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R McLellan,
N M Boag,
K Dodds,
D Ellis,
S A Macgregor,
D McKay,
S L Masters,
R Noble-Eddy,
N P Platt, D W H Rankin,
H E Robertson,
G M Rosair,
A J Welch
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ABSTRACT: The molecular structures of 1,2-closo-P(2)B(10)H(10) (1) and 1,2-closo-As(2)B(10)H(10) (2) have been determined by gas electron diffraction and the results obtained compared with those from computation at the MP2/6-31G** level of theory. The level of agreement is good for 2 (root-mean-square [rms] misfit for As and B atoms 0.0297 Å) and very good for 1 (rms misfit for P and B atoms 0.0082 Å). In comparing the structures of 1 and 2 with that of 1,2-closo-C(2)B(10)H(12) (I) it is evident that expansion of the polyhedron from I to 1 to 2 is restricted only to the heteroatom vertices and the B(6) face to which these are bound. Following deboronation (at B3) and subsequent metallation, compounds 1 and 2 have been converted into the new metalladiheteroboranes 3-(η-C(9)H(7))-3,1,2-closo-CoAs(2)B(9)H(9) (4), 3-(η-C(10)H(14))-3,1,2-closo-RuAs(2)B(9)H(9) (5), 3-(η-C(5)H(5))-3,1,2-closo-CoP(2)B(9)H(9) (6), 3-(η-C(9)H(7))-3,1,2-closo-CoP(2)B(9)H(9) (7) and 3-(η-C(10)H(14))-3,1,2-closo-RuP(2)B(9)H(9) (8), the last three constituting the first examples of metalladiphosphaboranes. Together with the known compound 3-(η-C(5)H(5))-3,1,2-closo-CoAs(2)B(9)H(9) (3), compounds 4-8 have been analysed by NMR spectroscopy and (except for 8) single-crystal X-ray diffraction. The (11)B NMR spectra of analogous pairs of metalladiphosphaborane and metalladiarsaborane (6 and 3, 7 and 4, 8 and 5) reveal a consistently narrower (9-10 ppm) chemical shift range for the metalladiarsaboranes, the combined result of a deshielding of the lowest frequency resonance (B6) and an increased shielding of the highest frequency resonance (B8) via an antipodal effect. In crystallographic studies, compounds 3 and 5B (one of two crystallographically-independent molecules) suffer As/B disorder, but in both cases it was possible to refine distinct, ordered, components of the disorder, the first time this has been reported for metalladiarsaboranes. Moreover, whilst the Cp compounds 6 and 3 are disordered, their indenyl analogues 7 and 4 are either ordered or significantly less disordered, a consequence of both the reduced symmetry of an indenyl ligand compared to a Cp ligand and the preference of the former for a distinct conformation relative to the cage heteroatoms. Unexpectedly, whilst this conformation in the cobaltadiphosphaborane 7 is cis-staggered (similar to that previously established for the analogous cobaltadicarborane), in the cobaltadiarsaborane 4 the conformation is close to cis-eclipsed.
Dalton Transactions 06/2011; 40(27):7181-92. · 3.84 Impact Factor
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ABSTRACT: Within the independent atom scattering model, we derive an approximate formula for the rotationally and vibrationally averaged three-atom terms in the series expansion of the electron scattering cross section. This formula uses the atomic scattering factors as well as the atomic scattered wavefunctions as input, and rotational averaging is performed numerically. We compare our results to previous theoretical multiple scattering approaches for the molecules F(3), F(4), and SF(6) and to experimental data for TeF(6). Our results are consistent with those of previous calculations and inclusion of the three-atom term produces a dramatically better least squares fit of the TeF(6) data. The algorithm presented here is sufficiently fast and simple to be incorporated easily into existing electron diffraction codes.
The Journal of chemical physics 06/2008; 128(20):204304. · 3.09 Impact Factor
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Journal of the Chemical Society, Dalton Transactions, 4607-4616 (2002).
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ABSTRACT: The molecular structure of Cu(1,5-cod)(hfac) in the gas phase has been determined by electron diffraction, restrained by parameters calculated ab initio (MP2/AE1 level) or using Density Functional Theory (BP86/AE1 level). The most stable structure is one in which one olefinic group of the cyclooctadiene ligand is coordinated to the square-planar copper atom [refined Cu-C distances 194.0(13) and 194.4(9) pm]. The second C=C double bond is weakly associated with the copper atom [Cu...C distances 267.2(23) and 276.9(25) pm], and the cyclooctadiene ligand has a twist-boat conformation, so that the complex has C, symmetry. The nature of the bonding between copper and each of the two olefin moieties has been assessed by topological analysis of the BP86/AE1 total electron density. A form with C symmetry, lying between 2 and 7 kJ mol(-1) above the ground state, is a transition state for exchange of the two olefinic groups. There are also two higher energy conformers, both 10 kJ mol(-1) or more above the ground state. In one of these the cyclooctadiene ligand retains the twist-boat conformation, but the Cu(hfac) moiety is coordinated in the exo position with respect to the noncoordinated olefin, instead of endo, as in the most stable conformer. The molecular symmetry is C-1 in this isomer. In the remaining form the ligand has the chair conformation, and the molecular symmetry is C-s.
Journal of the American Chemical Society, v.124, 8078-8084 (2002).
