Inferring unresolved hyperfine structure in liquid solution EPR:14N hyperfine structure in the 1∶1 copper-calcimycin complex

Abstract

Theoretical expressions for EPR line widths in liquids suggest the following two strategies for inferring unresolved hyperfine structure in near square planar copper(II) complexes and thereby identify the coordinating ligand atoms: (i) Increasing the resolution by reducing the line widths, by forming a mixed ligand complex of lower magnetic anisotropy. (ii) By demanding that the magnetic anisotropy determined from line widths, assuming unresolved hyperfine structure, should agree with that determined from frozen solution EPR spectrum.14N hyperfine structure from a coordinating cal (A N ∼ 12 G) in 1∶1 copper-calcimycin complex (Cu−cal) has been observed / inferred by the application of these strategies in 1∶1 chloroform-ethanol mixtures. It has been suggested that Cu−cal prepared in the presence of the bidentate ligand diethyldithiocarbamate (dtc−) is the mixed ligand complex Cu(dtc)(cal) in which cal is a bidentate ligand. The Cu−cal prepared in the presence of a monodentate anion AN (AN=NO 3 − , Br−, Cl− etc.) is Cu(AN)(cal) in which cal is a tridentate ligand. These complexes have near planar coordination geometry.