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

Abstract

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–CH₂–CH₂–N(C₂H₅)₂ (L³), 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.