The reaction between the 2,6-di(pyrazol-1-yl)-4-(bromomethyl) pyridine (L) ligand and divalent transition metal salts led to the formation of three mononuclear complexes of formula [M(L)(2)](BF4)(2)center dot xMeNO(2) [M = Fe-II (1 center dot xMeNO(2)), x = 0 and 4, M = Co-II, x = 2 (2 center dot 2MeNO(2)) and]. Static magnetic measurements highlighted thermal spin crossover at high temperature (320-340 K) for the two Fe-II solvatomorphs nevertheless both the solvation degree and crystal packing had drastic influence on the shape and width of the hysteresis loop. Thus the 1 displayed abrupt and straight (6 K) hysteresis loop while for 1 center dot 4MeNO(2) the thermal spin transition could be described as a six-step gradual transition with the widest magnetic bistability range (35 K) for this kind of complexes. Irradiation at 530 nm of 1 center dot 4MeNO(2) provoked an efficient LIESST effect at low temperature (T-LIESST = 55 K). Finally dynamic magnetic measurements of 2 center dot 2MeNO(2) shown a field-induced mononuclear Single-Molecule Magnet behavior with Delta = 14.6(4) cm(-1) and tau(0) = 6.28(8) x 10(-7) s.