Synthesis, structural and magnetic properties of a series of copper(ii) complexes containing a monocarboxylated perchlorotriphenylmethyl radical as a coordinating open-shell ligand

Abstract

A series of complexes of copper(II)-containing a perchlorotriphenylmethyl radical functionalized with a carboxylic group as a new ligand is reported. The compounds [Cu(PTMMC)₂(L)₃] (PTMMC = (tetradecachloro-4-carboxytriphenyl)methyl radical; L = (1) H₂O, (2) pyrimidine and ethanol or (3) pyridine), [Cu₂(PTMMC)₂(MeCOO)₂(H₂O)₂] (4) and [Cu(HPTMMC)₂(L)₃] (HPTMMC = α-H-(tetradecachlorotriphenyl)methane-4-carboxylic acid; L = pyridine) (5) were structurally characterized. In complexes 1, 2, 3 and 5, the copper(II) ion is coordinated to two PTMMC (or HPTMMC) units in a slightly distorted square planar surrounding, while 4 shows a paddle-wheel copper(II) dimer structure, where each Cu metal ion has four O atoms of different carboxylate groups, two of them belonging to two PTMMC radicals. The copper(II)–radical exchange couplings are antiferromagnetic for complexes 1, 2 and 3. A linear three-spin model was applied to complexes 1, 2 and 3 to give J/k_B = −24.9, −15.0 and −20.7 K, respectively. Magnetic properties of 4 show that it is one of the scarce examples of a spin-frustrated system composed of organic radicals and metal ions. In this case, experimental data were fitted to a magnetic model based on a symmetrical butterfly arrangement to give a copper(II)–copper(II) exchange coupling of J/k_B = −350.0 K and a copper(II)–radical exchange coupling of J/k_B = −21.3 K, similar to that observed for the copper(II)–radical interactions in complexes 1, 2 and 3.