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

The synthesis of complexes of the type trans -[RhL 4 X 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 4 X 2 ] + and [RhL 5 X] 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 4 X(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 4 X 2 ] + or [RhL 3 X] 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 1 H NMR spectra were used to characterize the complexes. The prepared complexes show significant antifungal activity. The crystallographic structure of rans -[Rh( N -Melm) 4 Cl 2 ]Cl·2H 2 O 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.