Structure determination of picolinato-copper(II)-amine complexes

Two series of Cu(II)-picolinato complexes of 1:1 and 3:2 Cu(II)-amine/picolinate namely [Cu(L1)(pic)]ClO4 and [Cu3(L2)3(pic)2(H2O)](ClO4)4·xH2O or [Cu3(dpt)3(pic)2](ClO4)4, where pic = picolinate anion, L1 = dien (diethylenetriamine), Et2dien (N,N-diethyldiethylenetriamine), Medpt (3,3′-diamino-N-methyldipropylamine), L2 = pmedien (N,N,N′,N″,N″-pentamethyl-diethylenetriamine), TPA (tris(2-pyridylmethyl)amine), and dpt = dipropylenetriamine were synthesized and structurally characterized by electronic and IR spectroscopy. Single crystal X-ray diffraction analysis of the complex [Cu(dien)(pic)]ClO4 (1) reveals its monomeric nature whereas for [Cu3(pmedien)3(pic)2(H2O)](ClO4)4·2H2O (4), it was shown that the complex consists of two subunits of the mononuclear [Cu(pmedien)(pic)]+ and the dinuclear [Cu2(pmedien)2(pic)(H2O)]3+ cations with the perchlorate as counter ions and lattice water molecules. In the mononuclear complexes of 1 and 4 the picolinato anions act as N,O-chelating ligands, whereas N,O,O′-picolinato bridges are observed in the dinuclear [Cu2(pmedien)2(pic)(H2O)]3+ cations of 4. The aqueous visible spectra of the complexes 1-6 are consistent with five-coordinate Cu(II) species where distorted square pyramidal geometry (SP) was assigned for complexes 2-5, trigonal bipyramidal geometry (TBP) for 6 and an intermediate geometry between SP and TBP for 1.