title: cis-2,2'-Bipyrimidine-bridged polynuclear complex: a stairway-like mixed-valent {Fe(4)} cluster.
abstract: We report the first example of a polynuclear discrete coordination compound exhibiting only bpym bridges and containing a first-row d transition metal. A smooth self-assembly one-pot synthetic route, starting from simply FeCl(2) and FeCl(3) hydrates, allowed us to prepare a tetranuclear Fe(4) cluster with a stairway-like structure and the formula cis-{[(H(2)O)Cl(3)Fe(III)-μ(bpym)Fe(II)Cl(2)]}(2)-μ(bpym) (1) . All spectroscopic data suggest that complex 1 is a valence-localized mixed-valent Fe(II)-Fe(III) cluster with typical Mössbauer lines for both sites, which do not change with temperature. Reflectance spectroscopy did not allow one to distinguish an intervalence charge-transfer band. However, time-dependent density functional theory (DFT) calculations predict a weak high-energy Fe(II) → Fe(III) transition. Regarding the magnetic properties, the high-spin Fe(II) and Fe(III) ions interact in a weakly antiferromagnetic way with isotropic J constants of only a few wavenumbers as derived from direct-current susceptibility and magnetization data. Broken-symmetry DFT calculations support these observations.
authors.affiliation: Institut für Anorganische Chemie und Analytische Chemie, Johannes Gutenberg-Mainz Universität, Duesbergweg 10-14, D-55099 Mainz, Germany. albores@qi.fcen.uba.ar
authors.forename: Pablo
authors.initials: P
authors.lastname: Alborés
authors.forename: Eva
authors.initials: E
authors.lastname: Rentschler
mesh_terms: D018360:Crystallography, X-Ray; D005290:Ferric Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D005296:Ferrous Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D008280:Magnetics; D008958:Models, Molecular; D056004:Molecular Dynamics Simulation; D011743:Pyrimidines / Q000737:chemistry*
chemical_list: D005290:Ferric Compounds; D005296:Ferrous Compounds; D011743:Pyrimidines