摘要
Recently a mechanistic understanding of the pressure-and/or temperature-induced coordination change of boron in a borosilicate glass has been demonstrated by Edwards et al.In situ high-pressure ^(11)B solid-state NMR spectroscopy has been used in combination with ab initio calculations in order to obtain insight in the molecular geometry for the pressure-induced conversion.The results indicate a deformation of the B(OH)_(3) planar triangle,under isotropic stress,into a trigonal pyramid that serves as a precursor for the formation of a tetrahedral boron configuration.From our point of view,the deformation controlling the out-of-plane transition of boron accompanied with a D_(3h) into C_(3v) geometric change is an interesting transformation because it matches with our molecular description based on Van’t Hoff modelling for the tetrahedral change of carbon in CH_(3)X by substitution of X with nucleophiles via a trigonal bipyramid state in which the transferred carbon is present as a methyl planar triangle“cation”.Van’t Hoff modelling and ab initio calculations have been also applied on the dynamics of the out-of-plane geometry of a transient positively charged carbon in a trigonal pyramidal configuration into a planar trivalent carbon cation.Finally the same model is also used for the C_(3v) trigonal pyramidal configurations as NH_(3) of the group 15 elements in their nucleophilic abilities.
