Three tridentate ligands H(2)PhL (Ar = Ph), H(2)ToL (Ar = p-tolyl), and H(2)NpL (Ar = alpha-naphthyl) of structural type HON=C(Ar)N=NC6H4CO2H have been synthesized. These (general abbreviation H(2)ArL) react with iron(III) chloride, affording the pink Et(4)N[Fe(ArL)(2)] (s = 1/2; mu(eff) = 1.98-2.04 mu(B)) in which azo oxime chelation ensures spin-pairing while carboxylate coordination stabilizes the trivalent state. The EPR spectra of the complexes in frozen dimethylformamide-toluene glass (77 K) are rhombic with g values in the range 1.997-2.173. The X-ray structure of Et(4)N[Fe(NpL)(2)]. H2O . CH2Cl2 has been determined, revealing meridional binding of the two ligands affording cis-FeN4O2 geometry. The effect of spin-pairing is expressed in the relatively short (similar to 1.90 Angstrom) Fe-O and Fe-N lengths. The water of crystallization is hydrogen-bonded to carboxyl O atoms. The iron(III)-iron(II) reduction potentials lie near -0.1 V vs SCE. Crystal data for Et(4)N[Fe(NpL)(2)]. H2O . CH2Cl2 : crystal system triclinic, space group , a = 11.539(9) Angstrom, b = 13.306(13) Angstrom, c = 14.60(2) Angstrom, alpha = 89.30(9)degrees, beta = 82.65(9)degrees, gamma = 79.90(8)degrees, V = 2189(4) Angstrom(3), Z = 2, R = 6.59%, R(w) = 6.23%.