Synthesis, structure and bonding of cadmium(II) thiocyanate systems featuring nitrogen based ligands of different denticity

Complexes catena-[di(4-amino-pyridine)di(μ-S,N-thiocyanato)cadmium(II)], _∞¹ [Cd(μ-SCN)₂(L¹) ₂] (1), catena-[{(1-pyridine-2-yl-ethylene)-hydrazine}di(μ-S,N- thiocyanato)cadmium(II)], _∞¹[Cd(μ-SCN) ₂(L²)] (2), and di-μ-S,N-thiocyanatobis{(N,N-diethyl- N′-(1-pyridine-2-yl-ethylidene)-ethane-1,2-diamine)(N-thiocyanato) cadmium(II)}, [Cd(NCS)(μ-SCN)(L³)]₂ (3) have been synthesized by reacting cadmium acetate/NH₄SCN with 4-amino-pyridine (L¹), C₅H₄N-C(CH₃)=NNH₂ (L²), and C₅H₄N-C(CH₃)=N-CH ₂-CH₂-N(C₂H₅)₂ (L ³), respectively, in methanol. Characterization by single-crystal X-ray crystallography shows that in compounds 1 and 2 the cadmium atoms have a 4N2S-hexa-coordination sphere, exhibiting pseudo-octahedral geometry. The cadmium atoms are bridged by two thiocyanate ions generating 1-D polymeric chains. Compound 3 is a centrosymmetric dimeric complex, with the cadmium atom pseudo octahedrally surrounded by a 5N1S coordination sphere. In compound 1 the crystal packing is controlled mainly by interchain N-H⋯N and C-H⋯π interactions between the aminopyridine moieties, whereas in complexes 2 and 3 π-stacking interactions between the pyridyl planes stabilize the interchain or intermolecular packing, respectively. Thiocyanate and pyridylimine chelation to metal center is also scrutinized with EHMO analysis.