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

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 1−3 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
1−3 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 1−3 in solution was screened
by electrospray ionization mass spectrometry.