Chiang Chi-Tung, Freindorf Marek, Furlani Thomas, DeLeon Robert L, Richard John P, Garvey James F
Department of Chemistry, University at Buffalo, State University of New York at Buffalo, Buffalo, New York 14260-3000, USA.
J Phys Chem A. 2007 Jul 12;111(27):6068-76. doi: 10.1021/jp071349c. Epub 2007 Jun 15.
The interaction between ammonia and the benzene radical cation has been investigated by gas-phase studies of mass selected ion clusters {C(6)H(6)-(NH(3))(n=0-8)}(+) via tandem quadrupole mass spectrometry and through calculations. Experiments show a special stability for the cluster ion that contains four ammonias: {C(6)H(6)(NH(3))(4)}(+). Calculations provide evidence that the first ammonia forms a weak dative bond to the cyclohexadienyl radical cation, {C(6)H(6)-NH(3)}(+), where there is a transfer of electrons from ammonia to benzene. Additional solvating ammonia molecules form stabilizing hydrogen bonds to the ring-bound ammonia {C(6)H(6)-NH(3)}(+).(NH(3))(n), which cause cooperative changes in the structure of the cluster complex. Free ammonia is a weak hydrogen bond donor, but electron transfer from NH(3) to the benzene ring that strengthens the dative bond will increase the hydrogen acidity and the strength of the cluster hydrogen bonds to the added ammonia. A progressive "tightening" of this dative bond is observed upon addition of the first, second, and third ammonia to give a cluster stabilized by three N-(+)H x N hydrogen bonds. This shows that the energetic cost of tightening the dative bond is recovered with dividends in the formation of stable cluster hydrogen bonds.
通过串联四极杆质谱对质量选择离子簇{C(6)H(6)-(NH(3))(n = 0 - 8)}(+)进行气相研究并结合计算，对氨与苯自由基阳离子之间的相互作用进行了研究。实验表明，含有四个氨分子的簇离子{C(6)H(6)(NH(3))(4)}(+)具有特殊的稳定性。计算结果表明，第一个氨分子与环己二烯基自由基阳离子{C(6)H(6)-NH(3)}(+)形成了一个弱配位键，其中有电子从氨转移到苯上。额外的溶剂化氨分子与环结合的氨{C(6)H(6)-NH(3)}(+).(NH(3))(n)形成稳定的氢键，这导致簇配合物结构发生协同变化。游离氨是一种弱氢键供体，但从NH(3)到苯环的电子转移加强了配位键，这将增加氢酸度以及簇与添加氨之间氢键的强度。在添加第一个、第二个和第三个氨时，观察到这种配位键逐渐“收紧”，形成了由三个N-(+)H x N氢键稳定的簇。这表明，收紧配位键的能量成本在稳定簇氢键的形成中得到了回报。
