SPECIFIC NONBONDED INTERACTIONS IN THE STRUCTURES OF M(3)X(7)(4+) ANDM(3)X(4)(4+) (M=MO, W X=O, S, SE) CLUSTERS

Specific nonbonded interactions (SNI) involving the chalcogens in the structures of (mu(3)-X)(mu(2)-X(2))(3)M(3)(4+) and (mu(3)-X)(mu(2)-X)( 3)M(3)(4+) (M = MO, W;X = O, S, Se) clusters are examined. Interionic contacts significantly shorter than the sum of the van der Waals or io nic radii are formed between the X atoms of the X(2) ligands that occu py the axial position relative to the M(3) plane and the N, chalcogen, or halide of the counterion or identical ion. 3 Centrosymmetric dimer s involving the (mu(2)-X(2)) ligands are observed in the structures of several M(3)X(4)(4+) derivatives. The X...X distance in these is also much less than the sum of the van der Waals radii. These SNI often oc cur in spite of the Coulombic repulsion of similarly charged species. The SNI are classified using existing data. They play a definite role in forming of the crystal structure.