ic048955w_si_003.cif (28.46 kB)

Assembling Novel Heterotrimetallic Cu/Co/Ni and Cu/Co/Cd Cores Supported by Diethanolamine Ligand in One-Pot Reactions of Zerovalent Copper with Metal Salts

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posted on 29.11.2004, 00:00 by Dmytro S. Nesterov, Valeriya G. Makhankova, Olga Yu. Vassilyeva, Vladimir N. Kokozay, Larisa A. Kovbasyuk, Brian W. Skelton, Julia Jezierska
The three novel heterotrimetallic complexes [Ni(H2L)2][CoCu(L)2(H2L)(NCS)]2(NCS)2 (1), [Ni(H2L)2][CuCo(L)2(H2L)(NCS)]2Br2·2H2O (2), and [CuCoCd(H2L)2(L)2(NCS)Br2]·CH3OH (3) have been prepared using zerovalent copper; cobalt thiocyanate; nickel thiocyanate (1), nickel bromide (2), or cadmium bromide (3); and methanol solutions of diethanolamine in air. The most prominent feature of the structures of 1 and 2 is the formation of the “pentanuclear” aggregate {[Ni(H2L)2][CoCu(L)2(H2L)(NCS)]2}2+ made up of two neutral [CoCu(L)2(H2L)(NCS)] units and the previously unknown cation [Ni(H2L)2]2+ “glued together” by strong complementary hydrogen bonds. With Cd2+ instead of Ni2+, a different structure is obtained:  the [CoCu(L)2(H2L)(NCS)] unit is now linked to the Cd center through coordination of the oxygens of L groups on the Co atom to form the discrete heterotrimetallic molecular species 3. Cryomagnetic measurements of the compounds show that, in all cases, the magnetic behavior is paramagnetic; the polycrystalline EPR spectra contain signals due to monomeric copper species only. At the same time, the EPR spectra of frozen DMF and methanol solutions of 13 reveal the presence of triplet-state species that can be generated only by a coupling of the Cu2+ centers within a dimer. The species responsible for the appearance of transitions within the triplet state are thought to be Cu(II) dimeric centers formed by aggregation of two {CuCo(H2L)(L)2} fragments of 13 present in solution. The residual monomeric spectra in the g ≈ 2 region are indicative of the existence of an equilibrium in solution between the dimeric and monomeric Cu(II) centers in aggregated and free {CuCo(H2L)(L)2} fragments, respectively, with varying degrees of stability. The fragmentation process of 13 in solution was screened by electrospray ionization mass spectrometry.