Homoleptic complexes [Fe(Ln)]X-2 (L-1 = 1,1'-(alpha,alpha'-o-xylyl)-2,2'-biimidazole, L-2 = 1,1'-(alpha,alpha'-3,4-dibromo-oxyly1)-2,2'-biimidazole, L-3 = 1,1'-(alpha,alpha'-2,5-dimethoxy-o-xyly1)2,2'-biimidazole; X = BF4- or ClO4-) were synthesized by direct reactions of the Fe(II) precursor salts and bidentate ligands L-1, L-2, or L-3. All mononuclear complexes undergo gradual temperature-driven spin-crossover (SCO) between the high-spin (HS, S = 2) and low-spin (LS, S = 0) states. Complexes with ligands L-1 and L-2 synthesized in methanol exhibit complete SCO with the midpoint of the LS - I -IS conversion varying from 233 to 313 K, while complexes with ligand L-3, crystallized from an ethanol/dichloromethane mixture, exhibit incomplete SCO with the residual HS/LS ratio of similar to 1:4 for [Fe(L-3)(3)](BF4)(2) and similar to 1:1 for [Fe(L-3)(3)](ClO4)(2). Complexes with L-1 can also be recrystallized from ethanol/dichloromethane, in which case they exhibit very gradual and incomplete SCO, similar to those of the complexes with L-3. The differences in magnetic behavior have been traced back to peculiarities of molecular packing observed in the corresponding crystal structures. Density-functional theoretical calculations provide justification to the SCO behavior of these complexes, as compared to the HS-only behavior observed for the parent [Fe(bim)(3)](2+) complex with nonalkylated 2,2'-biimidazole (bim).