Synthesis, structure and magnetic properties of [Cu4(Hmbpp)2(H2NC(O)NH2)2(H2O)8]·4H2O

[Cu4(Hmbpp)2(H2NC(O)NH2)2(H2O)8]·4H2O 1, the first example of a discrete polynuclear copper phosphonate complex isolated from aqueous media was synthesised by the addition of urea to a solution of a copper(II) salt and the bisphosphonic acid ligand 4-methyl2,6-bis(phosphonomethyl)phenol (H5mbpp). 1 contains four distorted square pyramidal copper atoms and the Cu4 units are linked by a complicated hydrogen bonded network involving co-crystallised water molecules.