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

1998-01-26T00:00:00Z (GMT) by Alain Diebold Karl S. Hagen
The synthetic system of Fe(SO<sub>3</sub>CF<sub>3</sub>)<sub>2</sub> 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)(CH<sub>3</sub>CN)<sub>2</sub>](SO<sub>3</sub>CF<sub>3</sub>)<sub>2</sub> (<b>1</b>-OTf) complex forms in acetonitrile, but the high-spin complex Fe(TPA)(SO<sub>3</sub>CF<sub>3</sub>)<sub>2</sub> (<b>2</b>) forms in chloroform. The methanol-bound complex [Fe(TPA)(CH<sub>3</sub>OH)<sub>2</sub>](BPh<sub>4</sub>)<sub>2</sub> (<b>3</b>) forms in the presence of the noncoordinating anion, BPh<sub>4</sub><sup>-</sup>, and six-coordinate [Fe(TPA)<sub>2</sub>](SO<sub>3</sub>CF<sub>3</sub>)<sub>2</sub> (<b>4</b>-OTf) and eight-coordinate [Fe(TPA)<sub>2</sub>](BPh<sub>4</sub>)<sub>2</sub> (<b>4</b>-BPh<sub>4</sub>) 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. <b>1</b>-OTf·CH<sub>3</sub>CN:  C<sub>26</sub>H<sub>27</sub>F<sub>6</sub>FeN<sub>7</sub>O<sub>6</sub>S<sub>2</sub>, monoclinic, <i>P</i>2<sub>1</sub>/<i>n</i>,<i> a</i> = 12.418(2) Å, <i>b</i> = 16.192(4) Å, <i>c</i> = 15.855(2) Å, β = 92.09(2)°, <i>Z</i> = 4. <b>2</b>:  C<sub>20</sub>H<sub>18</sub>F<sub>6</sub>FeN<sub>4</sub>O<sub>6</sub>S<sub>2</sub>, monoclinic, <i>P</i>2<sub>1</sub>/<i>c</i>,<i> a</i> = 17.636(2) Å, <i>b</i> = 9.659(1) Å, <i>c</i> = 16.004(2) Å, β = 113.29 (1)°, <i>Z</i> = 4. <b>3</b>·CH<sub>3</sub>OH:  C<sub>69</sub>H<sub>70</sub>B<sub>2</sub>FeN<sub>4</sub>O<sub>3</sub>, monoclinic, <i>P</i>2<sub>1</sub>/<i>n</i>,<i> a</i> = 17.525(1) Å, <i>b</i> = 19.150(2) Å, <i>c</i> = 17.703(1) Å, β = 100.36(1)°, <i>Z</i> = 4. <b>4</b>-OTf:  C<sub>38</sub>H<sub>36</sub>F<sub>6</sub>FeN<sub>8</sub>O<sub>6</sub>S<sub>2</sub>, monoclinic, <i>Pc</i>,<i> a</i> = 10.236(1) Å, <i>b</i> = 10.129(1) Å, <i>c</i> = 19.251(1) Å, β = 92.27(1)°, <i>Z</i> = 2. <b>4</b>-BPh<sub>4</sub>:  C<sub>84</sub>H<sub>76</sub>B<sub>2</sub>FeN<sub>8</sub>, monoclinic, <i>P</i>2<sub>1</sub>/<i>n</i>,<i> a</i> = 12.489(1) Å, <i>b</i> = 14.189(1) Å, <i>c</i> = 19.843(1) Å, β = 102.84(1)°, <i>Z</i> = 2.