Cr(III)-Tetraaza Macrocyclic Complexes Containing Auxiliary Ligands (Part III); Synthesis and Characterization of Cr(III)-Isothiocyanato, -Azido and -Chloroacetato Macrocyclic Complexes

Abstract

The reaction of cis-[Cr([14]-decane)(OH 2 ) 2 ] + ([14]-decane = rac-5,5,7,12,12,14-hexamethyl-1,4,8,11-teraazacyclotetradecane) with auxiliary ligands {L a = isothiocyanate (NCS - ), azide (N 3 - ) or chloroacetate(caa)} leads to a new cis-[Cr([14]-decane)(NCS) 2 ]ClO 4 .H 2 O (1), cis-[Cr([14]-decane)(N 3 ) 2 ]ClO 4 (2) or cis-[Cr([14]-decane)(caa) 2 ]ClO 4 (3). These complexes have been characterized by a combination of elemental analysis, conductivity, IR and Vis spectroscopy, mass spectrometry, and X-ray crystallography. Analysis of the crystal structure of cis-[Cr([14]-decane)(NCS) 2 ]ClO 4 .H 2 O reveals that central chromium(III) has a distorted octahedral coordination environment and two NCS anions are bonded to the chromium(III) ion via the N-donor atom in the cis positions. The angle N a x a l -Cr-N a x i a l deviates by 13° from the ideal value of 180 for a perfect octahedron. The bond angle N-Cr-N between the Cr(III) ion and the two nitrogen atoms of the isothiocyanate ligands is close to 90°. The bond lengths of Cr-N between the chromium and NCS - groups are 1.964(5) and 2.000(5) A. They are shorter than those between chromium and nitrogen atoms of the macrocycle. The IR spectra of 1, 2 and 3 display bands at 2073, 1344 and 1684 cm - 1 attributed to the NCS - , N 3 - and caa groups stretching vibrations, respectively.