Boronates mononuclear structures

Boron. Boron is structurally the most bizarre element in the periodic table. Simple bonding rules that are applicable to the other elements have to be bent considerably in order to accommodate the behavior of boron. Boron should be a metal, but it is a semiconductor with unique structures and anomalous physical properties. Combined with metals it participates in metallic bonding but boron atoms are simultaneously covalently bonded to other boron atoms in the higher metal borides. Similar to carbon it does not form mononuclear ions, its halides are molecules, and its other compounds with nonmetals are solids. 

The structure of 73 was substantiated spectroscopically (5 nB = 82.5 ppm) and confirmed crystallographically. A centrosymmetric chloro-bridged dimeric structure with tricoordinate copper centers was observed. The pendant character of the borane is apparent from the rather long the B- Cu (3.05 A) and B- Cl (4.06 A) distances associated with a trigonal planar geometry around boron. Compared to related mononuclear palladium and rhodium complexes (see Section IV.B), the presence of the chloro-bridge disfavors the formation of Cl-B interactions (coordination mode F) in 73. 

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