The structure of tetramethylammonium carbidohexadecacarbonylhexaruthenate

Abstract

[ (CH3)4N] 2[Ru6C (CO) 16] , orthorhombic, Pnma, a = 10.144 (4), b = 19.416 (4), c = 36.942 (6) t~, Z = 8, D c = 2.217 Mg m -3, V = 7275 .5 /k 3. 3528 independent reflections have been used to refine the structure giving an R value of 0-054. The structure consists of two crystallographically non-equivalent [Ru6C(CO)16 ]2anions each having m symmetry. The average non-bridged Ru--Ru distance is 2.90 + 0 .10 /k and that of bridged R u R u is 2-85 _+ 0.02 ,/k. The central C atom is octahedrally coordinated to six Ru atoms with R u C distances ranging from 2 .038-2 .053 /t~. The structure is isostructural with the Fe analogue. Introduction. The high-yield synthesis of [(CHa)4N] 2[Ru6C(CO)~6] and its application in model studies of hydrogenation have been discussed by Bradley & Ansell (1979). Intensity data 0 6o(1). This utilized F values based on statistically reliable intensity measurements [usually >2 .0 1-5o(I)] and still resulted in a high ratio of number of reflections/number of parameters of 14 : 1. ~, scans indicated that an absorption correction was negligible. The structure was solved using a combination of direct methods, p a c k i n g considerations, Fourier and least-squares techniques. During the final cycles of refinement the Ru atoms were refined with anisotropic temperature factors and corrected for anomalous dispersion ( f ' = 1.2 e, f = + 1.1 e); the non-metal atoms were refined isotropically. The parameters for one anion were varied on alternate cycles with those of the other, and those for the cations were varied on all cycles. The temperature factors of the four * The data were collected by Molecular Structures Corporation, College Station, Texas, USA. 0567-7408/80/030726-03501.00 C atoms in the N(2) te t ramethylammonium group were held at 10 ,A,2 because they assumed large positive values in previous cycles. Using a weighting scheme where w v2 = 200 /F o for F o > 200, w v2 = 1 for 80 < F < 200, and w = Fo/80 for F o < 80, full-matrix leastsquares refinement ceased when R = 0.054, wR = 0.056. Final atomic coordinates are given in Table 1, bond lengths in Table 2.f Fig. 1 gives a stereoscopic view of the packing of the anions and cations in the four asymmetric units of the unit cell, and Fig. 2 illustrates the molecular configuration and atomic-numbering scheme applicable to either anion. Discussion. The compound is isostructural with its iron analogue [(CH3)4N]2[F%C(CO)I 6] described by Churchill & Wormald (1974). An asymmetric unit of ~f Lists of structure factors, thermal parameters and bond angles have been deposited with the British Library Lending Division as Supplementary Publication No. SUP 34902 (25 pp.). Copies may be obtained through The Executive Secretary, International Union of Crystallography, 5 Abbey Square, Chester CH 1 2HU, England.