Chemistry and physics of the novel molecular-based compound exhibiting a spontaneous magnetization below Tc = 14 K, MnCu(obbz).cntdot.1H2O (obbz = oxamidobis(benzoato)). Comparison with the antiferromagnet MnCu(obbz).cntdot.5H2O. Crystal structure and magnetic properties of NiCu(obbz).cntdot.6H2O