Four new monomeric pyrophosphate complexes, namely [Co-(phen)(2)(H2P2O7)]center dot 4H(2)O (1.4H(2)O), [Ni(phen)(2)(H2P2O7)]center dot 8H(2)O (2. 8H(2)O), [Cu(Phen)(H2O)(H2P2O7)] (3) and {[Cu(phen)(H2O)(P2O7)][Na-2(H2O)(8)]}center dot 6H(2)O (4. 14H(2)O) have been isolated and structurally characterized. The impact of pH and stoichiometry in obtaining 1-4 is described. These complexes have been tested against the adriamycin-resistant ovarian cancer cell line A2780/AD, revealing highly significant (nM) IC50 values, compared to mu M IC50 values for cisplatin controls.