CHEMISTRY OF IRON WITH DIPICOLINIC ACID .4. MIXED-LIGAND COMPLEXES OF IRON(III) AND RELATED-COMPOUNDS

The chemistry of iron(III)-2,6-pyridinedicarboxylic (dipicolinic, dipicH(2)) acid complexes with various ligands has been explored. Reaction of [(dipic)Fe-II(OH2)(3)] with bromine water at room temperature led to the binuclear [(dipic)(H2O)Fe-III(mu-OH)(2)Fe-III(OH2)(dipic)] complex in high yield. This dimer reacted with HX to give [(dipic)-(X)Fe-III(OH2)(2)] (X = Br or Cl(1)). Reaction of 1 with 2,4-pentanedione (acacH) yielded [(dipic)(acac)Fe-III-(OH2)] (2), and reaction with 1,10-phenanthroline (phen) gave [(dipic)(Cl)Fe-III(phen)] (3). The reaction of [(dipic)Fe-II(OH2)(3)] with polypyridyl tridentate ligands L did not yield [(dipic)Fe-II(L)] but [Fe(II)L(2)](2+) with [(dipic)(2)Fe-III](-) as counterions. For instance, with L = 2,2':6',2''-terpyridine (tpy), the reaction gave [Fe-II(tpy)(2)][(dipic)(2)-Fe-III](2) (4) and with L = tetrakis(2-pyridyl)pyrazine (tppz) it gave {[Fe-II(tppz)(2)][(dipic)(2)Fe-III](3)}.(H3O) (5) The crystallographic structures of 1-5 have been solved: 1, monoclinic, C2/c, a = 6.015(6) Angstrom, b = 18.74(1) Angstrom, c = 9.81(1) Angstrom, beta = 105.5(6)degrees, V = 1062(2) Angstrom(3), Z = 4; 2 . 0.5C(2)H(5)OH, monoclinic, C2/c, a = 11.510(3) Angstrom, b = 12.734(4) Angstrom, c = 21.819(4) Angstrom, beta = 98.27(2)degrees, V = 3165(7) Angstrom(3), Z = 8; 3 . CH2Cl2, monoclinic, P2(1)/n, a = 9.083-(2) Angstrom, b = 12.899(2) Angstrom, c = 17.490(4) Angstrom, beta = 96.70(8)degrees, V = 2035(2) Angstrom(3), Z = 4; 4 . H2O . 3CH(3)CN, monoclinic, P2(1)/n, a = 8.947(2) Angstrom, b = 37.37(2) Angstrom, c = 18.97(2) Angstrom, beta = 100.07(8)degrees, V = 6243(8) Angstrom(3), Z = 4; 5 . 11H(2)O, monoclinic, C2/c, a = 32.46(3) Angstrom, b = 28.30 Angstrom, c = 27.59(2) Angstrom, beta = 126.34(6)degrees, V = 20417 Angstrom(3) and Z = 8.