CAI4X(X=Si,Ge):Molecules with simultaneous planar tetracoordinate carbon,aluminum,and silicon/germanium

摘要

The authors report the first theoretical study on the hexa-atomic molecules CAl4X(X=Si,Ge)at the B3LYP/6-311 + +G(2d),MP2/6-311 + + G(2d),and CCSD(T)/6-311 + +G(3df)(single point)levels.Three low-lying isomers(within 2.0 kcal/mol)can be formally viewed as constructed by one Al+ interacting with the planar(CAl3X)- at the side Al-X bond(X-1),side Al-Al bond(X-2),and central C atom(X-3).The isomers X-1 and X-2 both have planar structures that include the planar tetracoordinate carbon,aluminum,and silicon/germanium,while the three-dimensional isomer X-3 has the pentacoordinate carbon.The planarity of X-l and X-2 is ascribed to the ligand five-center two-electron bonding molecular orbital,similar to the orbital responsible for the planarity of(CAl3X)-(X=Si,Ge).Kinetically,the two planar structures X-l and X-2 can be easily interconverted to each other via the intermediate X-3,indicative of their coexistence.Of particular interest,isomer X-l represents the first example that simultaneously contains three types of planar centers in a single molecule,to the best of our knowledge.The three low-lying and structurally interesting isomers X-l,X-2,and X-3 await future experimental verification.The present results could enrich the planar chemistry.