CHEMISTRY OF IRON WITH DIPICOLINIC ACID .3. HEPTACOORDINATED IRON IN [(DIPICH)(2)FE-II(OH2)] AND [(DIPIC)(2)FE-2(II)(OH2)(6)]CENTER-DOT-2DIPICH(2)

Reaction of 2,6-pyridinedicarboxylic acid (dipicolinic acid, dipicH(2)) with Mohr's salt at pH 5.65 afforded [(dipic)(10)(dipicH)(6)Fe-13(II)(OH2)24]. 13H(2)O, which slowly decomposed to a heptacoordinated mononuclear complex (1): [(dipicH)(2)Fe-II(OH2)]. Acidification of [(dipic)(2)Fe-II]Na-2 . 2H(2)O yielded [(dipic)2(dipicH(2))(2)Fe-3(II)(OH2)4], which decomposed to afford the heptacoordinated dinuclear complex [(diPiC)(2)Fe-2(II)(OH2)(6)]. 2dipicH(2) (2). 1p3H(2)O crystallized in the monoclinic space group P2(1)/n with a = 6.996(2) Angstrom, b = 23.898(6) A, c = 10.728(3) Angstrom, beta = 100.25(5)degrees, V = 1765(4) Angstrom(3) and Z = 4. 2 crystallized in the monoclinic space group P2(1)/c with a 9.095(6) Angstrom, b = 14.50(1) Angstrom, c = 12.16(3) Angstrom, beta = 97,28(4)degrees, V = 1598(4) Angstrom(3), and Z = 2. Analysis of the thermal variation of the magnetic susceptibility of 2 indicates the presence of weak antiferromagnetic interactions (J = -3.4 cm(-1), H = -2JS(1)S(2)) of the same order of magnitude as the single-ion zero-field splitting of heptacoordinated iron(II) (-3.1 cm(-1)) in this dinuclear complex.