Bond, dative calculation

All Si—N bonds in compounds where hexacoordinate silicon atom is bonded to tricoordinate nitrogen atoms are dative bonds, where the nitrogen atom provides its lone-pair electrons to the bond. The average Si — N bond was calculated from 31 individual values to be 1.969 A (s.d. 0.05 A and s.m. 0.008 A). 

PPhi) and 2556 Hz (PMes) are taken as an indication of four coordinate platinum(O). The X-ray diffraction study gave the Th-Pt distance of 2.984(1) A which was interpreted as a direct thorium platinum bond. Theoretical calculations suggest that Th-Pt bond can be regarded as a formal donor-acceptor or dative bond from the filled d shell of Pt into the empty d shell of Th. 

Acyclic phosphazenes (phosphazo derivatives, phosphine imines, phosphoranimines) continue to attract interest. A review of the three coordinate materials, RN=PR =X has appeared. " Several molecular orbital calculations have been reported. An ab initio treatment of the PN energy surface suggests that this species is best regarded as having a dative phosphorus-nitrogen double bond rather than a triple bond and the phosphonitrene, once formed,... 

DB-1) Formation of a dative bond leads to a change of formal charge at each atom (A B+), so the calculated atomic charges 0A(dat) and gB(dat) for a dative-bonded pair deviate markedly from those (( A(sep) and 0B(sep)) in the dissociated species by approximately equal and opposite amounts for A and B,... 

Ab initio theoretical cluster calculations showed that all of the products, with the exception of the O-dative bonded product, have sufficient binding energies (from 40-60 kcal/mol) to be thermodynamically stable at room temperature within the timescale of the experiments [255]. Furthermore, most of the activation barriers... 

Pyridine, a six-membered cyclic aromatic amine, has also been studied on Ge(100)-2 x 1 both theoretically [315,316] and experimentally by STM [314]. It adsorbs selectively through a Ge—N dative bond on the surface. Theoretical calculations showed that the dative-bonded adduct is more stable than other possible reaction products (e.g., cycloaddition products) on Ge [315,316]. Furthermore, STM images show formation of a highly ordered monolayer at the surface with a coverage of 0.25 ML. The pyridine overlayer forms a c(4 x 2) structure in which the molecules bind to the down atoms of every other dimer to minimize repulsive interactions between pyridine molecules. 

Hughbanks has calculated the molecular orbitals of a hypothetical 25-e [Mo6S8L5] cluster and discussed their dimerization (72). The 2eg and 2tIu o--acceptor orbitals lie above the manifold of 12 metal-metal bonding orbitals, which include some s and p hybridization acting to accentuate their projection outward from the cluster. These orbitals are strongly destabilized when the cluster is capped by donor ligands to form the dative exo M—X bonds. There remains one 2e (z2) acceptor... 

Similar results were obtained with [(CO)2(PH3)2Fe(772-E=CH2)]. For E = S a substantially larger binding energy and a more pronounced deformation of the H2C=E ligand was calculated than for E = O. It was concluded that the 77-back-donation is the main bonding interaction between the metal and the H2C=E molecule in the complexes. In the case of the thioformalde-hyde complex, a nonnegligible ligand-to-metal interaction between thioformaldehyde and iron exists.41... 

Pentacoordinate silicon forms two types of bonds with tricoordinate nitrogen atoms, a pure covalent bond and a N - Si dative bond. The first is significantly shorter than the second. The average covalent Si—N bond length in compounds where pentacoordinate silicon atom is bonded to tricoordinate nitrogen atom was calculated from 48 XRD experimental values to be 1.761 A (s.d. 0.06 A, s.m. 0.009 A). An example of the difference in bond length is shown in 127141 where the covalent Si—N bond lengths are 1.766 and 1.770 A and the dative bond is 2.333 A. 

Structure optimization of main group molecules with generic force fields has the same advantages and problems as molecular mechanics calculations of organic and organometallic compounds with similar approaches on one hand there is no need to fit a specialist force field, on the other hand is the expectation of lower accuracy1279,2801. The structural results are especially poor for molecules where electronic effects are important, e.g., those with hypervalent or dative bonds. 

The nature of bonding in the cationic metal carbonyls has been investigated by both vibrational and electronic spectroscopy, and molecular orbital calculations have been carried out these are consistent with a bonding scheme for carbon monoxide coordinated to a metal, consisting of a dative cr-bond from carbon to metal, augmented by a synergic metal-to-carbonyl dative 7r-bond (7, 57). 

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