                   _____________________________________________ Corresponding author:  katerinagabriel@yahoo.gr         !"###$! %  &  ’ ( ! ) * + ! ( ,   *            !  "#  "$ %  &   ## ’ $ ( )$  *+ - ./ ( ,/**0  ,1 2 ,/** 33333333333333333333333333333333333333333333333333333333333333333333333333333333333333  In an attempt to understand the aqueous interactions of Cr(III) with the low molecular mass physiological ligand citric acid, the pH"specific synthesis in the binary Cr(III)"citrate system was pursued, leading to the new complexes Na 3 [Cr(C 6 H 5 O 7 ) 2 ]·8.5H 2 O (*) and (Hdmphem) 6 [Cr(C 6 H 5 O 7 ) 2 ] . (NO 3 ) 3 . 14H 2 O (,). Complexes * and , were characterized by elemental analysis, spectroscopic, structural, thermal, EPR and magnetic susceptibility studies. The structures of * and , reveal a mononuclear octahedral complex of Cr(III) with two citrate ligands bound to it. Albeit of the same deprotonation state, the disposition of the two citrate ligands with respect to Cr(III) differs between * and , in the solid state, thus reflecting the presence of pH"structural variants in the requisite binary system. This conformational difference is lifted in aqueous solution, thus providing a) comparative information on the distribution and diversity of species in the binary Cr(III)"citrate system, and b) insight into the nature of interactions developing in the binary Cr(III)"hydroxycarboxylate systems in abiotic and biological applications. : Chromium, synthesis, X"ray structure, Cr(III)"citrate interactions, pH"structural variants, magnetic susceptibility 33333333333333333333333333333333333333333333333333333333333333333333333333333333333333 * # Chromium is a hard, brittle, white metal of the first transition metal series, with physical properties [1] rendering it ideal for industrial applications. The resistance of chromium to attack by a variety of chemicals at normal temperature makes it useful as a protective agent of other more reactive metals, i.e. as a component of stainless steel [2]. However, at high temperatures it reacts with many chemicals. As a typical transition metal element, chromium forms many compounds that are colored and paramagnetic [3]. Its oxidation states vary from "1 to +6, with the most common oxidation states being +2, +3, and +6 [4]. Since Cr(II) is a very strong reducing agent, it is not found in biological systems [5]. All Cr(VI) compounds, except the hexafluoride (CrF 6 ), are oxo compounds; chromium occurs predominantly as either chromate (CrO 4 2" ) or dichromate (Cr 2 O 7 2" ) [6]. In the environment, Cr(VI) is highly water soluble, carcinogenic and mutagenic [7,8]. Cr(VI) compounds are strong oxidizing agents and are therefore readily reduced to Cr(III) in acidic solutions. Cr(III) has been shown to be less harmful in aquatic environments and it readily forms insoluble chromium hydroxides at neutral pH, thus facilitating its removal from the environment [9].