New copper(II)-radical one dimensional chain: Synthesis, crystal structure,EPR, magnetic properties and DFT calculations

摘要

The novel chain compound [Cu(Phtfac)2(NITpPy)], (where NITpPy = 4-pyridyl-4,4,5,5-tetramethylimidazoline-l-oxy1-3-oxide and Phtfac = 4,4,4-trifluoro-l-phenylbutane-1,3-dione) wassynthesized and characterized structurally, magnetically and by EPR. The compound contains two nonequivalent Cu(II) ions, Cul and Cu2, located at inversion centers and bridged by a NITpPy ligandcoordinating Cul through the pyridine donor atom, and Cu2 through a N-0 group, resulting in ahead-to-head chain structure. The chain exhibits an unusual spin topology with two alternating pairs ofmagnetic coupling constants. The magnetic behavior was modeled considering a 16-membered ringwith alternating exchange couplings. The best fit parameters indicate a ferromagnetic (J, = 29.4 cm-1),and antiferromagnetic (J2 = –4.6 cm-') couplings and an average g = 2.05, corresponding to a groundstate with three parallel and one anti-parallel spin for each Cu,NITpPy, unit. DFT calculations allowedassigning the ferromagnetic coupling to Cu-O-NITpPy and the antiferromagnetic coupling toCu-N-NITpPy. Single crystal EPR spectra display only one resonance for most field orientations, as aconsequence of the collapse of the signals of the different spins produced by the exchange interactions.The observed g-tensor of this resonance is related to those expected for the Cu(II) and radical ions.Comparison of this compound with other Cu-NIT radicals chains bearing different substituents in theorganic radicals, highlights that the 13-diketonate ligand plays an important role in determining the finalarchitecture. Moreover, we show how a knowledge of the spin density distribution in the initial buildingblocks is essential to rationalize the magnetic behavior of the resulting product.