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A 1:2:2:6 molar ratio of Cd(NO3)2 · 4H2O, Cu(NO3)2 · 3H2O, tris(2-aminoethylamine) (tren) and NH4NCS in aqueous solution at room temperature affords trinuclear complex of the type [Cu2Cd(tren)2(NCS)6] (1). The complex has been characterised using microanalytical, spectroscopic and magnetic results. X-ray diffraction measurements have been made to define the coordination sphere and long-range structure. 1 consists of two pentacoordinated copper(II) occupied by tren N atoms and one bridging SCN− N atom of the central trans-[Cd(NCS)4(SCN)2]4− molecular ion which bridges by the 1,3-thiocyanate. Each of these trinuclear units are engaged in intra as well as intermolecular N–H⋯S hydrogen bonding. Variable-temperature magnetic study shows no significant magnetic interactions among the metal ions.

MnCl2 · 4H2O, Cu(NO3)2 · 3H2O, tris(2-aminoethyl)amine (tren) and NH4NCS in a 1:4:4:10 molar ratio in aqueous solution results a bimetallic compound of the type [Cu(tren)(NCS)]4[Mn(NCS)6] (1) which has been characterized by microanalytical, physicochemical, spectroscopic and magnetic results. The structure of the complex is determined by X-ray diffraction study. Some pertinent crystal data are: monoclinic, space group P21/c, a = 11.0442(9) A, b = 14.4923(12) A, c = 19.2505(16) A, β = 91.95(10)°, and Z = 4. The crystal structure consists of a hydrogen bonded 3D network of [Cu(tren)(NCS)]+ and [Mn(NCS)6]4− ions. Manganese(II) has an MnN6 chromophore bound by six N atoms of the terminal thiocyanates. Each copper(II) centre is five coordinated by one N atom of terminal thiocyanate and four N atoms of the tripod ligand. Four copper(II) units are hydrogen bonded to form a hydrogen bonded tetramer. Each manganese(II) in turn is further engaged in hydrogen bonding to four such tetramers leading to the 3D network. Variable-temperature magnetic study shows no significant magnetic interactions among the metal ions connected by hydrogen bonding.

Treatment of Cd(NO3)2 · 4H2O with two equivalents of NH4NCS in combination with two equivalents of imH [imH=imidazole] or one equivalent of pfan [pfan=((pyridin-2-yl)formylidene)aniline] results neutral 1D polymers of the type [Cd(imH)2(NCS)(SCN)]n (1) or [Cd(pfan)(NCS)(SCN)]n (2). X-ray structure determinations show that in both polynuclear 1 and 2, octahedral CdII ions occupy centre of symmetry with a CdN4S2 chromophore. The metal ions are linked through N and S atoms of NCS− alternately in doubly bridged end-to-end fashion; two mutually trans N atoms of monodentate imH units complete hexacoordination of each metal centre in 1. Similar NCS-bibridging chain is present in 2 with one bidentate (N,N) Schiff base chelator (pfan) in cis orientation. The 1D chains in 1 are further engaged in intermolecular hydrogen bonding (N–H⋯S) between N of imH and coordinated S of NCS− along with aromatic π–π stacking of imH moieties that constrain the 1D chains to lie in bc-plane, which are further linked via C–H⋯π interactions. In 2, 1D chains participate in two kinds of π–π interactions. Supramers 1 and 2 display intraligand 1 ( π – π * ) fluorescence and intraligand 3 ( π – π * ) phosphorescence in glassy solutions (MeOH at 77 K).

The synthetic details, characterization data and single crystal X-ray structural analyses of [Zn(dpa)(N3)2] (1) and [Zn(dpa)(N3)(NO3)]2 (2) (dpa=2,2′-dipyridylamine) are described. Structural study reveals that the zinc(II) centre in 1 is in a pseudotetrahedral ZnN4 environment ligated by two terminal azide N atoms and two pyridine N atoms of the chelator. The coordination polyhedron around each metal ion in dinuclear 2 is best described as a ZnN4O2 distorted octahedron linked by two end-on azido bridges. The mononuclear units in 1 are engaged in bifurcated intermolecular hydrogen bonding (N–H…N) between amine N of dpa and coordinated N of azide along with aromatic π–π stacking leading to a 2D sheet. In 2, the dinuclear units participate in intermolecular N–H…O hydrogen bonding between amine N of dpa and bound O of bidentate nitrate in combination with π–π interactions resulting to a 3D supramolecular continuum. 1 and 2 display high energy intraligand 1(π–π*) fluorescence and intraligand 3(π–π*) phosphorescence in glassy solutions (DMF at 77 K). A band (372 nm) observed for both 1 and 2 in their solid-state emission spectra is an excimeric emission arising due to aromatic π–π interaction. The role of dpa, a tailored diimine (–N  C | –NH– C |  N–) in 1 and 2 is discussed towards functionalisation on crystal engineering and luminescence behaviour.

Pyrazine forms 1:1 complexes with cadmium(II) halides, CdX 2 · pyrazine (X = Cl, Br, I). The structures of all three members of this series have been determined by single-crystal X-ray diffraction. All of the complexes crystallize as infinite CdX 2 chains in which cadmium atoms are doubly bridged by pairs of halide atoms; pyrazine ligands complete the pseudo-octahedral coordination of the cadmium atoms and link the CdX 2 chains to form extended two-dimensional layers. While this type of coordination is fairly common for chloro and bromo derivatives, the iodo compound represents, to the best of our knowledge, the first example of an iodo derivative with this coordination. In each case the layers stack along the crystallographic a -axis to complete the structure. In the bromo and iodo complexes, which are isomorphous, the pyrazine ring planes are perpendicular to the plane of the layer. The chloro derivative has a very similar structure; however, the pyrazine rings are rotated by 19.3° away from perpendicular, bringing the ortho -CH groups into close proximity [2.89 (2) A] to a chloride atom.