Molybdatricarbaboranes as examples of isocloso metallaborane deltahedra with three carbon vertices

Density functional theory shows that the lowest energy CpMoC 3 B n −4 H n −1 ( n  = 8, 9, 10, 11) structures are based on isocloso or similar deltahedra with the molybdenum atom at a degree 6 vertex. Such deltahedra include the capped pentagonal bipyramid for the 8‐vertex system. Among such geometries the lowest energy structures have the carbon atoms at the lowest degree vertices (typically degree 4 vertices), no pairs of adjacent carbon atoms (i.e., no C‐C edges), and the maximum number of Mo‐C edges. Optimizing these factors favoring low‐energy CpMoC 3 B n −4 H n −1 ( n  = 8, 9, 10, 11) structures leads to a unique lowest energy structure lying more than 10 kcal/mol below the next lowest energy structure for the 8‐, 10‐, and 11‐vertex systems. However, the 9‐vertex CpMoC 3 B 5 H 8 system has three structures within 8 kcal/mol including a structure based on the closo tricapped trigonal prism rather than the isocloso 9‐vertex deltahedron. © 2015 Wiley Periodicals, Inc.