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Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. Pure Appl. Chem., Vol. 75, No. 9, pp. 1315-1323, 2003. © 2003 IUPAC 1315 Evolving patterns in boron cluster chemistry* Abstract: This paper outlines the development of our knowledge and understanding of the structures and bonding of boron cluster compounds, with particular reference to the evolving complementary roles localized bonding and molecular orbital treatments have played in providing simple rationalizations of their polyhedral molecules. INTRODUCTION: EARLY DEVELOPMENTS

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The homoleptic amides [M(NMe 2 ) 5 ] (M = Nb 1 or Ta 2; the latter is characterised by a structural study) reacted with the carborane nido-C 2 B 9 H 13 to eliminate two equivalents of HNMe 2 and generate the dicarbollide half-sandwich tris(dimethylamide) complexes [M(C 2 B 9 H 11 )(NMe 2 ) 3 ] (M = Nb 3 or Ta 4). The crystal structures of isomorphous 3 and 4 have been determined and reveal two NMe 2 ligands in a vertical orientation and the third one in a horizontal orientation with respect to the η 5 -co-ordinated face of the C 2 B 9 H 11 ligand. The electronic factors responsible for the amide ligand orientations in these complexes are explored using qualitative MO arguments. Complexes 3 and 4 reacted with CO 2 and CS 2 to yield the tris(carbamateor Ta 8) complexes, respectively. The crystal structures of 6 and 7 show two (dithio)carbamate ligands in horizontal and one in vertical orientation, demonstrating the similarity between the σ,π-donor frontier orbitals of the ligands NMe 2 and X 2 CNMe 2 in 4 and 6 or 7 respectively.

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