Multiple bonding in homonuclear Group 13 ethene analogues

The nature and strength of the bonding in the neutral (MR2)(2) and reduced (MR2)(2)(n)- (n = 0, 1, 2) complexes of the Group 13 elements (M = B, Al, G a or In) have been investigated using non-local density functional theory. The reduced systems are found to be genuinely multiply bonded and estimates of the pi-bond strengths suggest that these weaken considerably down the g roup and are compared with those between Group 14 elements. Formation of th e doubly reduced complexes is disfavored for the heavier elements by the re pulsion between the negatively charged centers and the weakness of the M-M pi-interaction. Calculations on Li-2[M2R4] derivatives, however, suggest th at strong solvation is the key to the successful syntheses of these systems . traits-Bending of the [M2R4](2-) anions is investigated and is predicted to increase down the group. A careful treatment of the electronic causes of this bending is reported, and differs from previous analyses of the non-cl assical shapes of isoelectronic Group 14 molecules. (C) 2000 Elsevier Scien ce S.A. All rights reserved.