Treatment of dicyandiamide, D-penicillamine (D-H(2)pen), and Ni-II produced a Ni-3(II) trinuclear complex, [Ni-3(D-bgpen)(2)(D-pen)] (1), as a kinetic product, which was converted to a Ni-2(II) dinuclear complex, [Ni-2(D-bgpen)(2)] (2), as a thermodynamic product by soaking the crystals of 1 in heated water. In both 1 and 2, self-assembled hydrogen-bonding 3D network structures are constructed through double hydrogen bonds between the biguanide moiety as a hydrogen-bonding donor and the carboxylate group as an acceptor.