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 t he hydrothermal synthesis of microporous solids. Three different clath rasil framework structures - nonasil (NON), octadecasil (AST) and dode casil 1H (DOH) - crystallize during hydrothermal treatment from the sy nthesis system SiO2-NH4F-Cocp2PF6-H2O at 420-470 K. From infrared, opt ical and x-ray absorption (XANES, EXAFS) spectroscopic measurements, i t is evident that the cobalticinium cation remains unchanged upon inco rporation into the crystallizing silica framework proving its role as a template. Thermal analysis demonstrates that Cocp2+ entrapped in sil ica frameworks possesses a much higher thermal stability than the cati on in simple salts. An X-ray single-crystal structure determination of cobalticinium nonasil was performed at 220 K: [Cocp2F4 . 88SiO2, orth orhombic, space group Pccn, a = 22.125(2) angstrom, b = 13.612(3) angs trom, c = 14.889(2) angstrom, Z = 1. Each of the large [5(8)6(12)]-cag es of the nonasil structure is occupied by a Cocp2+ cation in staggere d conformation which does not show any orientational or rotational dis order 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 ato m Si1 (d(Sil-F): 1.836(6) angstrom), causing a distortion of the tetra hedral oxygen environment to a nearly ideal trigonal-bipyramidal penta -coordination of Si1.