A 2D iron(II) spin crossover complex, [Fe-II(HLH,Me)(2)](ClO4)(2)center dot 1.5MeCN (1), was synthesized, where HLH,Me = imidazol-4-yl-methylidene-8-amino-2-methylquinoline. 1 showed a gradual spin transition between the HS (S = 2) and LS (S = 0) states from 180 to 325 K within the first warming run from 5 to 350 K, in which 1.5MeCN is removed, and there was an abrupt spin transition at T-1/2 down arrow = 174 K in the first cooling run from 350 to 5 K. Following the first cycle, the compound showed an abrupt spin transition at T-1/2 up arrow = 185 K and T-1/2 down arrow = 174 K with 11 K wide hysteresis in the second cycle. The crystal structures of 1 were determined at 296 (an intermediate between the HS and LS states) and 150 K (LS state). The structure consists of a 2D extended structure constructed of both the bifurcated NH center dot center dot center dot O- hydrogen bonds between two ClO4- ions and two neighboring imidazole NH groups of the [Fe-II(HLH,Me)(2)](2+) cations and the pi-pi interactions between the two quinolyl rings of the two adjacent cations. Thermogravimetric analysis showed that solvent molecules are gradually eliminated even at room temperature and completely removed at 369 K. Desolvated complex 1' showed an abrupt spin transition at T-1/2 up arrow = 180 K and T-1/2 down arrow = 174 K with 6 K wide hysteresis.