Manganese Citrate Chemistry:  Syntheses, Spectroscopic Studies, and Structural Characterizations of Novel Mononuclear, Water-Soluble Manganese Citrate Complexes

Abstract

The first two mononuclear manganese citrate complexes, (NH4)4[MnII(C6H5O7)2] (1) and (NH4)5[MnIII(C6H4O7)2].2H2O (2) were synthesized in aqueous solutions near physiological pH values. They were isolated in their pure crystalline forms and characterized by elemental analyses and spectroscopic techniques, including UV/visible, electron paramagnetic resonance, Fourier transformed infrared, and magnetic susceptibility measurements. Compound 1 crystallizes in the monoclinic space group P2(1)/c, with a = 8.777(1) A, b = 13.656(3) A, c = 9.162(2) A, beta = 113.62(2) degrees, V = 1006.2(6) A3, and Z = 2. Compound 2 crystallizes in the triclinic space group P1, with a = 9.606(3) A, b = 9.914(3) A, c = 7.247(3) A, alpha = 91.05(1) degrees, beta = 105.60(1) degrees, gamma = 119.16(1) degrees, V = 571.3(3) A3, and Z = 1. The X-ray crystal structures of 1 and 2 revealed that, in both cases, the manganese ion is six-coordinate and is bound by two citrate ligands in a distorted octahedral fashion. In the case of complex 1, the citrate ion binds to Mn2+ as a triply deprotonated ligand, retaining the central carbon hydroxyl hydrogen, whereas, in the case of compound 2, the citrate ligand coordinates to Mn3+ as a fully deprotonated entity. Compound 2 contains water molecules of crystallization in the unit cell which, through extensive hydrogen-bonding interactions, bestow considerable stability upon the Mn(3+)-citrate assembly. There are significant contributions to the stabilities of the assembled lattices in 1 and 2 arising from the ammonium counterions neutralizing the high anionic charges of the complexes. The EPR spectra attest to the presence of paramagnetic Mn2+ and Mn3+ species in the solid state. Corroborative evidence is obtained from the magnetic susceptibility measurements in the range 5-300 K. Complexes 1 and 2 present clear cases of mononuclear manganese citrate species relevant to manganese speciation in biological media and potentially related to the beneficial as well as toxic effects of manganese on humans.

New Trends in the Chemistry of Iron(III) Citrate Complexes: Correlations between X‐ray Structures and Solution Species Probed by Electrospray Mass Spectrometry and Kinetics of Iron Uptake from Citrate by Iron Chelators

“…In complexes 6 and 8, the citrate ligand has a non-coordinating carboxylic group (non-deprotonated), whereas the alcohol function is deprotonated. This deprotonation is promoted by Fe III , which is a hard Lewis acid, whereas with Fe II , [23] Mn II , [20] and Co II[24] the alcohol function remains protonated and hence only coordinates in monodentate mode.…”

“…Doing so, the symmetry expansion of two hydrogen atoms linked to this nitrogen would lead to a non-consistent square-planar ammonium cation. In the previously reported structure [12] of 7, and also for the isostructural compounds (NH 4 ) 5 [19,20] the authors suggested that this ammonium cation was disordered. As has been underlined in a study of aluminum and gallium citrate complexes, [19b] the nitrogen and oxygen atoms have almost the same weights in the Fourier map.…”

“…Crystal data for 7 were collected at 170 K, making the resolution of the disorder easier than in previously reported structures [12,19,20] for which the crystal data were collected at room temperature.…”

Synthesis, structure and magnetic properties ofβ-MnO 2 nanorods

“…Hydrothermal synthesis was performed at 100°C for 48 h. The product was filtered and rinsed with ethanol and dried at 100°C for 12 h. The polymer involved in the synthesis was fired out by sintering at 500°C in air for 2 h, which resulted in a black solid as the final product. The role of the polymer in the synthesis and the calcination of the polymeric precursor at high temperature in air are described elsewhere [9], whereas the chemistry of manganese citrate complexes is explained in [10]. Scanning electron-(SEM) and transmission electron (TEM) microscope images of the product material (Fig.…”

Functional Characterization and Metal Ion Specificity of the Metal-Citrate Complex Transporter from Streptomyces coelicolor

“…The two most common citrate-to-metal binding motifs are a linear citrate backbone and a "bent" citrate backbone. The manganese is found with the linear arrangement (24). Iron-citrate structures described by Matzapetakis et al describe the citrate in the "bent" arrangement for Fe 3ϩ (25).…”