title: New copper(II)-radical one dimensional chain: Synthesis, crystal structure, EPR, magnetic properties and DFT calculations.
abstract: The novel chain compound [Cu(Phtfac)(2)(NITpPy)](n) (where NITpPy = 4-pyridyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide and Phtfac = 4,4,4-trifluoro-1-phenylbutane-1,3-dione) was synthesized and characterized structurally, magnetically and by EPR. The compound contains two non equivalent Cu(II) ions, Cu1 and Cu2, located at inversion centers and bridged by a NITpPy ligand coordinating Cu1 through the pyridine donor atom, and Cu2 through a N-O group, resulting in a head-to-head chain structure. The chain exhibits an unusual spin topology with two alternating pairs of magnetic coupling constants. The magnetic behavior was modeled considering a 16-membered ring with alternating exchange couplings. The best fit parameters indicate a ferromagnetic (J(1) = 29.4 cm(-1)), and antiferromagnetic (J(2) = -4.6 cm(-1)) couplings and an average g = 2.05, corresponding to a ground state with three parallel and one anti-parallel spin for each Cu(2)NITpPy(2) unit. DFT calculations allowed assigning the ferromagnetic coupling to Cu-O-NITpPy and the antiferromagnetic coupling to Cu-N(Py)-NITpPy. Single crystal EPR spectra display only one resonance for most field orientations, as a consequence 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 the organic radicals, highlights that the beta-diketonate ligand plays an important role in determining the final architecture. Moreover, we show how a knowledge of the spin density distribution in the initial building blocks is essential to rationalize the magnetic behavior of the resulting product.
authors.affiliation: Instituto de Química, Universidade Federal Fluminense, 24020-141, Niterói, RJ, Brazil.
authors.forename: Denise A
authors.initials: DA
authors.lastname: Souza
authors.forename: Antonio S
authors.initials: AS
authors.lastname: Florencio
authors.forename: Stéphane
authors.initials: S
authors.lastname: Soriano
authors.forename: Rafael
authors.initials: R
authors.lastname: Calvo
authors.forename: Rosana P
authors.initials: RP
authors.lastname: Sartoris
authors.forename: José
authors.initials: J
authors.lastname: Walkimar de M Carneiro
authors.forename: Claudio
authors.initials: C
authors.lastname: Sangregorio
authors.forename: Miguel A
authors.initials: MA
authors.lastname: Novak
authors.forename: Maria G F
authors.initials: MG
authors.lastname: Vaz
mesh_terms: D000465:Algorithms; D003300:Copper / Q000737:chemistry*; D018360:Crystallography, X-Ray; D004578:Electron Spin Resonance Spectroscopy; D008280:Magnetics; D008968:Molecular Conformation; D009942:Organometallic Compounds / Q000138:chemical synthesis* / Q000737:chemistry; D011108:Polymers / Q000138:chemical synthesis* / Q000737:chemistry
chemical_list: D009942:Organometallic Compounds; D011108:Polymers; D003300:Copper