Structural changes in the series of boron-carbon mixed clusters C(x)B(10-x)- (x = 3-10) upon substitution of boron by carbon.

We report a theoretical investigation on the ten-atom boron-carbon mixed clusters C(x)B(10-x)(-) (x = 3-10), revealing a molecular wheel to monocyclic ring and linear species structural change as a function of x upon increasing the number of carbon atoms in the studied series. The unbiased searches for the global minimum structures of the clusters with x ranging from 3 to 9 were conducted using the Coalescence Kick program for different spin multiplicities. Subsequent geometry optimizations with follow-up frequency calculations at the hybrid density functional B3LYP∕6-311+G(d) level of theory along with the single point coupled-cluster calculations (UCCSD(T)/aug-cc-pVTZ//B3LYP/6-311+G(d) and RCCSD(T)/aug-cc-pVTZ//B3LYP/6-311+G(d)) revealed that the C3B7(-) and C4B6(-) clusters possess planar distorted wheel-type structures with a single inner boron atom, similar to the recently reported CB9(-) and C2B8(-). Going from C5B5(-) to C9B(-) inclusive, monocyclic and ring-like structures are observed as the most stable ones on the PES. The first linear species in the presented series is found for the C10(-) cluster, which is almost isoenergetic with the one possessing a monocyclic geometry. The classical 2c-2e σ bonds are responsible for the peripheral bonding in both carbon- and boron-rich clusters, whereas multicenter σ bonding (nc-2e bonds with n > 2) on the inner fragments in boron-rich clusters is found to be the effective tool to describe their chemical bonding nature. It was shown that the structural transitions in the C(x)B(10-x)(-) series occur in part due to the preference of carbon to form localized bonds, which are found on the periphery of the clusters. Chemical bonding picture of C10(-) is explained on the basis of the geometrical structures of the C10 and C10(2-) clusters and their chemical bonding analyses.

On the suppression mechanism of the pseudo-Jahn-Teller effect in middle E6 (E = P, As, Sb) rings of triple-decker sandwich complexes.

Quantum chemical calculations of the CpMoE(6)MoCp (E = P, As, Sb) triple-decker sandwich complexes showed that E(6) fragments in the central decks of the complexes are planar. Analysis of molecular orbitals involved in vibrational coupling demonstrated that filling the unoccupied molecular orbitals involved in vibronic coupling with electron pairs of Mo atoms suppresses the PJT effect in the CpMoE(6)MoCp (E = P, As, Sb) sandwich, with the E(6) ring becoming planar (D(6h)) upon complex formation. The AdNDP analysis revealed that bonding between C(5)H(5)(-) units and Mo atoms has a significant ionic contribution, while bonding between Mo atoms and E(6) fragment becomes appreciably covalent through the δ-type M → L back-donation mechanism.

Molecular wheel to monocyclic ring transition in boron-carbon mixed clusters C2B6⁻ and C3B5⁻.

In this joint experimental and theoretical work we present a novel type of structural transition occurring in the series of C(x)B(8-x)(-) (x=1-8) mixed clusters upon increase of the carbon content from x=2 to x=3. The wheel to ring transition is surprising because it is rather planar-to-linear type of transition to be expected in the series since B(8), B(8)(-), B(8)(2-) and CB(7)(-) are known to possess wheel-type global minimum structures while C(8) is linear.

A density functional theory study of the zero-field splitting in high-spin nitrenes.

This work presents a detailed evaluation of the performance of density functional theory (DFT) for the prediction of zero-field splittings (ZFSs) in high-spin nitrenes. A number of well experimentally characterized triplet mononitrenes, quartet nitrenoradicals, quintet dinitrenes, and septet trinitrenes have been considered. Several DFT-based approaches for the prediction of ZFSs have been compared. It is shown that the unrestricted Kohn-Sham and the Pederson-Khanna approaches are the most successful for the estimation of the direct spin-spin (SS) interaction and the spin-orbit coupling (SOC) parts, respectively, to the final ZFS parameters. The most accurate theoretical predictions (within 10%) are achieved by using the PBE density functional in combination with the DZ, EPR-II, and TZV basis sets. For high-spin nitrenes constituted from light atoms, the contribution of the SOC part to ZFS parameters is quite small (7%-12%). By contrast, for chlorine-substituted septet trinitrenes, the contribution of the SOC part is small only to D value but, in the case of E value, it is as large as the SS part and has opposite sign. Due to this partial cancellation of two different contributions, SS and SOC, the resulting values of E in heavy molecules are almost two times smaller than those predicted by analysis of the widely used semiempirical one-center spin-spin interaction model. The decomposition of D(SS) into n-center (n=1-4) interactions shows that the major contribution to D(SS) results from the one-center spin-spin interactions. This fact indicates that the semiempirical SS interaction model accurately predicts the ZFS parameters for all types of high-spin nitrenes with total spin S=2 and 3, if their molecules are constructed from the first-row atoms.

Hydrated Sulfate Clusters SO42-(H2O) n ( n = 1-40): Charge Distribution Through Solvation Shells and Stabilization.

Investigations of inorganic anion SO42- interactions with water are crucial for understanding the chemistry of its aqueous solutions. It is known that the isolated SO42- dianion is unstable, and three H2O molecules are required for its stabilization. In the current work, we report our  computational study of hydrated sulfate clusters SO42-(H2O) n ( n = 1-40) in order to understand the nature of stabilization of this important anion by water molecules. We showed that the most significant charge transfer from dianion SO42- to H2O takes place at a number of H2O molecules n ≤ 7. The SO42- directly donates its charge only to the first solvation shell and surprisingly, a small amount of electron density of 0.15| e| is enough to be transferred in order to stabilize the dianion. Upon further addition of H2O molecules, we found that the cage effect played an essential role at n ≤ 12, where the first solvation shell closes. During this process, SO42- continues to lose density up to 0.25| e| at n = 12. From this point, additional water molecules do not take any significant amount of electron density from the dianion. These results can help in development of understanding how other solvent molecules could stabilize the SO42- anion as well as other multicharged unstable anions.

Peculiar Transformations in the CxHxP4-x (x = 0-4) Series.

In the current work, we performed a systematic study of the CxHxP4-x (x = 0-4) series using an unbiased CK global minimum and low-lying isomers search for the singlet and triplet P4-C4H4 species at the B3LYP/6-31G** level of theory. The selected lowest isomers were recalculated at the CCSD(T)/CBS//B3LYP/6-311++G** level of theory. We found that the transition from a three-dimensional tetrahedron-like structure to a planar structure occurs at x = 3, where planar isomers become much more stable than the tetrahedral structures due to significantly stronger π bonds between carbon atoms in addition to increasing strain energy at the carbon atom in the tetrahedral environment.