ELECTRON-SPIN-RESONANCE STUDIES AND CRYSTAL-STRUCTURES OF COPPER(II) COMPLEXES OF SOME 12-MEMBERED, AND 13-MEMBERED AND 14-MEMBERED OXATRIAZA MACROCYCLES

Electronic and ESR spectroscopic studies in aqueous solution and singl e-crystal X-ray diffraction analyses of copper(II) complexes of the fo llowing oxatriaza macrocycles have been undertaken: 1-oxa-4,7,10-triaz acyclododecane (L1), 4,7,10-trimethyl-1-oxa-4,7,10-triazacyclododecane (L2), 1-oxa-4,7,11-triazacyclotetradecane (L3), 1-oxa-4,8,12-triazacy clotetradecane (L4), and 8,12-trimethyl-1-oxa-4,8,12-triazacyclotetrad ecane (L5). The complexes for solution studies were prepared in an exc ess of NaClO4, but the bulky counter ion PF6- was added to induce crys tallization. The crystal structures of [CuL1(Br)][PF6], [CuL2(Cl)][PF6 ], [CuL4(H2O)][PF6]2.H2O and [CuL5(Cl)][PF6] were determined. The co-o rdination geometry around the copper atom in the four complexes can be described as a distorted square pyramid, but whereas the basal planes comprise the three nitrogens and the oxygen from the macrocycle in th e last two complexes, in the first two complexes they comprise the thr ee macrocyclic nitrogens and a halogen atom, bromine and chlorine resp ectively. The apical co-ordination in the latter is by the macrocyclic oxygen, but in [CuL4(H2O)][PF6]2.H2O it is the oxygen of a water mole cular and in [CuL5(Cl)][PF6] it is a chlorine atom. The main conclusio ns on the structures of these complexes from spectroscopic measurement s and X-ray studies are in good agreement. However, for the complex of the 13-membered macrocycle (L3) published X-ray results point to a st ructure similar to those found in this work for the 14-membered macroc yclic complexes, while the spectroscopic studies now reported indicate a structure with a pronounced tetrahedral distortion similar to that observed in the 12-membered macrocyclic complexes. The replacement of hydrogen atoms by methyl groups on the nitrogen atoms does not affect the overall final geometry of these complexes. For this series of macr ocyclic complexes, the smaller the ligand the more pronounced is the f olding necessary to accomodate the metal at its centre. The structure of a complex of a 12-membered macrocycle having four donor atoms one o f which approaches the metal from the apical position is reported for the first time.