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 [Co^III₂Co^II₃(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 [Ni^II(LH₂)₂]·2MeCN (2·2MeCN). Repeating the same reaction in MeOH and switching from Ni­(OAc)₂·4H₂O to NiSO₄·4H₂O produces the complex [Ni^II₄(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 [Cu^II₄(LH)₄] (4), while the same reaction under ambient temperature and pressure conditions forms [Cu^II₄(LH)₄] ·3.5MeOH·2.25H₂O (5·3.5MeOH·2.25H₂O). Complex 1 is a mixed-valent [Co^III₂Co^II₃] 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 [Ni^II₄] 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 [Cu^II₄(OR)₄]⁴⁺ eight-membered ring, while 5 consists of a distorted [Cu^II₄(μ₃-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 3–5, 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.