Structural characterisation and DFT studies of [Cr(cyclam)(O-dmso)Cl]2+:: a new precursor complex towards potential DNA intercalators

The synthesis and structural characterisation of the complex [Cr([14]aneN(4))(O-dmso)Cl](PF6)(2)(.)dmso is reported. The structural studies were carried out in gas-phase by electrospray mass spectrometry (ESMS) and in the solid state by single crystal X-ray diffraction. The metal complex shows a distorted octahedral coordination environment with the macrocycle adopting a folded cis-V conformation. The angle N-axial-Cr-N-axial deviates by only 12degrees from the ideal value of 180degrees for a perfect octahedron indicating that there is a good match between the size of the macrocyclic cavity and the size of Cr(III) ion. The ESMS shows that the complex loses a proton with concomitant opening of the [14]aneN(4) ring to give the [Cr([14]aneN(4)-H)(dmso)Cl](+) ion with a CH2=CH- pendant chain. This group interacts with dmso leading to the loss of this ligand and to the formation of the [Cr([14]aneN(4)-H)Cl](+) ion, which has the highest relative abundance (100%). DFT calculations reproduce the geometry of the paramagnetic complex and are consistent with its electronic spectrum. (C) 2003 Elsevier Science B.V. All rights reserved.