B_3H_7和B_3H_9分子中多中心键的研究

Studies on the Nature of Multiple-center Bonds in B3H7 and B3H9.

用Ｄｕｎｎｉｎｇ基进行从头计算的结果表明：在Ｂ＿３Ｈ＿７（１１０３）中氢桥三中心键与ＢＢＢ三中心键已用σ－共轭效应“融合”为１个四中心键，其特性为ｆ＿Ｂ１－Ｂ２＝１３．６１６２ｎＪ／ｍ，ｆ＿Ｂ２－Ｂ３＝１１．７７１１ｎＪ／ｍ，ｆ＿Ｂ－Ｈｂ－Ｂ＝２８．１３８６ｎＪ／ｍ，ｆ＿４ｃｅｎｔｅｒ＝５８．７０７１ｎＪ／ｍ。但在Ｂ＿３Ｈ＿９中３个氢桥三中心键不相互作用，保持独立，其特征为ｆ＿Ｂ－Ｂ＝４．５９６４ｎＪ／ｍ，ｆ＿Ｂ－Ｈｂ－Ｂ＝３２．３０６６ｎＪ／ｍ，ｆ＿Ｈｂ３ｃｅｎ＝４２．１３３７ｎＪ／ｍ。

As a result of AB initio study,using Dunning’s basis set,it is shown that,in B3H7(1103),the two three-center bonds have been fused into a four-center bond,owing to the σ-conjugation ef-fect.The properties in bond strength of this four-center bond are fB1-B2=13.6162 nJ/m,fB2-B3=11. 7711 nJ/m,fB-Hb-B=28. 1386 nJ/m,f4center=58.7071 nJ/m. No σ-conjugation effect can take place be-tween the three separated three-center bonds in B3H9,whose proper-ties are fB-B=4.5964 nJ/m,fB-Hb-B=32.3066 nJ/m,fHb3cen=42.1337 nJ/m.