Structure and properties of the anions MF₄⁻, MCl₄⁻and MBr₄⁻(M = C, Si, Ge)

Abstract

Density functional theory (DFT), Møller-Plesset (MP2) and coupled cluster with single and double substitutions including non-iterative triple excitations (CCSD(T)) calculations on the anions MX 4 − , with M = C, Si, Ge and X = F, Cl, Br, show that GeF 4 − , SiCl 4 − , GeCl 4 − and SiBr 4 − prefer a C 2v conformation, but CCl 4 − is an elongated C 3v structure. CBr 4 − has T d symmetry in MP2, but is slightly more stable in elongated C 3v form with DFT and CCSD(T). GeBr 4 − has T d symmetry. CF 4 − and SiF 4 − are unstable with respect to loss of an electron. Vertical electron affinities (EAs) are negative also for CCl 4 and SiCl 4 , and close to zero for GeF 4 and SiBr 4 . Adiabatic EAs range from 0.47 eV for SiCl 4 to 1.78 eV for GeBr 4 . The lowest excited states at T d symmetry are 2 T 2 resonances with energies of 2.1-3.5 eV, resulting from excitation of the a 1 singly occupied molecular orbital to vacant t 2 orbitals. Vertical excitation energies (VEEs) and vibrational frequencies are given for the most stable anionic geometries. Comparison with experimental VEEs for CCl 4 − is made. From dissociation energies of MX 4 , MX 4 − , MX 3 and MX 3 − , appearance energies of X − , MX 3 − , X 2 − and MX 2 − were calculated. Most were found to be in reasonable agreement with experimental values. Theoretical spin densities and g-factors have been compared with experimental results available for CCl 4 − , SiCl 4 − and GeCl 4 − .

Negative ion formation through dissociative electron attachment to the group IV tetrachlorides: Carbon tetrachloride, silicon tetrachloride and germanium tetrachloride

“…and Ito [128] and it is also presented in Table 4. Finally, we note that Grein et al [109] have calculated the adiabatic EA of SiCl4 at the MP2/6-311 + G(3df) level of theory and find it to be 0.47 eV. This value agrees fairly well with our B2PLYP calculations (0.40 eV) but is more than 0.3 eV higher than the value we obtain at the CCSD(T) level.…”

“…In addition, the vertical EA of GeCl4 reported by Hatano and Ito [128] is also shown in Table 6. Finally, in their calculations at the MP2/6-311 + G(3df) level of theory, Grein [109] finds the adiabatic EA of GeCl4 to be 1.43 eV, which is about 0.4 eV lower than our B2PLYP value (1.80 eV) and about 0.1 eV lower than our CCSD(T) value.…”

“…Optimized bond angles between adjacent X−Cl bonds are that of a tetrahedron; namely 109.47°. The optimized bond lengths between the central atom and the Cl atoms in CCl4 is 1.762 Å; in SiCl4 it is 2.018 Å and in GeCl4 it is 2.117 Å[109]. In order of increasing energy the occupied valence orbitals of XCl4 are expected to be; ...a1 2 , t2 6 , a1 2 , t26 , e 4 , t26 , t16…”

Combined effect of β‐nucleating agent and processing melt temperature on the toughness of impact polypropylene copolymer

“…the EPR component; the peak at about 15 • C is related to the β-relaxation of the basal hPP phase (the glass transition of amorphous PP); and the peak at about 90 • C is related to the α-relaxation of the basal PP phase, accounting for the relaxation of restricted PP amorphous chains in the crystalline phase (defects), also known as rigid amorphous molecules. 43 For βnucleated IPC (Fig. 4 (a)), as expected, the intensity of β-relaxation for samples prepared at low T p is notably higher than that of samples prepared at high T p , indicating that the chain mobility of the amorphous portion of hPP in IPC prepared at low T p was improved.…”