The spin state of iron(III) in substituted N,N′-ethylenebis(salicylidenaminato) complexes of type [Fe(5-X-salen)L 2]Y, where X = CH 3O, H and Cl, L = Im and 2-MeIm and Y = Cl −, ClO − 4 and BPh − 4 was determined using X-ray structures, magnetic susceptibility and variable temperature EPR studies. X-ray data of [Fe(5-CH 3O-salen)(Im) 2]Y, where Y= ClO − 4 (1) and Cl − (2) are as follows : 1, C 24H 26N 6O 8ClFe, monoclinic P2 1\\ n, a = 10.516(4) Å, b = 13.752(3) Å, c = 19.227(3) Å, β = 102.14(2)°, V = 2718(11) Å 3, Z = 4, R = 0.097 ( R w = 0.084) ; 2, C 24H 26N 6O 4ClFe, monoclinic P2 1\\ n, a = 11.709(3) Å, b = 12.746(2) Å, c = 17.388(4) Å, β = 106.15(2)°, V = 2493(15) Å 3, Z = 4, R = 0.062 ( R w = 0.065). Metal-ligand bond distances are consistent with a HS state for iron(III) which has a tetragonally distorted octahedral geometry. Imidazole planes are coplanar and bisect the N—Fe—O bond angle in 2 while they are oriented by 77.3° apart in 1 almost coinciding with the N—Fe—O direction. Counterions showed significant effect on the overall molecular geometry and FeN 2C 2 ring. Methanolic solutions of all the complexes showed spin crossover whereas only salen and 5-Cl-salen complexes exhibited this phenomenon in solid state. EPR investigations revealed, for the first time, two types of interconvertible low spin species (LS1 and LS2) in solution ; the former was characterized by an almost axial g tensor with lower g anisotropy (2.238–1.937) while the latter with a rhombic tensor with larger g anisotropy (2.382–1.911). Ground state wave functions and distortion parameters were calculated. Structure-spin state-reactivity correlations are proposed.