Solid-State Structures of Base-Free Lithium and Sodium Tetraphenylborates at Room and Low Temperature: Comparison with the Higher Homologues MB(C6H5)4 (M = K, Rb, Cs)

Abstract

Lithium and sodium tetraphenylborate were subjected to an X-ray diffraction analysis to elucidate the solid-state structures at room (RT) and low temperature (LT). As in the potassium, rubidium, and cesium tetraphenylborates the lithium tetraphenylborate forms polymeric columns consisting of alternating Li+ and [B(C6H5)4]− ions. The lithium cations are coordinated by four η1-bonded phenyl rings of two tetraphenylborate anions. Each polymeric column is surrounded by six adjacent columns. The RT structure of sodium tetraphenylborate is almost identical with those of the heavier salts KB(C6H5)4, RbB(C6H5)4, and CsB(C6H5)4 (columns of alternating M+ and [B(C6H5)4]− ions; each column is surrounded by four adjacent columns). The LT structure of NaB(C6H5)4 is different and resembles the solid-state structure of the lithium salt. In addition, single-crystal structures of RbB(C6H5)4 (LT) and CsB(C6H5)4 (RT) have been determined for the first time at the temperature specified.