title: (11)B MAS NMR and First-Principles Study of the [OBO3] Pyramids in Borates.
abstract: Borates are built from the [Bϕ3] planar triangles and the [Bϕ4] tetrahedral groups, where ϕ denotes O or OH. However, the [Bϕ4] groups in some borates are highly distorted to include three normal B-O bonds and one anomalously long B-O bond and, therefore, are best described as the [OBO3] pyramids. Four synthetic borates of the boracite-type structures (Mg3B7O13Br, Cu3B7O13Br, Zn3B7O13Cl, and Mg3B7O13Cl) containing a range of [OBO3] pyramids were investigated by multifield (7.05, 14.1, and 21.1 T) (11)B magic-angle spinning nuclear magnetic resonance (MAS NMR), triple quantum (3Q) MAS NMR experiments, as well as density functional theory calculations. The high-resolution (11)B MAS NMR spectra supported by theoretical predictions show that the [OBO3] pyramids are characterized by isotropic chemical shifts δiso((11)B) from 1.4(1) to 4.9(1) ppm and nuclear quadrupole parameters CQ((11)B) up to 1.3(1) MHz, both significantly different from those of the [BO4] and [BO3] groups in borates. These δiso((11)B) and CQ((11)B) values indicate that the [OBO3] pyramids represent an intermediate state between the [BO4] tetrahedra and [BO3] triangles and demonstrate that the (11)B NMR parameters of four-coordinate boron oxyanions are sensitive to local structural environments. The orientation of the calculated unique electronic field gradient tensor element Vzz of the [OBO3] pyramids is aligned approximately along the direction of the anomalously long B-O bond, corresponding to B-2pz with the lowest electron density.
authors.affiliation: College of Materials Science and Engineering, Tongji University , Shanghai 200092, China.
authors.forename: Bing
authors.initials: B
authors.lastname: Zhou
authors.affiliation: Department of Geological Sciences, University of Saskatchewan , Saskatoon, SK S7N 5E2, Canada.|Fujian Provincial Key Laboratory of Advanced Materials, Department of Materials Science and Engineering, College of Materials, Xiamen University , Xiamen 361005, Fujian China.
authors.forename: Wei
authors.initials: W
authors.lastname: Sun
authors.affiliation: Fujian Provincial Key Laboratory of Advanced Materials, Department of Materials Science and Engineering, College of Materials, Xiamen University , Xiamen 361005, Fujian China.
authors.forename: Biao-Chun
authors.initials: BC
authors.lastname: Zhao
authors.affiliation: Fujian Provincial Key Laboratory of Advanced Materials, Department of Materials Science and Engineering, College of Materials, Xiamen University , Xiamen 361005, Fujian China.
authors.forename: Jin-Xiao
authors.initials: JX
authors.lastname: Mi
authors.affiliation: Institute of High Performance Computing, A*STAR , 1 Fusionopolis Way, No. 16-16, Connexis 138632, Singapore.
authors.forename: Robert
authors.initials: R
authors.lastname: Laskowski
authors.affiliation: Department of Chemistry, University of Ottawa , Ottawa, ON K1N 6N5, Canada.
authors.forename: Victor
authors.initials: V
authors.lastname: Terskikh
authors.affiliation: Shanghai Key Laboratory of Magnetic Resonance, East China Normal University , Shanghai 200062, China.
authors.forename: Xi
authors.initials: X
authors.lastname: Zhang
authors.affiliation: Shanghai Key Laboratory of Magnetic Resonance, East China Normal University , Shanghai 200062, China.
authors.forename: Lingyun
authors.initials: L
authors.lastname: Yang
authors.affiliation: Department of Geological Sciences, University of Saskatchewan , Saskatoon, SK S7N 5E2, Canada.
authors.forename: Sanda M
authors.initials: SM
authors.lastname: Botis
authors.affiliation: Department of Geological Sciences, University of Manitoba , Winnipeg, MB R3T 2N2, Canada.
authors.forename: Barbara L
authors.initials: BL
authors.lastname: Sherriff
authors.affiliation: Department of Geological Sciences, University of Saskatchewan , Saskatoon, SK S7N 5E2, Canada.
authors.forename: Yuanming
authors.initials: Y
authors.lastname: Pan