Abstract
A large number of metallaborane clusters and their derivatives with various structural arrangements are known. Among them, M2B5 clusters and derivatives constitute a significant class. Transition metals present in these species span from group 4 to group 7. Their structure can vary from oblatonido, oblatoarachno, to arachno type open structures. Many of these clusters appear to be hypoelectronic and are often considered as ‘rule breakers’ with respect to the classical Wade–Mingos electron counting rules. This is due to their unique highly oblate (flattened) deltahedral structures featuring a cross-cluster M−M interaction. Many theoretical calculations were performed to elucidate their electronic structure and chemical bonding properties. In this review, the synthesis, structure, and electronic aspects of the transition metal M2B5 clusters known in the literature are discussed. The chosen examples illustrate how, in synergy with experiments, computational results can provide additional valuable information to better understand the electronic properties and electronic requirements which govern their architecture and thermodynamic stability.
Highlights
Chemists know how the electronic structure and geometry of molecules are strongly imbricated.In essence, the electron count governs the shape of molecules because it relates to the closed-shell principle [2]
We focus on the fundamental aspects, i.e., the synthesis, structure, electronic properties, and chemical bonding of these different structural types (I–IV) of M2 B5 dimetallaborane clusters and their derivatives
Fehlner pioneered the development of metallaborane chemistry a few decades ago
Summary
Chemists know how the electronic structure and geometry of molecules are strongly imbricated. This suggests that mixed main-group–transition metal clusters can be rationalized with the isolobal analogy and the same electron counting rules Both the closo-[B10 H10 ]2− borane [13,14,15] (11 seps or 42 cves) and the metallaborane cluster (CpNi) B8 H8 (Cp = C5 H5 ) [16] (11 seps or 62 cves) adopt the same ten-vertex bicapped square-antiprismatic closo structure. Even more hypoelectronic species (n − 3 seps) with highly oblate (flattened) structures called oblatocloso deltahedra in contrast to spherical or prolate geometry [21], were discovered [22,23] and rationalized [24,25,26,27,28,29] In these structures, the metal atoms are generally highly connected and occupy opposite vertices in such a way, that the. We focus on the fundamental aspects, i.e., the synthesis, structure, electronic properties, and chemical bonding of these different structural types (I–IV) of M2 B5 dimetallaborane clusters and their derivatives
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