Low-lying electronic states in µ-phenolato copper(II) binuclear compounds with hydroxo, ethanolato, azido, and cyanato exogenous bridges: crystal structures, magnetic properties, and interpretations

Abstract

Four novel µ-phenolato copper(II) binuclear complexes with exogenous bridges were synthesized, namely [Cu₂L³(X)][CLO₄]₂, X = N₃(1) or OCN (2) and [Cu₂L⁴(X)][ClO₄]₂·H₂O, X = C₂H₅O (3) or N₃(4), L³ is the binucleating ligand 4-methyl-2,6-bis[N-(2-pyridylethyl)formimidoyl]phenolate and L⁴= 4-methyl-2,6-bis[N-(2-methylthioethyl)formimidoyl] phenolate. The four crystal structures were determined. Compounds (1) and (2) are ismorphous: space group Cc, a= 12.723(9) and 12.773(5), b= 32.125(7) and 32.167(5), c= 8.987(7) and 8.980(4)Å, β= 130.39(5) and 130.35(5)° and Z= 4. Compounds (3) and (4) are not isomorphous but have rather similar structures: space group P2₁/c, a= 9.346(2) and 9.669(2), b= 32.517(4) and 30.860(4), c= 8.886(6) and 8.717(3)Å, β= 97.04(3) and 98.08(2)°, and Z= 4. In (1)–(4), the copper(II) ions of the binuclear unit are bridged by thge phenolic oxygen atom and by the exogenous ligand X in an end-on fashion. In (3), OCN^– bridges by its oxygen atom. In (1) and (2) the copper(II) is in a classical 4 + 2 environment but in (3) and (4) this environment is strongly distorted with the sulphur atom displaced by ca. 0.6 Å from the basal plane. The magnetic properties of compounds (1)–(4) were investigated and revealed a spin-singlet ground state in all cases. The singlet–triplet energy gaps were found as –278(2) for (1), –12.9(3) for (2), –850(10) for (3) and –408(4) cm^–1 for (4). The low-lying states in µ-phenolato compounds with exogenous ligands are discussed.