Synthese, Struktur und EPR‐Untersuchungen von binuklearen Bis( N , N , N ‴, N ‴‐tetraisobutyl‐ N ′, N ″‐isophthaloylbis(thioureato))‐Komplexen des Cu II , Ni II , Zn II , Cd II und Pd II

Synthesis, Structure and EPR Investigations of binuclear Bis( N , N , N ‴, N ‴‐tetraisobutyl‐ N ′, N ″‐isophthaloylbis(thioureato)) Complexes of Cu II , Ni II , Zn II , Cd II and Pd II The synthesis of binuclear Cu II ‐, Ni II ‐, Zn II ‐, Cd II ‐ and Pd II ‐complexes of the quadridentate ligand N , N , N ‴, N ‴‐tetraisobutyl‐ N ′, N ″‐isophthaloylbis(thiourea) and the crystal structures of the Cu II ‐ and Ni II ‐complexes are reported. The Cu II ‐complex crystallizes in two polymorphic modifications: triclinic, $P{\bar 1}$ (Z = 1) and monoclinic, P 2 1 /c (Z = 2). The Ni II ‐complex was found to be isostructural with the triclinic modification of the copper complex. The also prepared Pd II ‐, Zn II ‐ and Cd II ‐complexes could not be characterized by X‐ray analysis. However, EPR studies of diamagnetically diluted Cu II /Pd II ‐ and Cu II /Zn II ‐powders show axially‐symmetric g and A Cu tensors suggesting a nearly planar co‐ordination within the binuclear host complexes. Diamagnetically diluted Cu II /Cd II powder samples could not be prepared. In the EPR spectra of the pure binuclear Cu II ‐complex exchange‐coupled Cu II ‐Cu II pairs were observed. According to the large Cu II ‐Cu II distance of about 7,50Å a small fine structure parameter D = 26·10 −4 cm −1 is observed; T‐dependent EPR measurements down to 5 K reveal small antiferromagnetic interactions for the Cu II ‐Cu II dimer. Besides of the dimer in the EPR spectra the signals of a mononuclear Cu II species are observed whose concentration is T‐dependent. This observation can be explained assuming an equilibrium between the binuclear Cu II ‐complex (Cu II ‐Cu II pairs) and oligomeric complexes with “isolated” Cu II ions.