The Synthesis and Crystal Structure of Bis(cyclo-l-histidyl-l-histidyl)copper(II) Perchlorate Tetrahydrate

Abstract

Abstract The title compound was prepared, and its structure then determined by X-ray structure analysis. The crystal is trigonal with the space group P3221, a=8.450(3), c=42.00(6)Å, and Z=3. The crystal structure has been determined from the diffractometer data and refined by a least-squares method to an R value of 0.103 for 1349 independent reflections with I>3σ(I). The cyclo-l-histidyl-l-histidyl is coordinated to the Cu atom via the N atoms of the respective imidazolyl groups. The coordination of Cu is not planar but distorted toward the tetrahedral configuration, the interplanar angle betweent (Remark: Graphics omitted.) planes being 29°. The complex has virtually D2 symmetry: there are two pseudo two-fold axes and one crystallographically imposed two-fold axis which relates two chelate rings. The chelate rings assume the δ conformation, and the ligating cyclo-l-histidyl-l-histidyl is of a folded form with a bowsprit-boat 2,5-piperazinedione ring. The electronic and circular dichroism spectra in the visible region are presented.