Halide-bi-bridged polymers of amide substituted pyridines and -pyrazines: polymorphism, structures, thermal stability and magnetism

The crystal structures and magnetic properties of seven novel halide-bi-bridged polymers of Cu( ii ) and the related organic ligands isonicotinamide, nicotinamide and pyrazinamide were determined. Two concomitant, room temperature polymorphs were identified for each of the compounds di-μ 2 -chlorido-bis(isonicotinamide) copper( ii ) and di-μ 2 -bromido-bis(isonicotinamide) copper( ii ). One of the polymorphs of di-μ 2 -chlorido-bis(isonicotinamide) copper( ii ) displays a non-symmetric halide-bi-bridged portion that has never been reported before, the geometry of which significantly affects the magnetic exchange observed in this compound. In addition, the structures of di-μ 2 -chlorido-bis(nicotinamide) copper( ii ), di-μ 2 -chlorido-bis(pyrazinamide) copper( ii ) and di-μ 2 -bromido-bis(pyrazinamide) copper( ii ) are reported. The effect of the change in organic ligand on the resulting hydrogen bonding interactions, and packing of the polymers, as well as the magnetic isolation of the halide-bi-bridged chains is highlighted. Structures and magnetic properties are compared within the family of compounds, and with related compounds reported in the literature, and magneto-structural correlations are identified, while the thermal stability of the compounds is studied via thermogravimetric analysis. The structural trends, polymorphic behaviour, magnetic properties and thermal stability of a family of halide-bi-bridged polymers of CuX 2 and amide-substituted pyridines and -pyrazines are reported, and compared with related compounds in the literature.