SYNTHESIS OF PYRROLOQUINOLINEQUINONE ANALOGS - MOLECULAR-STRUCTURE AND MOSSBAUER AND MAGNETIC-PROPERTIES OF THEIR IRON COMPLEXES

Four complexes. Fe-II(L(2))(2) (1), [Fe-II(L(2))(Cl)(MeOH)(2)](2) (2), Fe-II(L(3)H(2))(2) (3), and Fe-III(L(4))(2)Cl.2(Et(3)N.HCl).0.5CH(3)CN (4), wherein L(2)H, L(3)H(3), and L(4)H are analogs of pyrroloquinolinequinone or methoxatin (PQQ). have been synthesized and studied. 2 crystallizes in the triclinic system, space group P $($) over bar$$ 1, Z = 2, a = 9.588(6) Angstrom, b = 10.011(7) Angstrom, c = 11.770(5) Angstrom, alpha = 96.66(5)degrees, beta = 99.21(5)degrees, and gamma = 107.93(7)degrees. The structure was solved by direct methods and refined to conventional agreement indices R = 0.054 and R(w) = 0.063 with 2683 unique reflections for which I > 3 sigma(I). The molecular structure of 2 consists of discrete [Fe-II(L(2))(Cl)(MeOH)(2)] molecules associated into dimeric units through the carboxylate function of L(2). The carboxylate oxygen atoms of the two molecules constituting the dimeric unit bridge the metal centers affording a Fe...Fe' separation of 3.645(4) Angstrom. The distorted coordination octahedron around each Fe(II) includes the pyridine nitrogen and carboxylate oxygen atoms of L(2), the chloride anion. and the oxygen atom of two methanol molecules. The synthesis and IR, Mossbauer, and magnetic susceptibility studies of 1-4 evidence the variety of structural types and nuclearities obtained for iron complexes of PQQ analogs, depending upon the stoichiometry and pH of the reactions, Complexes 1 and 3 (mononuclear) and 4 (polynuclear) are characterized by the 1:2 Fe:L ratio while complex 2 (dimer) is characterized by the 1:1 Fe:L ratio. Among the analogs used in this study, those of the reduced form of PQQ chelate iron through their tridentate site while chelation occurs preferentially at the quinonic site far the analog of the oxidized form of PQQ.