Structural Diversity in Ni Chain Coordination Polymers: Synthesis, Structures, Isomerism and Magnetism

Reaction of Ni(NCS)(2) with different co-ligands based on pyridine derivatives substituted in 4-position leads to the formation of 1D coordination polymers with the composition [Ni(NCS)(2)(co-ligand)(2)](n), in which the metal cations are coordinated octahedrally by two S- and two N-bonding thiocyanate anions as well as two neutral co-ligands and are linked into chains by mu-1,3-bridging thiocyanate anions. Dependent on the nature of the co-ligand, novel isomers with linear and corrugated chains are observed, in which the Ni cations are trans- or cis-cis-trans coordinated. This also includes a dimer and two isomeric chain compounds with 4-chloropyridine as ligand, of which one is metastable at room-temperature. For all these compounds, together with several additional Ni(NCS)(2) chain compounds, the values of the intrachain exchange interaction J are extracted based on magnetic measurements. The values of J for 13 different Ni(NCS)(2) compounds are compared with the structural results to investigate if there are some simple relations between the magnetic exchange, the metal coordination and the chain geometry. The low temperature magnetic properties of the Ni(NCS)(2) dimer and the chain compounds are also discussed based on magnetic and specific heat measurements.