Effect of substituents on the strength of A-Cl- (A = Si, Ge, and Sn) bonds in hypervalent systems: ACl5-, ACl4F-, and A(CH3)3Cl2-.
The gas-phase strengths of the A-Cl(-) bonds in ACl(5)(-), ACl(4)F(-), and A(CH(3))(3)Cl(2)(-) (A = Si, Ge, and Sn) have been determined by measuring thresholds for collision-induced dissociation in a flowing afterglow-tandem mass spectrometer. Bond dissociation energies increase in the order Si < Ge < Sn. Replacement of the three equatorial chlorides with methyl groups weakens the bonds, while replacing one axial chloride with a fluoride strengthens the bonds. Computational results using the B3LYP model with several basis sets parallel the experimental periodic trends, but provide bond dissociation energies lower than experiment by 7-44 kJ mol(-1). MP2 computational results are in better agreement with experiment. The results are consistent with steric hindrance and electrostatic effects playing significant roles in the bonding energetics.
Hao
Changtong
C
Department of Chemistry and Biochemistry, Northern Illinois University, DeKalb Illinois 60115, USA.
Kaspar
Jennifer D
JD
Check
Catherine E
CE
Lobring
Kim C
KC
Gilbert
Thomas M
TM
Sunderlin
Lee S
LS
D003198:Computer Simulation; D005857:Germanium / Q000737:chemistry*; D013058:Mass Spectrometry; D009942:Organometallic Compounds / Q000737:chemistry*; D017646:Organosilicon Compounds / Q000737:chemistry*; D011789:Quantum Theory; D012825:Silicon / Q000737:chemistry*; D013816:Thermodynamics; D014001:Tin / Q000737:chemistry*
D009942:Organometallic Compounds; D017646:Organosilicon Compounds; D005857:Germanium; D014001:Tin; D012825:Silicon