Synthesis, characterization and magnetic properties of a dinuclear complex [Cu(2,2′-bpy)(HL)(L)]2(NO3)2·(H2O)3/2 and a 1D chain {[Cu(2,2′-bpy)(4,4′-bpy)1/2(L)](ClO4)·(1/2H2O)}n (L is p-aminobenzoate)