Theoretical characterization of electronic structures and properties of C-F···H-C pseudohydrogen bonds

The weak intermolecular interactions between 2-F-tetrahydrofuran and imidazole, pyrimidine, adenine, and guanine were studied theoretically using density functional B3LYP/6-311++G** and HF/6-311++G** methods. The results showed that both conven- tional N···H hydrogen bond and C-F···H-C pseudohydrogen bond (PHB) structures coexist in the four complexes. The weak intermolecular interaction energies indicate that the relative stabilities of the four complexes are in the order guanine···F > imidazole···F > adenine···F > pyrimidine···F. The characteristics of the four PHBs were determined using geometry optimizations, stretching vibrational frequencies, and natural bond orbital and electron density topological properties calculations. The most important result is that the F group of 2-F-tetrahydrofuran can activate the C-H to accept electrons from another molecule, and C-F···H-C PHB formation is relatively favorable.

Theoretical study on the lithium bond interaction of furan homologues C_4H_4Y (Y=O, S) with LiCH_3 via DFT and MP2

The optimizations geometries and interaction energy corrected by BSSE of the complexes between C4H4Y (Y=O, S) and CH3Li have been calculated at the B3LYP/6-311++G** and MP2/6-311++G** levels. Three complexes were obtained. Abnormally, the calculations showed that all the C10—Li14 bond lengths increased obviously but the blue-shift of C10—Li14 stretching frequency occurred after formed complexes. The calculated binding energy with basis set super-position error (BSSE) and zero-point vibrational energy corrections of complexes I―III is ?45.757, ?35.700 and ?39.107 kJ·mol?1, respectively. The analyses on the combining interaction with the atom-in-molecules theory (AIM) also showed that a relatively strong lithium bond interaction presented in furan homologues C4H4Y---LiCH3 systems. Natural bond orbital theory (NBO) analysis has been performed, and the results revealed that the com- plex I is formed with n-σ type lithium bond interaction between C4H4O and LiCH3, complex II is formed with π-s type lithium bond interaction between C4H4O and LiCH3, and complex III is formed with π-s and n-s type lithium bond interactions between C4H4S and LiCH3, respectively.

Inverse hydrogen bonds between SiH_4 and hydrides of Na,Mg and Be

The optimized geometries of the three complexes between MeH,~ （Me=Na, Mg, Be; n=1 or 2） and Sill4 have been calculated at the B3LYP/6-31 1＋＋g＊＊, MP2/6-31 1＋＋g（3df,3pd） and MP2/aug-cc-pvtz levels, respectively. The red-shift inverse hydrogen bonds （IHBs） based on Si-H, an electron donor, were reported. The calculated binding energies with basis set super-position error （BSSE） correction of the three complexes are -5.98, -8.65 and -3.96 kJ mol^-1 （MP2/6-311＋＋g（3df, 3pd））, respectively, which agree with the results obtained via MP2/aug-cc-pvtz （-6.18, -9.12 and -4.28 kJ mol^-1, respectively）. The relative stabilities of the three complexes are in the order of SiH4...MgH2 〉 SiH4...NaH 〉 SiH4...BeH2. Natural bond orbital theory （NBO） analysis and the chemical shift calculation of the related atoms revealed that the charges flow from Sill4 to MeHn and the chemical shifts of the interacting H shift to downfield. Here, the Sil-H3 of Sill4 acts as both a bond hydrogen donor and an electron donor. Therefore, compared with conventional hydrogen bonds, they formed IHB complexes. Atoms in molecules （AIM） theory have been used to investigate the topological properties of the critical points in the three IHB structures.

Theoretical characterization of single-electron iodine-bond weak interactions in CH_3…I-Y(Y=BH_2,H,CH_3,C_2H_3,C_2H,CN,NC)systems

Iodine-involved single-electron halogen bonds (SEXBs) weak interactions in the systems of CH3···I-Y(Y = BH2, H, CH3, CH==CH2, C≡CH, CN, NC) were investigated for the first time using B3LYP/6-311++G(d,p) and MP2/aug-cc-pVTZ computational levels (the relativistic effective core potential basis set of Lanl2dz was used on iodine atom). The interaction energies between two moieties with basis set super-position error corrections for the seven complexes are -0.57, -1.36, -3.80, -2.17, -4.49,-6.33 and -8.64 kJ mol-1 (MP2/aug-cc-pVTZ ), respectively, which shows that SEXBs interactions are all weak. Natural bond orbital theory analysis revealed that charges flow from CH3 to the I-Y moiety. The total amount of natural bond orbital charge transfer (ΔNC) from the CH3 radical to I-Y increases in the order CH3…IBH2 < CH3…IH ≈ CH3…ICH3 ≈ CH3···IC2H3 < CH3…ICCH< CH3…ICN< CH3…INC. Atoms-in-molecules theory was used to investigate the topological properties of the bond critical points in the seven SEXB structures.

Lithium bond structures of H_nY (n=2, 3; Y=O, S, N)… LiNH_2 and the abnormal blue shift of N―Li bond

The optimized geometries of the complexes between HnY (n=2, 3; Y=O, S, N) and LiNH2 have been calculated at the B3LYP/6-311++G** and MP2/6-311++G** levels. Three stable complexes were obtained. Frequency analysis showed that the enlarged 2N―4Li presents the abnormal blue shift in three complexes. The calculated binding energy with basis set super-position error (BSSE) and zero-point vibrational energy (ZPE) corrections of complex I―III is _58.65, _31.66 and _69.59 kJ·mol-1 (MP2), respectively. Natural bond orbital theory (NBO) analysis has been performed, and the results revealed that the H2O…LiNH2 (complex I) and H3N…LiNH2 (complex III) are formed with coexisting σ-s and n-s type lithium bond interactions, complexⅡis formed with π-s type lithium bond interaction between HnY (n=2,3; Y=O, N) and LiNH2, and H2S…LiNH2 (complex II) is formed with n-s type lithium bond interaction between H2S and LiNH2. Natural resonance theory (NRT) and atom in molecule (AIM) theory have also been studied to investigate the bond order and topological properties of the lithium bond structures.