Long-range exchange interaction in (2,2’-bipyridine-3,3’-dicarboxylic acid)dichlorocopper(II) monohydrate via lattice water: Single-crystal EPR studies

An examination of the crystal structure of the title complex revealed three pathways for magnetic exchange. Analysis of the bulk magnetic susceptibility data in the temperature range 5--303 K gave a value of J=-1.25 cm^-1 for the intradimer coupling. Single-crystal EPR spectra showed anomalous angular variation from which the molecular ssg tensor was derived using a decoupling procedure. The two intermolecular couplings [{}J'{}=0.0006(2) cm^-1 at 300 K and 0.0001(2) cm^-1 at 147 K, and J''{≥}0.056 cm^-1] involving multiatomic bridges were also derived from the EPR data. J'' involves equatorial-equatorial exchange between two coupled centers separated by 11.75 {} and is stronger than the axial-equatorial exchange between centers separated by 7.73 {}. The results were analyzed on the basis of a model that assumes participation of the uncoordinated lattice water in propagating exchange interaction through H bonds. Interpretation of the molecular ssg tensor resulted in an {}x²-y²〉 ground state with very little mixing of {}3z²-r²〉. The negligible electron density in the axial direction is responsible for the weak J'.