Under solvothermal conditions, a three-dimensional mononuclear crystal AQNU-1, {[Co(H2L)(DPD)(H2O)2]·2DMA}n (H2L = 5-(bis(4-carboxybenzyl)amino)isophthalic acid, DPD = 4,4'-(2,5-diethoxy-1,4-phenylene)dipyridine) has been synthesized. The transformations of AQNU-1 to binuclear {[Co2(L)(DPD)1.5(H2O)3]·DMA·H2O}n (AQNU-2) and pentanuclear {[Co5(L)2(DPD)2(OH)2]·2H2O}n (AQNU-3) were realized by double stimulation of temperature and solvent, which were accomplished by single-crystal to single-crystal (SC-SC) reaction.