The Rh Vaska-type complexes, trans-[Rh(CO)(Cl)(YR3)] (Y=Group 15 atom; R=aryl or alkyl), analogues of the well-known Vaska's complex, trans-[Ir(CO)(Cl)(PPh3)], are well behaved model systems for various catalytic systems. They readily undergo a variety of reactions e.g., iodomethane oxidative addition, typically forming alkyl species as intermediates, e.g., [Rh(Cl)(CO)(CH3)(I)(YR3) ~], reductive elimination, substitution, insertion, etc.

Trimothoprim is an API which is used against bacterial infections and inhibits dihydrofolate reductase [1]. It shows the necessary donor/acceptor groups for the complexation with glutarimide derivatives which have been selected for cocrystallization experiments because of their structural similarity with barbiturates [2]. 1:1 co-crystals between trimethoprim and three glutarimide derivatives (glutarimide [I], 3,3-dimethyl glutarimide [II] and 3,3-tetramethylene glutarimide [III]) have been successfully synthesized. All these complexes show the expected hydrogen-bond pattern (ADA/DAD with A = acceptor and D = donor). Additional N-H…N hydrogen bonds between trimethoprim molecules lead to a diverse arrangement in the crystal packing. Complex I crystallized in P2 1 /n with one complex in the asymmetric unit while complexes II and III crystallized in P-1 with one and two complexes in the asymmetric unit, respectively. The structure of complex I is characterized by the formation of rings between two complexes (generated by inversion) through N-H…O In both cases three classical hydrogen bonds connect the glutarimide with the pyrimidine-2,4-diamine fragment of trimethoprim. These complexes are centrosymmetrically bridged through a pair of N-H…N hydrogen bonds, involving the two amino groups and the pyrimidine ring nitrogen. A thorough analysis of the hydrogen bonds in each crystal as well as the differences and similarities in the crystal packing within these three complexes will give insight into the design of co-crystals. Furthermore, a comparison of the conformations of trimethoprim in different structural environments demonstrates its conformational flexibility [3]. The focus of this study was to investigate the nature of molecular donor-acceptor interactions in the solid state, using spectroscopic techniques such as IR, Raman, NMR and X-ray crystallography. Complexes of para disubstituted and 4-monosubstituted biphenyl formed with 4,4'-dinitrobiphenyl (DNBP), demonstrate intense colours, from pale yellow to dark red, upon formation. These colours are dissimilar to the colour combination of the parent compounds. Typical interactions observed in such molecular complexes include π-π interactions, hydrogen bonding, charge transfer and van der Waals interactions. Complexes of DNBP, as the host molecule, included a variety of mono-and disubstituted biphenyl donors or guests, such as dihalo, diamino, di-and monohydroxy groups[1], as well as urea with a 1:1 host:guest ratio [2] and thiourea with a 7:6 ratio. Molecular complexes formed between DNBP with difluorobiphenyl with a 3:1 ratio and DNBP with dibromobiphenyl and diiodobiphenyl, both with 4:1 ratios, showed similar packing styles. The crystal structures of these complexes showed retention of the nonplanar conformation of DNBP with a dihedral angle between the phenyl rings of around 35 O [3]. However, the dihedral angle between the phenyl rings of the diflouro-, diiodo-and dibromobiphenyl in these complexes indicate that these guests are essentially planar. The confor...