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The reaction of RhCl3 · 3H2O with SbPh3 (Ph, C6H5) in ethanol produced mer-[RhCl3(SbPh3)3] (1), as the main product, together with trans-[RhCl2(Ph)(SbPh3)3] (2) (R. Cini, G. Giorgi, L. Pasquini, Inorg. Chim. Acta 196 (1992) 7; A. Cavaglioni, R. Cini, J. Chem. Soc., Dalton Trans. (1997) 1149). Ways to improve the yield for 1 and 2 were a subject of further works by this laboratory during the past decade and the reactivity of the organometallic compound 2 was investigated towards a variety of bases. Long sought single crystals of 1 suitable for X-ray diffraction have been obtained from hot acetone solution. The metal centre has a pseudo-octahedral coordination environment with the three chloride anions and the three SbPh3 molecules in mer positions. The Rh–Cl bond trans to Sb is significantly weakened by the high trans influence by antimony itself. This gives the rationale for the formation of 2 from RhCl3 and SbPh3 via the preliminary formation of 1, followed by dissociation of the activated chloride anion, and the subsequent formation of the Rh–C(Ph) linkage. The reaction of 1 with 2-thio-1,3-pyrimidine (Htpym) in ethanol produces crystalline [Rh( N 1, S 2-tpym)2( N 1(Sb), S 2(Rh)-tpym)(SbPh3)] (3). Single crystals suitable for X-ray diffraction studies as obtained from ethanol/diethyl-ether contain a complex molecule and a quarter of an ethanol molecule in the asymmetric unit. Two out of three tpym− anions chelate the metal centre via the N1 and S2 atoms, whereas the third tpym− anion behaves as mono-dentate through the S2 atom only. The sixth co-ordination position is occupied by the Sb atom. Interestingly, one of the N atoms of the monodentate tpym− anion behaves as electron donor to Sb and a Sb–N linkage forms (d(Sb–N), 2.846 A). As a consequence, an unusual totally hetero-atomic five-membered co-ordination ring of the type RhSCNSb(Rh) forms. A molecular modelling analysis at the hybrid density functional level DFT-B3LYP was performed on selected co-ordination molecules.

The reaction of [RhCl2(Ph)(PPh3)2] with purine-6-thione (H2tp) in alcohol produced the title compound which consists of aggregates of [Rh(C6H5)(H1,H9-H2tp)2(PPh3)]2+ and [Rh(C6H5)(H1,H9-H2tp)(H9-Ht...

The mononuclear compounds trans-dichloro(η1-phenyl)cis-bis(pyrazine)(triphenylstibine) rhodium(III) (1), and trans-dichloro(η1-rmphenyl) N-(2-cyanoethylpyrole)trans-bis(triphenylstibine)rhodium (III) (3) were prepared from trans-dichloro(η1-phenyl)tris(triphenylstibine)rhodium(III) in ethanol. The mononuclear compounds trans-dichloro(η1-phenyl)trans-bis(pyridine)(thiazole)rhodium(III) (2) and trans-dichloro(η1-phenyl)trans-bis(pyridine)(pyrazine)rhodium(III) (4) were obtained from trans-dichloro(η1-phenyl)tris(pyridine)rhodium(III) in methanol. Compounds1 and2 were analysedvia X-ray diffraction techniques from single crystals. The four compounds were characterized by spectroscopy and elemental analysis. The coordination sphere geometry for all the complexes is octahedral; thetrans influence exerted by the phenyl ligand is responsible for a long Rh N bond distance (2.263(3)A) and of large downfield shifts for1H NMR signals. The pyrazine ligands are monodentate in both1 and4. In the solid state the pyrazine ligands do not bridge the metal centres. Compounds1 and2 are barely stable in solution at room temperature. The thiazole molecule of2 bonds the metal through the nitrogen atom whereas sulfur does not show any donating ability. An extended-Huckel analysis shows that the pyrazine ligands contribute significantly to the frontier unoccupied molecular orbitals. The atomic charges on the non-metal bound nitrogen atoms of pyrazine ligands is −0.175 e in agreement with a bridging ability between two metal centres for this ligand.

Nitrile complexes of platinum easily hydrolyze to amidate, amide, and mixed amide–nitrile complexes. The amide ligands generally adopt the enol tautomeric form and coordinate to platinum through nitrogen. A mixed amide–nitrile complex, trans-[PtCl2{HN=C(OH)C(CH3)3}{N≡CC(CH3)3}] (trans-3), has shown to be the complex previously formulated as a platinum(IV) dichlorobisamidate derivative having the two amidate ligands in different tautomeric forms. The structure of trans-3 has been solved by single-crystal diffraction. The complex crystallizes in the Pbcn space group. The crystal structure has strong similarities with that previously reported by some of us for trans-[PtCl2{HN=C(OH)C(CH3)3}2] [R. Cini, F.P. Fanizzi, F.P. Intini, C. Pacifico, G. Natile, Inorg. Chim. Acta 264 (1997) 279]. Triplets of complex molecules are stabilized by intra-molecular hydrogen bonds involving N, Cl and O atoms.