CHEMISTRY OF IRON WITH DIPICOLINIC ACID .2. BRIDGING ROLE OF CARBOXYLATE GROUPS IN SOLID-STATE STRUCTURES

This paper reports the syntheses, structures, and properties of iron(I I) and dipicolinic acid oligonuclear complexes prepared in slightly ac idic medium. Acidification of [(dipic)(2)Fe-II]Na-2 . 2H(2)O or reacti on of dipicH(2) (2,6-pyridine dicarboxylic acid) and Mohr's salt (ammo nium iron(II) sulfate hexahydrate) at pH 5.3 yielded [(dipic)(2)(dipic H)(2)Fe(II)3(OH2)4].2H2O (1), which consists of two [(dipic)(dipicH)Fe -II] fragments sharing one oxygen atom each with a [Fe-II(OH2)(4)O-2] subunit. Reaction of dipicH(2) and Mohr's salt at pH 6.25 gave the din uclear species [(dipic)(2)Fe(II)2(OH2)(5)] (2), in which a [(dipic)(2) Fe-II] moiety shares one oxygen atom with a [Fe-II(OH2)(5)O] fragment. When the reaction was conducted at pH 5.85, the reaction gave crystal s of [(dipic)(4)(dipicH(2))(2)Fe(II)3(OH2)(6)](NH4)(2) . 4H(2)O (3), w hich contains, in the unit cell, both the reactants [Fe-II(OH2)(6)](2) and dipicH(2) and the product [(dipic)(2)Fe-II](2-). At pH 5.65, the reaction yielded crystals of [(dipic)(10)(dipicH)(6)Fe-13(II)(OH2)(24 )]. 13H(2)O (4), which contains, in the same unit cell, one trinuclear anionic complex )(2)Fe-II]-[Fe-II(OH2)(4)]-[Fe-II(dipic)(2)]}(2-), tw o doubly protonated cationic dinuclear complexes {[(dipicH)Fe-II(dipic H)]-[Fe-II(OH2)(5)]}(2+), two singly protonated cationic dinuclear com plexes [(dipicH)Fe-II(dipic)]-[Fe-II(OH2)(5)](+), and two mononuclear anionic complexes [(dipic)(2)Fe-II](2-). The crystal structures for 1- 4 have been solved: 1 crystallized in the monoclinic space group P2(1) /n with a = 8.956(3) Angstrom, b = 15.083(7) Angstrom Angstrom, c = 12 .504(5) Angstrom, beta = 90.42(8)degrees, V = 1689(1) Angstrom(3), and Z = 2. 2 was found in the triclinic space group P (1) over bar with a = 8.339(2) Angstrom, b = 9.711(2) Angstrom, c = 13.994(4) Angstrom, a lpha = 100.75((4)degrees, beta = 101.99(2)degrees, gamma = 97.04(2)deg rees, V = 1076(13) Angstrom(3), and Z = 2. 3 crystallized in the tricl inic space group P (1) over bar with a = 10.759(2) Angstrom, b = 10.91 7(3) Angstrom, c = 12.653(3) Angstrom, alpha = 105.62(2)degrees, beta = 96.25(2)degrees, gamma 103.25(2)degrees, V = 1370(11) Angstrom(3), a nd Z = 1.4 was found in the triclinic space group P (1) over bar with a = 15.700(4) Angstrom, b = 15.811(4) Angstrom, c = 16.558(5) Angstrom , alpha = 85.49(2)degrees, beta = 67.75(2)degrees, gamma = 76.47(3)deg rees, V = 3698(15) Angstrom(3), and Z = 1.