A new family of mononuclear [Fe-II(Rdpt)(2)-(NCE)(2)] complexes (E = S, Se, or BH3) is formed by 1:2 reaction of [Fe-II(pyridine)(4)(NCE)(2)] with the monotopic pyridyl triazole ligand 4-(4-methylphenyl)-3-(2-pyridinyl)-5-phenyl-4H-1,2,4-triazole (tolpyph). The three complexes are obtained as six different solvatomorphs: [Fe-II(tolpyph)(2)(NCS)(2)]center dot H2O (1 center dot H2O), 1 center dot 1.5CH(3)OH center dot 0.5H(2)O, [Fe-II(tolpyph)(2)(NCSe)(2)] (2), 2 center dot 1.5H(2)O, [Fe-II(tolpyph)(2)(NCBH3)(2)] (3), and 3 center dot H2O. Single-crystal X-ray diffraction reveals that 1 center dot 1.5CH(3)OH center dot 0.5H(2)O and 2 are high-spin (HS) at 100 K, while 3 is low-spin (LS) at 100 K and HS at 373 K. Compound 3 is the first structurally characterized example of an [Fe-II(Rdpt)(2)(NCE)(2)]-type complex with NCBH3 co-ligand: the crystal packing is dominated by aromatic stacking interactions. Solid-state magnetic measurements show that 1 center dot H2O and 2 center dot 1.5H(2)O remain HS down to 50 K, whereas 3 center dot H2O undergoes spin crossover (SCO) with a T-1/2 of 309 K, slightly above room temperature. A literature survey of analogous, trans-[Fe-II(Rdpt)(2)(NCX)(2)]-type complexes (53 distinct crystal structures) shows that for the complexes that are SCO active in the solid state the Fe-N equivalent to C(X) angle is usually close to straight, 162-178 degrees, whereas it is usually lower, 142-159 degrees, for the complexes that remain HS. UV-vis studies in CHCl3 solution show that in each case the use of a 6:1 ratio of tolpyph/Fe(II) is required to ensure the iron(II) is present in solution as [Fe-II(tolpyph)(2)(NCE)(2)]. Interestingly, using this ratio, all three compounds are SCO-active in CDCl3 solution-in dramatic contrast to the solid-state findings. Specifically, while compounds 1 and 2 are not SCO-active in the solid state (they remain HS), they undergo gradual SCO in CDCl3 solution, with T-1/2 values of 290 and 310 K, respectively. In CDCl3 solution, compound 3 has a T-1/2 value of 288 K, which is 21 K lower than in the solid state. These results highlight the differences between solid state (ligand field; crystal packing) and solution (ligand field; solvation) effects on SCO, with the latter studies revealing room-temperature SCO for all three of these complexes.