Employment of a New Tripodal Ligand for the Synthesis of Cobalt(II/III), Nickel(II), and Copper(II) Clusters: Magnetic, Optical, and Thermal Properties

The employment of 2-(β-naphthalideneamino)-2-(hydroxymethyl)-1-propanol (LH3) in cobalt, nickel, and copper chemistry has led to the isolation of five new metallic complexes with interesting magnetic properties. More specifically, the reaction of Co­(OAc)2·4H2O with LH3 in MeOH in the presence of NEt3 under solvothermal conditions forms the complex [CoIII2CoII3(L)2(LH)2(L′)­(OAc)]·8.5MeOH (1·8.5MeOH; L′ = monoanion of 2-hydroxy-1-naphthaldehyde), while in nickel chemistry, a similar reaction of Ni­(OAc)2·6H2O with LH3 in MeCN in the presence of NEt3 under high pressure/temperature forms the complex [NiII(LH2)2]·2MeCN (2·2MeCN). Repeating the same reaction in MeOH and switching from Ni­(OAc)2·4H2O to NiSO4·4H2O produces the complex [NiII4(HL)3(OMe)­(MeOH)3]­(SO4)0.5·2MeOH (3·2MeOH) under solvothermal conditions. Furthermore, in copper chemistry, the reaction of Cu2(OAc)4·2H2O with LH3 in the presence of NEt3 in MeOH under solvothermal conditions affords the complex [CuII4(LH)4] (4), while the same reaction under ambient temperature and pressure conditions forms [CuII4(LH)4] ·3.5MeOH·2.25H2O (5·3.5MeOH·2.25H2O). Complex 1 is a mixed-valent [CoIII2CoII3] complex, consisting of three edge-sharing [Co3] triangles. Complex 2 is a nickel­(II) monomer in which the central metal is found in an octahedral geometry, while complex 3 describes a [NiII4] cubane. Complexes 4 and 5 may be considered as structural isomers because they possess the same formulas but different topologies: 4 describes a highly distorted [CuII4(OR)4]4+ eight-membered ring, while 5 consists of a distorted [CuII43-OR)4]4+ cubane. In addition, 5 can be converted to 4 in excellent yield under solvothermal conditions. Direct-current magnetic susceptibility studies have been carried out in the 5–300 K range for complexes 1 and 35, revealing the possibility of a high-spin ground state for 1, an S = 4 ground state for 2, and diamagnetic ground states for 4 and 5.