Hygroscopic La[B5O8(OH)]NO3 • 2H2O: Insight into the evolution of borate fundamental building blocks

Borates have exceptionally diverse fundamental building blocks (FBBs), but factors controlling the formation of borate FBBs are poorly understood. The title compound La[B5O8(OH)]NO3 center dot 2H(2)O crystallizes in the space group P2(1)/n with a=6.5396(12) angstrom, b=15.550(3) angstrom, c=10.6719(19) angstrom, beta=90A4(1)degrees and Z=4 at 173(2) K. Its structure has been refined from single-crystal X-ray diffraction data to R-1=0.049 (for 2465) and wR(2)=0.173 (for 2459 I > 2 sigma(I)). This structure analysis and first-principles calculations show that the change of the FBB from 3 Delta 2 square in the title compound to 2 Delta 3 square in La[B5O8(OH)(H2O)]NO3 center dot 2H(2)O is accompanied by a rotation of the NO3 group. FTIR, Rietveld and thermal analysis results show that the hygroscopic title compound is partially changed to La[B5O8(OH)(H2O)]NO3 center dot 2H(2)O, with the conversion of [BO3] to [BO3(H2O)] by water absorption. (C) 2013 Elsevier Inc. All rights reserved.