Influence of the Host Lattice upon the EPR Coupling Parameters of Copper-8-hydroxyquinolinate

Copper‐8‐hydroxyquinolinate was substituted into single crystals of phthalimide, phthalic acid, and 8‐hydroxyquinoline in order to study matrix effects on the magnetic properties of the metal complex. The substitution yielded highly ordered solid solutions. The doped purely organic single‐crystal matrices gave rise to well‐resolved EPR spectra allowing complete resolution of ⁶³Cu and ⁶⁵Cu and of the nitrogen hfs structure. The $g$ parameters and the copper and nitrogen hfs constants turned out to be sensitive to the surrounding host lattice. It is shown that the covalent bonding in $d^9$ systems can be influenced by the matrix and that planar paramagnetic complexes act as probes to study the crystal field of a matrix at certain sites of a lattice. Evidence is given that the position of the $g$ axes in the complex plane depends on the individual bonding conditions of a copper complex and is not a general property of all planar copper complexes with nearly orthorhombic symmetry.