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Amine-Templated Aluminoborates Exhibiting Graphite and Diamond Nets

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journal contribution
posted on 03.02.2010 by Avijit Kumar Paul, Srinivasan Natarajan
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.