Synthesis and Structure of [Fe(TPA)Cl2](ClO4) and [{Fe(TPA)Cl}2O](ClO4)2 Where TPA = Tris-(2-pyridylmethyl)amine

[Fe(TPA)Cl 2 ](ClO 4 ), where TPA is tris-(2-pyridylmethyl)amine, crystallizes in the orthorhombic space group P2 1 2 1 2 1 with Z = 4, a = 8.6264(10) Å, b = 15.459(3) Å, and c = 16.008(3) Å. The structure was determined at 110 K from 4333 reflections (3520 observed) with R = 0.041 (R w = 0.082). The iron is pseudo-octahedral with the two chloride ions cis . The Fe-Cl bond trans to the tertiary amine is shorter. [{Fe(TPA)Cl} 2 O](ClO 4 ) 2 exhibits two polymorphic monoclinic forms, and the monohydrate also crystallizes in a monoclinic form. For the P2 1 /c polymorph, Z = 2, a = 10.839(2) Å, b = 15.956(3) Å, c = 12.416(2) Å, β = 107.024(10)°, and the structure was determined at 95 K from 6514 reflections (3974 observed) with R = 0.052 (R w = 0.099). For the C2/c polymorph, Z = 4, a = 20.5023(17) Å, b = 15.2711(13) Å, c = 16.1069(11) Å, β = 124.465(4)°, and the structure was determined at 161 K from 6250 reflections (3130 observed) with R = 0.0632 (R w = 0.1229). For the hydrate, P2 1 /n, Z = 4, a = 16.201(2) Å, b = 16.980(3), c = 16.451(3), β = 112.234(5)°, and the structure was determined at 100 K from 12,745 reflections (6600 observed) with R = 0.097 (R w = 0.190). In each of the [{Fe(TPA)Cl} 2 O] 2+ units, each iron is pseudo-octahedral with the chloride and oxide ions cis . The oxide bridge is linear, and the two chlorides are anti . The Fe-N distance for the pyridyl ring trans to the oxide bridge is quite long due to the trans influence of the oxide. Graphic Abstract The X-ray structures of [Fe(TPA)Cl 2 ](ClO 4 ), where TPA is tris-(2-pyridylmethyl)amine, and three polymorphs of dimeric [{Fe(TPA)Cl} 2 O](ClO 4 ) 2 are presented and discussed.