title: First-row transition-metal complexes based on a carboxylate polychlorotriphenylmethyl radical: trends in metal-radical exchange interactions.
abstract: We report the synthesis, crystal structures, and magnetic properties of a series of mononuclear, metal-radical complexes with first-row transition-metal ions using a new class of radical-based ligands, the polychlorinated triphenylmethyl (PTM) radicals. Crystal structures of three new PTM-based complexes of general formula M(PTMMC)2(py)4-x(H2O)x [PTMMC = PTM radical functionalized at the para position with one carboxylic group; M = Zn(II), x = 2 (1); M = Ni(II), x = 1 (2); M = Co(II), x = 1 (3)] show similar molecular structures in which mononuclear complexes are formed by an octahedral metal ion coordinated by two monodentated PTMMC units. From a magnetic point of view, these similar configurations describe a quasilinear, trimeric magnetic model (PTMMC-M(II)-PTMMC), in which the metal [Ni(II) or Co(II)]-radical magnetic-exchange coupling constants have been determined for the first time. In all of these complexes, the temperature dependence of the magnetic susceptibility reveals moderate antiferromagnetic-exchange coupling constants between the PTMMC radicals and Ni(II) (2J/kB = -47.1 K) and Co(II) ions (2J/kB = -15.2 K) based on the exchange Hamiltonian H = -2JSM(Srad1 + Srad2).
authors.affiliation: Institut de Ciència de Materials de Barcelona, CSIC, Campus Universitari de Bellaterra, 08193 Cerdanyola, Spain.
authors.forename: Daniel
authors.initials: D
authors.lastname: Maspoch
authors.forename: Neus
authors.initials: N
authors.lastname: Domingo
authors.forename: Daniel
authors.initials: D
authors.lastname: Ruiz-Molina
authors.forename: Klaus
authors.initials: K
authors.lastname: Wurst
authors.forename: Joan Manel
authors.initials: JM
authors.lastname: Hernandez
authors.forename: Francesc
authors.initials: F
authors.lastname: Lloret
authors.forename: Javier
authors.initials: J
authors.lastname: Tejada
authors.forename: Concepció
authors.initials: C
authors.lastname: Rovira
authors.forename: Jaume
authors.initials: J
authors.lastname: Veciana
mesh_terms: D002264:Carboxylic Acids / Q000737:chemistry*; D018360:Crystallography, X-Ray; D005609:Free Radicals / Q000737:chemistry; D006843:Hydrocarbons, Chlorinated / Q000737:chemistry*; D008280:Magnetics; D008958:Models, Molecular; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D028561:Transition Elements / Q000737:chemistry*
chemical_list: D002264:Carboxylic Acids; D005609:Free Radicals; D006843:Hydrocarbons, Chlorinated; D009942:Organometallic Compounds; D028561:Transition Elements