title: Homoleptic organocobalt(III) compounds with intermediate spin.
abstract: Homoleptic organocobalt(III) compounds with formula [NBu4][Co(III)(C6X5)4] [X = F (3), Cl (4)] were obtained in reasonable yields by chemical oxidation of the corresponding divalent species [NBu4]2[Co(II)(C6X5)4] [X = F (1), Cl (2)]. The [Co(III)(C6X5)4](-)/[Co(II)(C6X5)4](2-) couples are electrochemically related by quasi-reversible, one-electron exchange processes at moderate potential: E1/2 = -0.29 (X = F) and -0.36 V (X = Cl) versus saturated calomel electrode. The [Co(III)(C6X5)4](-) anions in salts 3 and 4 show an unusual square-planar geometry as established by single-crystal X-ray diffraction methods. According to their stereochemistry, these Co(III) derivatives (d(6)) are paramagnetic non-Kramers systems with a large zero-field splitting contribution and no observable electron paramagnetic resonance (EPR) spectrum. The thermal dependence of their magnetic susceptibilities can be explained in terms of a spin-Hamiltonian formalism with S = 1 ground state (intermediate spin) and substantial spin-orbit contribution. The magnetic properties of the square-planar d(7) parent species [NBu4]2[Co(II)(C6X5)4] were also thoroughly studied both at microscopic (EPR) and macroscopic levels (alternating current and direct current magnetization measurements). They behave as S = 1/2 (low spin) systems with mainly (dz(2))(1) electron configuration and a certain degree of s-orbital admixture that has been quantified. The electronic structures of all four open-shell [Co(C6X5)4](q-) compounds (q = 1, 2) accounting for their respective magnetic properties are based on a common orbital energy-level diagram.
authors.affiliation: Instituto de Síntesis Química y Catálisis Homogénea (iSQCH) and ‡Instituto de Ciencia de Materiales de Aragón (ICMA), CSIC-Universidad de Zaragoza , C/Pedro Cerbuna 12, E-50009 Zaragoza, Spain.
authors.forename: M Angeles
authors.initials: MA
authors.lastname: García-Monforte
authors.forename: Irene
authors.initials: I
authors.lastname: Ara
authors.forename: Antonio
authors.initials: A
authors.lastname: Martín
authors.forename: Babil
authors.initials: B
authors.lastname: Menjón
authors.forename: Milagros
authors.initials: M
authors.lastname: Tomás
authors.forename: Pablo J
authors.initials: PJ
authors.lastname: Alonso
authors.forename: Ana B
authors.initials: AB
authors.lastname: Arauzo
authors.forename: Jesús I
authors.initials: JI
authors.lastname: Martínez
authors.forename: Conrado
authors.initials: C
authors.lastname: Rillo