The nitro-substituted catecholates of triphenylantimony(V): Tetragonal pyramidal vs trigonal bipyramidal coordination

The molecular and crystal structures of two nitro-substituted catecholates of antimony(V), (4-nitro-3,6-di-tert-butyl-catecholato)triphenylantimony(V) (1) and (6-nitro-3,5-di-tert-butyl-catecholato)triphenylantimony(V) (2) were determined by single-crystal X-ray analysis to reveal different coordination environments of Sb: antimony in 1 adopts a distorted tetragonal pyramidal environment while in 2 possesses a distorted trigonal bipyramidal environment in the crystal. The intermolecular H(Ph)..Sb (3.27 Å) interactions result in a formation of unusual thirty-six membered hexamolecular core of 1. In the accordance with DFT calculations, the differences in energy of the tetragonal pyramidal (TP) and trigonal bipyramidal (TB) geometries for 1 (−0.03 kcal/mol) and the energetic barrier between the TP and TB configurations (∼0.25 kcal/mol) are quite small and allow to realize the intramolecular Sb⋯H interactions with the formation of supramolecular structure in the crystal and to stabilize the TP coordination of Sb(V) in 1, while the bigger energy difference between the TP and TB configurations in 2 (2.1 kcal/mol) and the energetic barrier ∼2.0 kcal/mol stabilizes the TB coordination of Sb(V) in 2.