The reaction of a Cu(II) salt, 2,2'-bipyridine (bipy), and Na4P2O7. 4H(2)O in aqueous solution affords the novel dinuclear complex {[(bipy)Cu(H2O)](2)(mu -P2O7)]. 7H(2)O} (1), where pyrophosphate adopts a bis-bidentate bridging mode; the weak antiferromagnetic coupling through the pyrophosphate bridge in 1 (J = -20 cm(-1); H = -J (S) over cap (1).(S) over cap (2)) is much increased in its fully anhydrous phase (J = -110 cm(-1)).