The copper(II) complexes [(L(n))Cu(NO3)(4) . 2(H2O)] (n = 1 : 1, n = 2 : 2) of the ammonium-functionalized ligands [6,6’-(Me(2)HNCH(2)C=C)(2)bpy](2+) (L(1)) and [6,6’-(Me(3)NCH(2)C=C)(2)bpy](2+) (L(2)) were prepared. Hydrolysis of the activated phosphodiester bis(p-nitrophenyl) phosphate (BNPP) by these complexes in ethanol-water 19:1 at 20 degrees C was investigated. The rate constants for cleavage of the bound phosphodiester at pH 6.6 are k(cat) = 4.4(+/-0.4) x 10(-3) s(-1) for (L(1))Cu and k(cat) = 4(+/-1) x 10(-6) s(-1) for (L(2))Cu. (L(1))Cu accelerates hydrolysis of BNPP 4 x 10(7)-fold and is 1000 times more reactive than (L(2))Cu. This suggests that the high reactivity of (L(1))Cu is related to the interaction of the acidic -NMe(2)H(+) group with the phosphodiester substrate. Bifunctional binding of a phosphate ester by metal coordination and hydrogen bonding with one ammonium group is observed in the crystallographically characterized complex [(L(1))(2)Cu-2(1,3-mu-O(3)POPh)(2)(OH2)(2)](NO3)(4) (3). A plausible mechanism of BNPP cleavage by (L(1))Cu includes metal-hydroxide attack to the phosphodiester which is doubly activated by coordinative and hydrogen bonding. The copper(II) complex of L(1) represents a simple model for the efficient cooperativity of metal ions and NH-acidic amino acid side chains (Lys-ammonium, Arg-guanidinium, His-imidazolium) in enzymes that catalyze the cleavage of phosphate di- and monoesters.