Iron(II) Polyamine Chemistry: Variation of Spin State and Coordination Number in Solid State and Solution with Iron(II) Tris(2-pyridylmethyl)amine Complexes

The synthetic system of
Fe(SO3CF3)2 and one or
two TPA ligands (TPA = tris(2-pyridylmethyl)amine)
affords
a series of complexes that demonstrate the complexities of the
solid-state and solution coordination chemistry of
labile iron(II) even with a multidentate ligand. The low-spin
[Fe(TPA)(CH3CN)2](SO3CF3)2
(1-OTf) complex
forms in acetonitrile, but the high-spin complex
Fe(TPA)(SO3CF3)2
(2) forms in chloroform. The methanol-bound complex
[Fe(TPA)(CH3OH)2](BPh4)2
(3) forms in the presence of the noncoordinating anion,
BPh4-, and
six-coordinate
[Fe(TPA)2](SO3CF3)2
(4-OTf) and eight-coordinate
[Fe(TPA)2](BPh4)2
(4-BPh4) form in the presence
of excess ligand. Their behavior in solution is explored by
studying their magnetic properties and NMR spectra,
which indicate the presence of spin and coordination equilibria.
The crystal structures of these complexes are
reported. Crystallographic parameters are as follows.
1-OTf·CH3CN: 
C26H27F6FeN7O6S2,
monoclinic, P21/n,
a
= 12.418(2) Å, b = 16.192(4) Å, c
= 15.855(2) Å, β = 92.09(2)°, Z = 4.
2: 
C20H18F6FeN4O6S2,
monoclinic,
P21/c, a =
17.636(2) Å, b = 9.659(1) Å, c =
16.004(2) Å, β = 113.29 (1)°, Z = 4.
3·CH3OH: 
C69H70B2FeN4O3, monoclinic,
P21/n, a =
17.525(1) Å, b = 19.150(2) Å, c =
17.703(1) Å, β = 100.36(1)°, Z = 4.
4-OTf: 
C38H36F6FeN8O6S2,
monoclinic, Pc, a = 10.236(1) Å,
b = 10.129(1) Å, c = 19.251(1) Å,
β = 92.27(1)°, Z =
2. 4-BPh4: 
C84H76B2FeN8,
monoclinic, P21/n, a =
12.489(1) Å, b = 14.189(1) Å, c =
19.843(1) Å, β = 102.84(1)°, Z = 2.