-molecular O-H⋯S and N-H⋯O hydrogen bonding. In the structure of compound 2, the zinc(II) cations are tetra-hedrally coordinated by two N-bonding thio-cyanate anions and the N atoms of two 4-pyridine-thio-amide ligands into discrete complexes. These complexes are likewise connected into a three-dimensional network by inter-molecular N-H⋯S hydrogen bonding between the amino H atoms and the thio-amide S atoms.

Crystal structure of bis-(pyridine-4-carbo-thio-amide-κN1)bis-(thio-cyanato-κN)cobalt(II) methanol monosolvate.

The asymmetric unit of the title compound, [Co(NCS)2(C6H6NS)4]·CH3OH, consists of one cobalt(II) cation, two thio-cyanate anions, four pyridine-4-carbo-thio-amide ligands and one methanol mol-ecule that are located in general positions. The CoII cations are coordinated by two terminal N-bonding thio-cyanate anions and four N-bonding pyridine-4-carbo-thio-amide ligands, resulting in discrete and slightly distorted octa-hedral complexes. These complexes are linked into a three-dimensional network via inter-molecular N-H⋯S hydrogen bonding between the amino H atoms and the thio-cyanate and pyridine-4-carbo-thio-amide S atoms. From this arrangement, channels are formed in which the methanol solvate mol-ecules are embedded and linked to the host structure by inter-molecular O-H⋯S and N-H⋯O hydrogen bonding.

(Thiocyanato-κS)tris(triphenylphosphane-κP)silver(I)

In the mononuclear title complex, [Ag(SCN)(C18H15P)3], the AgIcenter is in a slightly distorted tetrahedral coordination geometry formed by one S atom from a terminal thiocyanate ligand and three P atoms from three triphenylphosphane ligands. In the crystal, weak C—H...N hydrogen bonds connect molecules into a two-dimensional network parallel to (10\overline{1}). One of the phenyl rings is disordered over two positions which were refined with an occupancy ratio of 0.715 (16):0.285 (16).

Crystal structure of bis-(aceto-nitrile-κN)bis-(4-benzoyl-pyridine-κN)bis-(thio-cyanato-κN)cobalt(II).

The crystal structure of the title compound, [Co(NCS)2(C2H3N)2(C12H9NO)2], consists of cobalt(II) cations that are octa-hedrally coordinated by the N atoms of two terminal thio-cyanate anions, two aceto-nitrile mol-ecules and two 4-benzoyl-pyridine ligands. The discrete complexes are located on centres of inversion. They are connected by weak inter-molecular C-H⋯O and C-H⋯S hydrogen-bonding inter-actions between one of the pyridine H atoms and the carbonyl O atom, and between one of the methyl H atoms of the aceto-nitrile mol-ecule and the thio-cyanate S atoms into layers parallel to (101). No pronounced inter-molecular inter-actions are observed between these layers.

Spectroscopic and DFT studies of zinc(II) complexes of diamines and thiocyanate; crystal structure of (cis-1,2-diaminocyclohexane)bis(thiocyanato-κN)zinc(II)

Zinc(II) complexes of diamines, cis-1,2-diaminocyclohexane (Dach) and N,N,N,N-tetramethylethylenediamine (Tmen), [Zn(Dach)(NCS)2] (1) and [Zn(Tmen)(NCS)2] (2) have been prepared and characterized by elemental analysis, IR, 1H &13C NMR spectroscopy. The crystal structure of [Zn(Dach)(NCS)2] (1) was determined by X-ray crystallography. In 1, the Zn(II) atom is bound to one 1,2-diaminocyclohexane molecule and to two terminal thiocyanate ions via the nitrogen atoms adopting a slightly distorted tetrahedral geometry. In the crystal structure, molecules are linked through intermolecular NH⋯S hydrogen bonds, forming chains running along the a axis. The structures of 1 and 2 as well as of [Zn(En)(NCS)2] (3) (En = 1,2-diaminoethane) were predicted using theoretical (DFT) method. The interaction energies (ΔE) for NCS anions obtained by B3LYP-D3 method are about −140 kcal mol−1, while the calculated ΔE values for neutral organic ligands are about twice smaller. The atomic charges and second-order interaction energies between orbitals were calculated with natural bond orbital (NBO) analysis.

The ligating versatility of pseudohalides like thiocyanate and cyanate in copper(II) complexes of 2-benzoylpyridine semicarbazone: Monomer, dimer and polymer

Three new copper(II) complexes [Cu(bpsc)(NCS)]n (1), [Cu(Hbpsc)(NCS)2] (2) and [Cu(bpsc)μ2(NCO)]2 (3) of a semicarbazone Hbpsc (where Hbpsc=2-benzoylpyridine semicarbazone) with pseudohalides like thiocyanate and cyanate have been synthesized and characterized by elemental analyses, magnetic susceptibility and conductivity measurements, FT-IR, UV–Vis and EPR spectral studies. The interesting amido-iminol tautomerism enables the proligand to exist in amido form as well as deprotonated iminolate form thereby functioning as tridentate NNO donor, coordinating through pyridyl nitrogen atom, azomethine nitrogen atom and amido/iminolate oxygen atom in the complexes. Versatile coordinating behavior of pseudohalides gives rise to complexes with different nuclearities. Single crystal XRD studies showed that [Cu(bpsc)(NCS)]n (1) is a one dimensional polymer connected by single end-to-end (μ1,3) thiocyanate bridges whereas [Cu(Hbpsc)(NCS)2] (2) is monomeric in nature in which copper(II) center is bonded to two terminal thiocyanate groups. [Cu(bpsc)μ2(NCO)]2 (3) is an end-on cyanato bridged binuclear species and found to exhibit packing polymorphism. In all complexes, g values in frozen DMF indicate the presence of the unpaired electron residing in the dx2-y2 orbital.

Crystal structure of di-aqua-bis-(2,6-di-methyl-pyrazine-κN (4))bis-(thio-cyanato-κN)cobalt(II) 2,5-di-methyl-pyrazine monosolvate.

In the crystal structure of the title compound, [Co(NCS)2(C6H8N2)2(H2O)2]·C6H8N2, the CoII cation is coordinated by the N atoms of two terminal thio­cyanate anions, the O atoms of two water mol­ecules and two N atoms of two 2,6-di­methyl­pyrazine ligands. The coordination sphere of the resulting discrete complex is that of a slightly distorted octa­hedron. The asymmetric unit comprises a CoII cation and half of a 2,5-di­methyl­pyrazine ligand, both of which are located on centres of inversion, and a water ligand, a 2,6-di­­methyl­pyrazine ligand and one thio­cyanate anion in general positions. In the crystal, the discrete complexes are arranged in such a way that cavities are formed in which the 2,5-di­methyl­pyrazine solvent mol­ecules are located. The coordination of the 2,5-di­methyl­pyrazine mol­ecules to the metal is apparently hindered due to the bulky methyl groups in vicinal positions to the N atoms, leading to a preferential coordination of the 2,6-di­methyl­pyrazine ligands. The discrete complexes are linked by O—H⋯N hydrogen bonds between one water H atom and the non-coordinating N atom of the 2,6-di­methyl­pyrazine ligands. The remaining water H atom is hydrogen bonded to one N atom of the 2,5-di­methyl­pyrazine solvent mol­ecule. This arrangement leads to the formation of a two-dimensional network extending parallel to (010).