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

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 ($N3^-$) or chloroacetate(caa)} leads to a new cis-[Cr([14]-decane)($NCS)_2]ClO_4{\cdot}H_2O$ (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)($NCS)_2]ClO_4{\cdot}H_2O$ reveals that central chromium(III) has a distorted octahedral coordination environment and two $NCS^-$anions are bonded to the chromium(III) ion via the Ndonor atom in the cis positions. The angle $N_{axial}-Cr-N_{axial}$ deviates by 13$^{\circ}$ from the ideal value of 180$^{\circ}$ 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$^{\circ}$. The bond lengths of Cr-N between the chromium and $NCS^-$groups are 1.964(5) and 2.000(5) $\AA$. 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.