Flattened deltahedral structures and bridging hydrogen atoms in hypoelectronic dimolybdaboranes and ditungstaboranes

•The dimetallaboranes Cp2M2Bn−2Hn−2 (M = Mo, W; n = 8–12) have been investigated using density functional theory.•Flattened oblatocloso deltahedra M–M (M = Mo, W) with M–M distances of ∼2.8 to ∼3.2 Å are found.•Structures based on closo or isocloso deltahedra with MM distances of ∼2.4 to ∼2.6 Å are found.•Three Cp2M2B9H9 (M = Mo, W) structures having two non-adjacent degree 6 metal vertices are found.•Two 8-vertex Cp2M2B6H6 structures with multiple degree 3 vertices are found.

The following four Cp2M2Bn−2Hn−2 structure types (M = Mo, W) have been found in the low-energy structures using density functional theory: (1) Flattened oblatocloso deltahedra related to the experimentally known Cp2Re2Bn−2Hn−2 structures but not as severely flattened with intradeltahedral M–M (M = Mo, W) distances of ∼2.8 to ∼3.2 Å, which are 0.15–0.30 Å less than those in their Tc and Re counterparts; (2) Structures based on closo or isocloso deltahedra with short MM distances (M = Mo, W) of ∼2.4 to ∼2.6 Å along an edge corresponding to deltahedral surface metal–metal triple bonds; (3) Three 11-vertex deltahedral Cp2M2B9H9 structures (M = Mo, W) structures having two non-adjacent degree 6 vertices occupied by the metal atoms; (4) Two 8-vertex Cp2M2B6H6 structures with multiple degree 3 vertices arising from the capping of smaller deltahedra. In many of these structures one or two of the hydrogen atoms bridge M–B or B–B edges of the deltahedron.

Graphical abstractLow energy Cp2M2Bn−2Hn−2 (M = Mo, W) structures include flattened (oblate) deltahedra similar to experimental Cp2Re2Bn−2Hn−2 structures as well as closo and isocloso structures with short MM edges suggesting deltahedral surface triple bonds. Hydrogen atoms bridging M–B or B–B deltahedral edges are found in most of these structures.Figure optionsDownload full-size imageDownload as PowerPoint slide