Amine-templated aluminoborates exhibiting graphite and diamond nets

Abstract

A solvothermal reaction of Al₂O₃, H₃BO₃, pyridine, and H₂O at 180°C/7 days in the presence of organic amine molecules gave rise to four new aluminoborates, [(C₆H₁₈N₂) (AlB₆O₁₃H₃)], I; [(C₅H₁₆N₂)(AlB₅O₁₀)]·2H₂O, II; [(C₅H₁₆N₂)(AlB₅O₁₀)], III; and [(C₅H₁₇N₃)(AlB₅O₁₀)]·H₂O, IV, with two- and three-dimensional structures. All the structures have been formed by the connectivity involving Al³⁺ ions and [B₅O₁₀] cyclic pentaborate units. In I, the 3-connected trigonal nodes form a layer that resembles a graphite structure has been observed. The compounds II, III, and IV, have 4-connected nodes that forms a diamond related three-dimensional structure. The formation of solvatomorphs in II and III is noteworthy and has been observed first time in a family of amine templated aluminoborates. A comparison of the various aluminoborate structures reveals subtle relationships between the organic amines (length of the amines) and the final framework structures. The compounds have been characterized using a variety of techniques including IR, second-order optical behavior, and MAS NMR studies.