3-Cyanopyridine as a bridging and terminal ligand in coordination polymers

3-Cyanopyridine (3-CNpy) can act as a bridging or terminal ligand in transition metal coordination polymers. The compounds [(MBr2)-Br-II(3-CNpy)(4)] with M = Mn, Fe, Co, Ni (1a-4a) consist of individual complexes, in which the metal atom is octahedrally coordinated by two bromine atoms and four 3-cyanopyridine ligands, which coordinate through their pyridine N atoms only. Thermal decomposition at around 160 degrees C leads to the release of two 3-cyanopyridine molecules and the formation of [(MBr2)-Br-II(3-CNpy)(2)](n) with M = Mn, Fe, Co, Ni (1b-4b). For 3b and 4b two polymorphs were observed each (alpha-3b, beta-3b, alpha-4b, beta-4b). In all six phases the metal atoms are linked by bromine bridges into [(MBr2)-Br-II](n) chains. The 3-cyanopyridine ligands again act as terminal ligands coordinating with their pyridine N atoms. Upon further heating to around 250 degrees C, the compounds [(MBr2)-Br-II(3-CNpy)(1)](n) with M = Mn, Fe, Co, Ni (1c-4c) are obtained. 1c-4c are again built up from [(MBr2)-Br-II](n) chains with lateral 3-CNpy ligands, but additionally the cyano groups coordinate to the metal atoms. 1c-4c are the first compounds with 3-cyanopyridine as a bridging ligand between two 3d M2+ ions. The bridges connect neighbouring [(MBr2)-Br-II](n) chains and this results in the formation of a wavy, two-dimensional network. All crystal structures were determined from X-ray powder diffraction data.