Acta Crystallographica Section C

Crystal Structure Communications

Volume 62, Part 2 (February 2006)

metal-organic compounds

fa1176 scheme

Acta Cryst. (2006). C62, m63-m66 [ doi:10.1107/S0108270105041570 ]

Insights into crystallization mechanism: a synchrotron study of polymorphism in a cobalt acetate cluster compound

J. C. Burley and T. J. Prior

Abstract: The structure of the title compound, di- [mu] ₃-acetato-1 [kappa] ²O,O':2 [kappa] O';2 [kappa] O:3 [kappa] ²O,O'-di- [mu] ₂-acetato-1 [kappa] O:2 [kappa] O';2 [kappa] O:3 [kappa] O'-octapyridyl-1 [kappa] ³N,2 [kappa] ²N,3 [kappa] ³N-tricobalt(II) bis(hexafluorophosphate), [Co₃(C₂H₃O₂)₄(C₅H₅N)₈](PF₆)₂, consists of divalent multinuclear cations in which three Co^II ions are bridged by four [mu] ₂-acetate groups. The Co^II ions are arranged in an approximately linear manner. The bridging acetates adopt two distinct coordination geometries: one pair bridges via a single O atom and the other pair employs both O atoms. The coordination octahedron around each Co^II ion is completed by three pyridine molecules for the two outer Co^II ions and by two for the inner ion. Charge is balanced by two PF₆^- anions. Single-crystal synchrotron X-ray studies indicate the existence of two polymorphs, both triclinic, which are distinguished primarily by differences in the relative orientations of the multinuclear cations, which in form 1 are tilted with respect to each other, but in form 2 are co-parallel as a result of the central Co atom lying on an inversion centre. The results of the structural studies allow an insight into the crystallization mechanism and resultant polymorphism. They suggest that a (bidentate carboxyl)C-OH-C(pyridine) interaction exists in solution. For form 1, crystallized from pyridine, the interaction is not structure determining, as it is satisfied by interactions between solvent and solute. For form 2, crystallized from CH₂Cl₂, the interaction is between a bound acetate carboxyl group on one cation and a bound pyridine on another and is thus structure directing.

Formula: Two polymorphs of [Co₃(C₂H₃O₂)₄(C₅H₅N)₈](PF₆)₂


	Structure factor file (CIF format) (1010.8 kbytes) [ doi:10.1107/S0108270105041570/fa1176Isup2.hkl ] Contains datablock I

	Structure factor file (CIF format) (266.9 kbytes) [ doi:10.1107/S0108270105041570/fa1176IIsup3.hkl ] Contains datablock II

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