Search

Systematic theoretical studies of the [XMYH]n inorganic rings and clusters (M = AI, Ga, In; Y = N, P, As; X = H, F, CI, Br, I; n = 1–6) have been carried out using hybrid Hartree—Fock density functional theory. A consistent set of the structural and thermodynamic properties has been obtained. The stability of the MY bond decreases in the order AI > Ga ≥ In; N » P > As. Terminal groups X have a minor influence on the subsequent elimination enthalpies of the clusters. In the case of X = H, hydrogen elimination makes formation of the [HMYH]6 oligomers from MH3 and YH3 thermodynamically favorable; while in the case of halide substituents, formation of [XMYH]6 is thermodynamically unfavorable, except for the system with the strongest MY bond (AIN). Substitution of the acidic hydrogen by X is favorable energetically for all [HMYH]6 clusters, but is complicated by the processes of cluster destruction to form the [X2MYH2]2 dimers. The high stability of the [HMNH]6 clusters makes them attractive single- source precursors for the production of 13–15 composites. [ABSTRACT FROM AUTHOR]

It is widely thought that the oligomer compounds [RMYR]n (Mgroup 13, Y-group 15 element) should obey the isolated square rule found for the boron-nitrogen cages. In contrast to these expectations, the needle-shaped oligomers, which violate this rule, are more stable compared to the cage (fullerene-like) oligomers for all MY pairs (M = B, Al, Ga, In; Y = N, P, As). The stability of the needle-shaped clusters improves with increasing oligomerization degree. Thus, the isolated square rule, which is analogous to the isolated pentagon rule widely applied for fullerenes, should not serve as the basis for searches for the most stable structures of the inorganic oligomers. Generation of the needle-shaped oligomers from the group 13 and 15 hydrides is thermodynamically favorable. A synthesis of novel inorganic polymers, formed by fusion of trimeric M3Y3 rings, is expected to be viable. [ABSTRACT FROM AUTHOR]

Presents the results of an ab initio molecular orbital study of the hexamethylchalcogens confined to S6 symmetry. Determination of stationary points; Energy characteristics of the stationary points; Nuclear repulsion and molecular orbital bonding considerations.

Systematic computational studies of stannylene derivatives SnX2/SnXY and XSnR/SnR2/RSnR' were carried out using density functional theory. The basis sets used for H, F, Cl, Br, C, Si, and Ge atoms are of double-ζ plus polarization quality with additional s- and p-type diffuse functions, denoted DZP++. For the iodine and tin atoms, the Stuttgart-Dresden basis sets, with relativistic small-core effective core potentials (ECP), are used. All geometries are fully optimized with three functionals (BHLYP, BLYP, and B3LYP). Harmonic vibrational wavenumber analyses are performed to evaluate zero-point energy corrections and to determine the nature of the stationary points located. Predicted are four types of neutral-anion separations, plus adiabatic ionization energies (EIE) and singlet-triplet energy gaps (ΔES-T). The dependence of all three energetic properties upon choice of substituent is remarkably strong. The EAad(ZPVE) values (eV) obtained with the B3LYP functional range from 0.70 eV [Sn(CH3)2] to 2.36 eV [SnI2]. The computed EIE values lie between 7.33 eV [Sn(SnH3)2] and 11.15 eV [SnF2], while the singlet-triplet splittings range from 0.60 eV [Sn(SnH3)2] to 3.40 eV [SnF2]. The geometries and energetics compare satisfactorily with the few available experiments, while most of these species are investigated for the first time. Some unusual structures are encountered for the SnXI+ (X = F, Cl, and Br) cations. The structural parameters and energetics are discussed and compared with the carbene, silylene, and germylene analogues. [ABSTRACT FROM AUTHOR]

