TERNARY COMPLEXES IN SOLUTION PART 59 - STABILITY OF BINARY AND TERNARY COPPER(II) COMPLEXES OF THE DIPHOSPHATE ANALOG, METHYLPHOSPHONYLPHOSPHATE, IN AQUEOUS-SOLUTION

The stability constants of the 1.1 complexes formed between Cu2+ or Cu (Arm)(2+), where Arm = 2,2'-bipyridyl or 1,10-phenanthroline, and meth ylphosphonylphosphate (MePP3-), CH3-P(O)(2)(-)-O-PO32-, were determine d by potentiometric pH titration in aqueous solution (25 degrees C: I = 0.1 M, NaNO3). It is shown that the equilibrium, Cu(Arm)2+ + Cu(MePP )(-) reversible arrow Cu(Arm)(MePP)- + Cu2+, is considerably displaced to its right-hand side, i.e, Delta log K = log K-Cu(Arm(MePP))(Cu(Arm )) -log K-Cu(MePP)(Cu) similar or equal to 0.45. This value is signifi cantly larger than the estimate based on statistical considerations, i .e. Delta log K-Cu/stat similar or equal to -0.9, but it agrees with p revious observations made for mixed ligand complexes formed by a dival ent transition metal ion, a heteroaromatic N base and an O donor ligan d. These results will now allow evaluation of complex stabilities of c orresponding complexes formed with nucleoside diphosphates. (C) 1998 E lsevier Science S.A. All rights reserved.