摘要
在MP2/6-311++G**水平上优化乙烯酮自由基与LiX(X=F,Cl,Br)形成锂键复合物.当卤素的电负性很强(如F元素),使得Li原子处于缺电子状态,此时,电子给体会把电子偏移向锂,形成共价性较强的锂键.而当卤素的电负性减弱时,锂键中主要成分逐渐变为离子键,并且此时锂键性质还要受电子给体影响.另外,由于HCCO为缺电子结构,电负性较弱且体积较大的卤素中的孤对电子会与HCCO之间通过静电相互作用,使得HCCO…Li—X键夹角变小,接近120°.锂键性质对HCCO…LiX(X=F,Cl,Br)复合物中Li—X的伸缩振动频率有直接影响.当锂键表现为共价性时,该频率红移,而当锂键表现为离子性时,该频率蓝移.但是,由于Cl的电负性与O的接近,C的电负性与Br接近所以,在O…Li…Cl和C…Li…Br中容易形成共振结构,导致远大于在其他复合物中的红移.
The structures and properties of lithium bond complexes HCCO…LiX（X=F,Cl,Br） have been fully studied at the MP2/6-311＋＋G（d,p） level.The halogen with strong electronegativity such as fluorine influenced the electron density of lithium atom.Thus,in HCCO…LiF,the covalence in lithium bond is shown.With the same bonding structure,the ionic valence tends to increase in turn via changing of ligating atom in order of F,Cl and Br.However,the electron-deficient property of HCCO radical is structure dependent.The electrostatic interactions between HCCO with Cl and Br are stronger than that with F atom.This could help us understand the bond angles of HCCO…Li…Cl and HCCO…Li…Br which are closed to 120°.The calculated vibrational frequencies of Li-X stretching mode indicate that the red shifts are related to the covalence of lithium bond,and the blue shift to the ionic property.Additional,the vibrational coupling leads to larger red shift in HCCO…LiCl and HCCO…LiBr than in the other complexes.
出处
《分子科学学报》
CAS
CSCD
北大核心
2011年第3期208-212,共5页
Journal of Molecular Science
