Solvent-induced reaction of rhodium(III) halide with N-heterocyclic ligands. Crystal structure of trans-dichlorotetrakis ( N-methylimidazole)rhodium(III) chloride dihydrate

Abstract

The synthesis of complexes of the type trans-[RhL 4X 2] + {L = N-alkylimidazoles ( N-RIm) [R = methyl (Me), ethyl (Et), n-propyl (Pr 0, n-butyl (Bu n)], 4(6)-hydroxypyrimidine (4(6)-hydPm); X = Cl − or Br −) is achieved by the general catalytic method involving the use of ethanol. The formation of complexes with L = N-Melm was reexamined and a new procedure has been established. The distribution of the trans-[RhL 4X 2] + and [RhL 5X] 2+ ions as reaction products strongly depends on the nature of the solvent and the structure of the ligand. We proposed that the initial product trans-[RhL 4X(sol)] 2+ produced by catalytic action of ethanol, undergoes nucleophilic substitution reactions either by halogenide anions X or by ligand molecules L, thus giving rise to the formation of trans-[RhL 4X 2] + or [RhL 3X] 2+ complexes. The direction of the nucleophilic substitution is determined by the concentration of ethanol, the L ligand and the X halogen. IR, Raman, electronic absorption and 1H NMR spectra were used to characterize the complexes. The prepared complexes show significant antifungal activity. The crystallographic structure of rans-[Rh( N-Melm) 4Cl 2]Cl·2H 2O has been determined. The octahedron is slightly distorted since it has, in a square plane, four nitrogen ligands and two Cl atoms at the two apical sites. The octahedral bond angles are very close to the ideal values and are in the range of 88.1(1)–89.6(1)°. The Rh atom is located on the two-fold rotation axis which relates two pairs of N-methylimidazole molecules and Cl atoms.