
%0 Journal Article
%A Sugiyarto, Kristian H. 
%A Scudder, Marcia L. 
%A Craig, Donald C. 
%A Goodwin, Harold A. 
%T Electronic and Structural Properties of the Spin Crossover Systems Bis(2,6-bis(pyrazol-3-yl)pyridine)iron(II) Thiocyanate and Selenocyanate
%J Australian Journal of Chemistry
%D 2000/12/22
%V 53
%N 9
%P 755-765
%K Iron(II); thiocyanate; selenocyanate; spin transition; X-ray crystal structure.
%R https://doi.org/10.1071/CH00087
%U https://www.publish.csiro.au/paper/CH00087 
%X Essentially high-spin &#91;Fe(bpp)2&#93;&#91;NCS&#93;2&#183;2H2O and &#91;Fe(bpp)2&#93;&#91;NCSe&#93;2 (bpp = 2,6-bis(pyrazol-3-yl)pyridine) were isolated from an aqueous reaction mixture. Both salts undergo an abrupt transition to low spin below room temperature, that for the thiocyanate occurring in two steps and the high-spin &AElig; low-spin &AElig; high-spin cycle being accompanied by hysteresis in both steps. Recrystallization of the salts from nitromethane yielded a mixture from which bright yellow crystals were separated for structure determination. In addition, from the recrystallized selenocyanate, deep red-brown crystals of composition &#91;Fe(bpp)2&#93;&#91;NCSe&#93;2&#183;H2O&#183;0.25 CH3NO2 were obtained. Recrystallized &#91;Fe(bpp)2&#93;&#91;NCS&#93;2&#183;2H2O and &#91;Fe(bpp)2&#93;&#91;NCSe&#93;2 were identified as high spin with average Fe&#8211;N distances of 2.16 and 2.17 &#197;, respectively. In the unit cell of &#91;Fe(bpp)2&#93;&#91;NCSe&#93;2&#183;H2O&#183;0.25 CH3NO2, there are four independent iron atoms, three identified as low spin and the fourth as high spin. All salts crystallize in a layer-type array involving edge-to-face and face-to-face aryl&#8211;aryl-type interactions. Hydrogen bonding between pyrazole &#62;NH groups, anions and solvate molecules is observed. The structure of the uncoordinated ligand was also determined, the molecule being found in a planar arrangement with thecis&#8211;cis configuration for the pyrazolyl groups relative to the central pyridyl and the &#62;NH group being at the N 2 atom. Hydrogen bonding involving the &#62;NH groups leads to stepped stacks of molecules. The principal difference in the geometry of coordinated and free bpp molecules is a contraction in the angles about the interannular bridges in the chelate rings. &#91;Fe(bpp)2&#93;&#91;NCS&#93;2&#183;2H2O: triclinic, space group P1&#8211;, a 8.302(6), b 8.446(6), c 21.531(13) &#197;, a 78.78(5), b 82.80(5), g 89.85(4)&#x02DA;, Z 2. &#91;Fe(bpp)2&#93;&#91;NCSe&#93;2: triclinic, space group P1&#8211;, a 8.354(4), b 8.409(4), c 19.918(9) &#197;, a 87.02(3), b 83.15(3), g 88.86(3)&#x02DA;, Z 2. &#91;Fe(bpp)2&#93;&#91;NCSe&#93;2&#183;H2O&#183;0.25 CH3NO2: monoclinic, space group Pn, a 16.425(12), b 20.774(9), c 16.933(14) &#197;, b 90.91(4)&#x02DA;, Z 8. Uncoordinated bpp: orthorhombic, space group Pna21, a 8.075(3), b 22.479(9), c 5.525(1) &#197;, b Z 4. 
