Two new canted antiferromagnetic systems: magnetic, theoretical, and crystallographic studies on trans-bis(2-iodopyridine)dihalocopper(ii)

Abstract

The two complexes Cu(2ip)X₂ were prepared (where 2ip = 2-iodopyridine and X = Cl or Br), and their crystal structures were determined. The two complexes are isomorphous and form a magnetic chain based on the two-halide exchange pathway. The powder and single crystal magnetic susceptibility data were measured down to 1.8 K. The exchange is antiferromagnetic along the chain; the exchange is stronger in the bromide complex than in the corresponding chloride complex. In the ordered state, weak moments appear along some of the axes, indicative of spin-canting. The calculated spin densities and the mapped surface of spin density on total electron density were used to rationalize qualitatively the observed magnetic behavior. Low temperature structures are compared with the room temperature data; the C–I⋯X–Cu and Cu–X⋯X–Cu distances are shorter at low temperatures; in contrast, the covalent bonds of the organic ligand (2-iodopyridine) are longer (negative thermal expansion of the covalent bonds). The anomalous behavior is rationalized using charge transfer from Cu–X group to the anti-bonding orbital of the organic ligand. Quantum theory of atoms in molecules was used to analyze C–I⋯X halogen bonding interactions.