Metal-Biradical Chains from a High-Spin Ligand and Bis(hexafluoroacetylacetonato)copper(II)

Abstract

The synthesis, X-ray crystal structure, and magnetic studies of a rare example of organic/inorganic spin hybrid clusters extended in infinite ladder-type chain [Cu(C5F6HO2)2]7(C35H35N5O4)2 ([Cu(hfac)2]7(pyacbisNN)2, 2) formed by the reaction of a high spin nitronylnitroxide biradical C35H35N5O4 (pyacbisNN, 1) and bis(hexafluroacetylacetonate)copper(II) = Cu(hfac)2 are described. Single-crystal X-ray structure analysis revealed the triclinic P1̄ space group of 2 with the following parameters:  a =10.6191(4) Å, b = 19.6384(7) Å, c = 21.941(9) Å, α = 107.111(7)°, β = 95.107(8)°, γ = 94.208(0)°, Z = 2. Each repeating unit in 2 carries a centrosymmetric cyclic six spin and a linear five spin cluster with four different copper coordination environments having octahedral and square planar geometries. These clusters are interconnected to form infinite chains which are running along the crystallographic b axis. The magnetic measurements show nearly paramagnetic behavior with very small variations over a large temperature range. The magnetic properties are thus result of complex competitions of many weak ferro- and antiferromagnetic interactions, which appear as small deviations from quite linear μeff vs T dependence at low temperature. At high temperature (300−14 K), antiferromagnetic behavior dominates a little, while at very low temperature (14−2 K), a small increase of μeff was observed. The magnetic susceptibility data are described by the Curie−Weiss law [χ = C/(T − θ)] with the optimal parameters C = 4.32 ± 0.01 emuK/mol and θ = − 0.6 ± 0.3 K, where C is the Curie constant and θ is the Weiss temperature