THE COBALTICINIUM CATION [CO-III(ETA(5)-C5H5)2]+ - A METAL-ORGANIC COMPLEX AS A NOVEL TEMPLATE FOR THE SYNTHESIS OF CLATHRASILS

The cobalticinium cation [Co(III)(eta5-C5H5)2]+ = Cocp2+ is the first metal-organic complex that acts as a structure-directing template in the hydrothermal synthesis of microporous solids. Three different clathrasil framework structures - nonasil (NON), octadecasil (AST) and dodecasil 1H (DOH) - crystallize during hydrothermal treatment from the synthesis system SiO2-NH4F-Cocp2PF6-H2O at 420-470 K. From infrared, optical and x-ray absorption (XANES, EXAFS) spectroscopic measurements, it is evident that the cobalticinium cation remains unchanged upon incorporation into the crystallizing silica framework proving its role as a template. Thermal analysis demonstrates that Cocp2+ entrapped in silica frameworks possesses a much higher thermal stability than the cation in simple salts. An X-ray single-crystal structure determination of cobalticinium nonasil was performed at 220 K: [Cocp2F4 . 88SiO2, orthorhombic, space group Pccn, a = 22.125(2) angstrom, b = 13.612(3) angstrom, c = 14.889(2) angstrom, Z = 1. Each of the large [5(8)6(12)]-cages of the nonasil structure is occupied by a Cocp2+ cation in staggered conformation which does not show any orientational or rotational disorder but is fixed due to steric confinement and weak C-H ... O(host) interactions. Fluoride anions that compensate the charge of the Cocp2+ cations reside in half of the small [4(1)5(8)] cages in front of the four-membered rings. They coordinate to the neighbouring framework atom Si1 (d(Sil-F): 1.836(6) angstrom), causing a distortion of the tetrahedral oxygen environment to a nearly ideal trigonal-bipyramidal penta-coordination of Si1.