Crystal engineering using the unconventional hydrogen bond. Synthesis, structure, and theoretical investigation of cyclotrigallazane

John P. Campbell, Jen Wei Hwang, Victor G. Young, Robert B. Von Dreele, Christopher J. Cramer, Wayne L. Gladfelter

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Abstract

Cyclotrigallazane, [H2GaNH2]3, was prepared by condensing liquid ammonia onto solid trimethylamine gallane, GaH3(NMe3), at -78°C and allowing the mixture to warm to room temperature and was characterized by IR, mass spectroscopy, elemental analysis, single-crystal X-ray, and neutron powder diffraction. Single-crystal X-ray diffraction at T = -167°C established that the (GaN)3 ring was in the chair conformation. Neutron powder diffraction data collected at 25°C on the fully deuterated analogue were analyzed with Rietveld refinement to give an average bond distance for Ga-D of 1.56(3) Å and a N-D of 1.04(5) Å. The intermolecular interactions were dominated by four Ga-H···H-N unconventional hydrogen bonds per molecule that form a chain parallel to the crystallographic a axis. The crystallographically equivalent D D bond lengths are 1.97 Å. Calculations revealed that in the gas phase, twist-boat conformations are preferred over chairs for cyclotrigallazane and the related boron and aluminum compounds by 0.9 to 2.6 kcal/mol at correlated levels of electronic structure theory. For cyclotriborazane and cyclotrigallazane, calculations suggest that each H···H hydrogen bond contributes about 3 kcal/mol to the binding energy (relative to the chair monomer); this value is very slightly higher for cyclotrialumazane.

Original languageEnglish (US)
Pages (from-to)521-531
Number of pages11
JournalJournal of the American Chemical Society
Volume120
Issue number3
DOIs
StatePublished - Jan 28 1998

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