4-(imidazol-1-y1) benzoic acid (HL, L=C(10)H(7)N(2)O(2)). Copper sulfate, and sodium azide were selected as precursors, an interesting case of magnetic field-induced change in the final product of molecule-magnetic materials was observed. Without external magnetic field, the only green single crystal G [Cu(5)(C(10)H(7)N(2)O(2))(4) (N(3))(2)(SO(4))(2)](n) was prepared, but under 0.2 T external magnetic field, the other blue violet single crystal B [Cu(C(10)H(7)N(2)O(2))(2)](n) was found beside the green single crystal G. The product prepared under magnetic field comprises ca 34% B and 66% G. It indicates that the magnetic field induction is a dominating factor to the final product of self-assembly reaction for the metal-organic complex. The experiments have suggested a kind of effective control means to fabricate new molecule-magnetic materials under mild magnetic field induction. (C) 2011 Elsevier B.V. All rights reserved.