Syntheses and crystal structures of four metal–organic co-ordination networks constructed from cadmium(II) thiocyanate and nicotinic acid derivatives with hydrogen bonds

Four novel non-interpenetrating metal–organic co-ordination networks of the CdII–L–NCS− system have been prepared using potentially bridging nicotinic acid derivatives L [nicotinic acid (HL1), nicotinamide (L2), isonicotinamide (L3), or isonicotinate (L4)]. Their crystal structures were determined by X-ray diffraction. In [Cd(SCN)2(HL1)2]·HL11 each pair of cadmium(II) ions is bridged by two inversely related μ-NCS−-N,S ligands to form infinite chains with the remaining two trans positions of six-co-ordinated Cd atoms being occupied by two HL1 ligands, which form head-to-head double hydrogen bonds using the unco-ordinated carboxyl groups between adjacent chains to form two-dimensional layers. Weak S ⋯ S interactions between the NCS− ligands extend the layers into a three-dimensional framework with the channels enclosing HL1 guest molecules, which are interlinked into chains through O–H ⋯ N hydrogen bonds. [Cd(SCN)2(L2)2]·H2O 2 and [Cd(SCN)2(L3)2] 3 are interesting in that they contain unprecedented 16-membered [Cd4(μ-SCN-N,S)4] rings in the two-dimensional sheets. Between the sheets N–H ⋯ O amide–amide hydrogen bonds extend the two-dimensional layers to three-dimensional structures. [Cd(SCN)(L4)(H2O)] 4 exhibits two-dimensional wave-like networks with bridging NCS− and L4 ligands using both ends in co-ordination. The results demonstrate that the structures of the CdII–L–NCS system deeply depend on the nature of the nicotinic acid derivatives L.