A family of cationic and neutral highly water-soluble rhodium complexes [Cp*Rh(PTA)(3)]Cl-2 (1), [Cp*RhCl2(THP)] (2), [Cp*RhCl(THP)(2)]Cl (3), and [Cp*RhCl(PTA)(THP)] Cl (4) have been synthesised and fully characterised [PTA = 1,3,5-triaza-7-phosphaadamantane; THP = tris(hydroxymethyl) phosphine]. Their water-solubility increases as the number of the phosphines coordinated to the metal centre is increased. The X-ray crystal structure of compound 2 was obtained and shows the presence of intermolecular hydrogen bonding. NMR speciation studies of [Cp*RhCl2(PTA)] in deuterated water show the existence of several equilibria involving substitution processes in which the water molecules can substitute both chloride and PTA ligands. (C) 2009 Elsevier B. V. All rights reserved.