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 Cd-II-L-NCS- system have been prepared using potentially bridging nicotinic acid derivatives L [nicotinic acid (HL1), nicotinamide (L-2), isonicotinamide (L-3), or isonicotinate (L-4)]. Their crystal structures were determined by X-ray diffraction. In [Cd(SCN)(2)(HL1)(2)]. HL1 1 each pair of cadmium(II) ions is bridged by two inversely related mu -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)(L-2)(2)].H2O 2 and [Cd(SCN)(2)(L-3)(2)] 3 are interesting in that they contain unprecedented 16-membered [Cd-4(mu -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)(L-4)(H2O)] 4 exhibits two-dimensional wave-like networks with bridging NCS- and L-4 ligands using both ends in co-ordination. The results demonstrate that the structures of the Cd-II-L-NCS system deeply depend on the nature of the nicotinic acid derivatives L.