ESR, solid-state 31P MAS NMR, and UV–vis–NIR studies on linear CuI CuII CuI trinuclear species: Crystal structure of bis-μ-salicylato (2−)-1:2 κ4O; 2:3 κ4O-tetrakis (triphenylphosphine-1κ2P, 3κ2P)-tricopper(I, II, I), [(PPh3)2Cu]2(μ-o-OC6H4COO)2Cu

A novel neutral mixed-valence Cu(I)Cu(II)Cu(I) linear trinuclear copper metallomacrocycle [(PPh3)2Cu]2[μ-o-OC6H4COO]2Cu (3) has been synthesized and characterized. Compound 3 consists of two Cu(I) ions and one Cu(II) ion which are bridged by two salicylate (2−) ligands, and the external copper(I) atoms are coordinated by four terminal triphenylphosphines. The essentially localized mixed-valence [Cu(I)Cu(II)Cu(I)] formulation for 3 was determined on the basis of X-ray crystallography, solid-state 31P MAS NMR, and ESR spectroscopy. The solid-state 31P MAS NMR spectra of 3 is reported, affording δ[P(2)] = −1.7 ppm with 1J[Cu(I), P] = 1330 Hz and δ[P(1)] = −3.4 ppm with 1J[Cu(I), P] = 1600 Hz. UV–vis–NIR spectral measurement demonstrates the Robin–Day class II behavior of the mixed-valence compound 3 with a weak copper–copper interaction.