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.
ABSTRACT
This study introduces a motionless novel single vessel powder processor designed to carry out all of the unit operations in the preparation of powders for tableting. The processor used controllable fluid dynamics to provide the energy for each unit operation. The vessel design was evaluated using a computational fluid dynamics model which indicated the flow necessary for the intended processing operations to take place. The processor performance was evaluated experimentally for two unit processes: particle size reduction and dry powder mixing. The processor was found capable of reducing the size of lactose granules from a median particle diameter of 459 microm to a median particle diameter of 182 microm within 5 min under optimal process conditions. It was found that a formulation containing lactose granules (373 microm median particle diameter) and a model drug, sodium chloride (30 microm), could be mixed to an improved degree of homogeneity in comparison with equivalent powders blended using a conventional turbulent tumbling technique. It was concluded that a processor having controllable fluid dynamics offered the potential to perform multi-task processing of powders.
