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 (LH<sub>3</sub>) 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)<sub>2</sub>·4H<sub>2</sub>O with LH<sub>3</sub> in MeOH in the presence of NEt<sub>3</sub> under solvothermal conditions forms the complex [Co<sup>III</sup><sub>2</sub>Co<sup>II</sup><sub>3</sub>(L)<sub>2</sub>(LH)<sub>2</sub>(L′)­(OAc)]·8.5MeOH (<b>1</b>·8.5MeOH; L′ = monoanion of 2-hydroxy-1-naphthaldehyde), while in nickel chemistry, a similar reaction of Ni­(OAc)<sub>2</sub>·6H<sub>2</sub>O with LH<sub>3</sub> in MeCN in the presence of NEt<sub>3</sub> under high pressure/temperature forms the complex [Ni<sup>II</sup>(LH<sub>2</sub>)<sub>2</sub>]·2MeCN (<b>2</b>·2MeCN). Repeating the same reaction in MeOH and switching from Ni­(OAc)<sub>2</sub>·4H<sub>2</sub>O to NiSO<sub>4</sub>·4H<sub>2</sub>O produces the complex [Ni<sup>II</sup><sub>4</sub>(HL)<sub>3</sub>(OMe)­(MeOH)<sub>3</sub>]­(SO<sub>4</sub>)<sub>0.5</sub>·2MeOH (<b>3</b>·2MeOH) under solvothermal conditions. Furthermore, in copper chemistry, the reaction of Cu<sub>2</sub>(OAc)<sub>4</sub>·2H<sub>2</sub>O with LH<sub>3</sub> in the presence of NEt<sub>3</sub> in MeOH under solvothermal conditions affords the complex [Cu<sup>II</sup><sub>4</sub>(LH)<sub>4</sub>] (<b>4</b>), while the same reaction under ambient temperature and pressure conditions forms [Cu<sup>II</sup><sub>4</sub>(LH)<sub>4</sub>] ·3.5MeOH·2.25H<sub>2</sub>O (<b>5</b>·3.5MeOH·2.25H<sub>2</sub>O). Complex <b>1</b> is a mixed-valent [Co<sup>III</sup><sub>2</sub>Co<sup>II</sup><sub>3</sub>] complex, consisting of three edge-sharing [Co<sub>3</sub>] triangles. Complex <b>2</b> is a nickel­(II) monomer in which the central metal is found in an octahedral geometry, while complex <b>3</b> describes a [Ni<sup>II</sup><sub>4</sub>] cubane. Complexes <b>4</b> and <b>5</b> may be considered as structural isomers because they possess the same formulas but different topologies: <b>4</b> describes a highly distorted [Cu<sup>II</sup><sub>4</sub>(OR)<sub>4</sub>]<sup>4+</sup> eight-membered ring, while <b>5</b> consists of a distorted [Cu<sup>II</sup><sub>4</sub>(μ<sub>3</sub>-OR)<sub>4</sub>]<sup>4+</sup> cubane. In addition, <b>5</b> can be converted to <b>4</b> in excellent yield under solvothermal conditions. Direct-current magnetic susceptibility studies have been carried out in the 5–300 K range for complexes <b>1</b> and <b>3</b>–<b>5</b>, revealing the possibility of a high-spin ground state for <b>1</b>, an <i>S</i> = 4 ground state for <b>2</b>, and diamagnetic ground states for <b>4</b> and <b>5</b>.