The trinuclear derivative Fe3(C8H8)3 was synthesized in 2009 by Lavallo and Grubbs via the reaction of Fe(C8H8)2 with a bulky heterocyclic carbene. This fascinating structure is the first example of a derivative of the well-known Fe3(CO)12 in which all 12 carbonyl groups have been replaced by hydrocarbon ligands. The density functional theory predicts a structure having a central Fe3 equilateral triangle with 2.9 Å Fe-Fe single bonded edges bridged by η5,η3-C8H8 ligands. This structure is close to the experimental structure, determined by X-ray crystallography. The related hypoelectronic MNi3(C8H8)3 derivatives (M = Cr, V, Ti) are predicted to have central scalene M3 triangles with edge lengths and Wiberg bond indices (WBIs) corresponding to one formal single M-M bond, one formal double M-M bond, and one formal triple M≡M bond. For Mn3(C8H8)3, both a doublet structure with one Mn-Mn double bond and two Mn-Mn single bonds in the Mn3 triangle, and a quartet structure with two Mn-Mn double bonds and one Mn-Mn single bond are predicted. The hyperelectronic derivatives MNi3(C8H8)3 have weaker direct M-M interactions in their M3 triangles, as indicated by both the M-M distances and the WBIs. Thus, NiNi3(C8H8)3 has bis(trihapto) η3,η3-C8H8 ligands bridging the edges of a central approximately equilateral Ni3 triangle with long Ni…Ni distances of ~3.7 Å. The WBIs indicate very little direct Ni-Ni bonding in this Ni3 triangle and thus a local nickel environment in the singlet Ni3(C8H8)3 similar to that observed for diallylnickel (η3-C3H5)2Ni. [ABSTRACT FROM AUTHOR]

The structure of Fe3(BF)3(CO)9 is predicted to be very different than that of any of the isoelectronic homoleptic M3(CO)12 derivatives (M = Fe, Ru, Os). Thus the lowest energy Fe3(BF)3(CO)9 structure by 19 kcal/mol has μ3-BF groups bridging the top and bottom of the Fe3 triangle with a third edge-bridging BF group in addition to nine terminal carbonyl groups. No analogous M3(CO)12 structures are found with μ3-CO groups bridging the M3 triangle. Higher energy Fe3(BF)3(CO)9 structures with two edge-bridging μ-BF groups and one terminal BF group are also found, analogous to the experimentally known Fe3(CO)12 structure. However, these structures are transition states leading to local minima with one unsymmetrical face-bridging μ3-BF group, one edge-bridging μ-BF group, and one terminal BF group. No Fe3(BF)3(CO)9 structures are found with exclusively terminal BF and CO groups analogous to the known structures of M3(CO)12 (M = Ru, Os). These studies suggest that the BF group has a significantly greater tendency than the CO group to bridge two or three metal atoms, probably owing to the reluctance of the fluorine of the BF ligands to be a part of a formal double or triple bond. [ABSTRACT FROM AUTHOR]

The relative energetics of four XH(2)O(2) (X = C, Si, Ge, Sn, Pb) isomers, dihydroxycarbene, formic acid, dioxirane, and hydroperoxycarbene, were determined using the BLYP and B3LYP density functionals with DZP and TZ2P basis sets, as well as CCSD and CCSD(T) single-point energies at the BLYP/TZ2P optimized geometries. Relative to dihydroxycarbene, formic acid was 41.8 kcal/mol lower in energy while dioxirane and hydroperoxycarbene were 51.3 and 63.6 kcal/mol higher, respectively, with CCSD(T). Furthermore, using an effective core potential (ECP) the dihydroxy congener was shown to be the most stable isomer for X = Si-Pb. The formic acid and dioxirane congeners become increasingly less stable as one descends group 14. Our results show that divalency is preferred for Si-Pb (dihydroxy congeners are the most stable) but the tetravalent formic acid congeners remain more stable than the hydroperoxy congeners, showing that divalency is not universally preferred among these isomers.

Rings of four-coordinate aluminum and nitrogen are easily synthesized and well studied, as are clusters of four-coordinate Al and N. Only recently, however, have rings that are derivatives of the model compounds (HAl-NH)(n)() (n = 2, 3) with three-coordinate Al and N been synthesized. Ab initio investigations of the structure, bonding, vibrational spectra, and reaction energies for the three-coordinate ring (HAl-NH)(2), the four-coordinate ring (H(2)Al-NH(2))(2), and the four-coordinate cluster (HAl-NH)(4) are presented. Even in the absence of differences in steric factors, the four-membered ring has longer Al-N bonds than either the six-membered ring or the unassociated aluminum amide, H(2)Al-NH(2). This is due to both rehybridization and pi interactions. Theoretical reaction energies for formation of the (HAl-NH)(4) cluster from the (H(2)Al-NH(2))(2) ring are consistent with intermolecular loss of hydrogen, or the necessity of surface catalysis.