Synthesis, Characterization, and Structures of Mn(DMHP)₃·12H₂O and Mn(DMHP)₂Cl·0.5H₂O

Abstract

This report describes the synthesis, characterization, and X-ray crystal structures of two Mn(III) complexes, Mn(DMHP)3 x 12H2O and Mn(DMHP)2Cl x 0.5H2O (DMHP = 1,2-dimethyl-3-hydroxy-4-pyridinone). Mn(DMHP)2Cl was prepared from the reaction of Mn(II) chloride with 2 equiv of DMHP under reflux in the presence of triethylamine. Mn(DMHP)3 was obtained by reacting Mn(II) acetate with 3 equiv of DMHP in the presence of sodium acetate. Mn(DMHP)3 could also be prepared by reacting Mn(OAc)3 x 2H2O with 3 equiv of DMHP in the presence of triethylamine. Both Mn(III) complexes have been characterized by elemental analysis, infrared spectroscopy, electronic paramagnetic resonance, electrospray ionization spectroscopy, electrochemical method, and X-ray crystallography. The X-ray crystal structure of Mn(DMHP)2Cl x 0.5H2O revealed a rare example of five-coordinated Mn(III) complexes with two bidentate ligands and a square pyramidal coordination geometry. Surprisingly, the average Mn-O (hydroxy) bond distance in Mn(DMHP)2Cl x 0.5H2O is approximately 0.025 A longer than that of the average Mn-O (carbonyl) bond, suggesting an extensive delocalization of electrons in the two pyridinone rings. The structure of Mn(DMHP)3 x 12H2O, a rare example of six-coordinate high-spin Mn(III) complexes without Jahn-Teller distortion, is isostructural to M(DMHP)3 x 12H2O (M = Al, Ga, Fe, and In). The electrochemical data for Mn(DMHP)3 suggests that the Mn(III) oxidation state is highly stabilized by three DMHP ligands. DMHP has the potential as a chelator for the removal of excess intracellular Mn and the treatment of chronic Mn toxicity.

Epoxidation of strained alkenes catalysed by (1,2-dimethyl-4(1H)pyridinone-3-olate)2MnIIICl

“…We have not been able to characterise this amorphous residue. Based on the above mentioned MS analysis and previous literature reports on ( 16 while that of (salen)Mn III in acetonitrile was reported to be +1.29 V vs NHE. 30 We can therefore extrapolate that the (DMPO) 2 Mn IV/V redox potential of 1 is also much lower than the one of (salen)Mn IV/V .…”

“…16 Hydrogen peroxide was 30% w/v in water, tBuOOH was 70% in water. Iodosylbenzene and MPPH were prepared by literature methods.…”

“…Cyclic voltammetry of complex 1 was reported in the literature. 16 It was reported that the Mn III /Mn IV couple in 1 has a redox potential (quasi-reversible) of +0.54V vs NHE in acetonitrile. Upon addition of 5 equivalents of imidazole or sodium acetate, that couple is shifted to +0.26 V and +0.33 V respectively (data not shown).…”

Hydroxypyridinone Chelators: From Iron Scavenging to Radiopharmaceuticals for PET Imaging with Gallium-68

“…3,4-HPs have high affinity for both Fe 3+ and Ga 3+ , and form neutral 3:1 bidentate complexes with Fe 3+ and Ga 3+ ( Figure 3 , Table 2 ) (as well as Al 3+ , In 3+ , Cr 3+ , Mn 3+ and Gd 3+ ) [ 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 ]. Both the [Fe(deferiprone) 3 ] [ 31 ] and [Ga(deferiprone) 3 ] [ 29 ] complexes crystallise in the same octahedral geometries with comparable bond lengths and angles.…”

“…Within each deferiprone ligand, bond angles are 80.91° for O 3 –Fe–O 4 , and 83.22° for O 3 –Ga–O 4 . Other metal ions (M = Al 3+ , In 3+ , Cr 3+ , Mn 3+ ) form isostructural [M(deferiprone) 3 ] complexes [ 27 , 28 , 29 , 30 ], and in all cases, fac geometries are observed in the solid state. However, 1 H NMR studies on diamagnetic Ga 3+ and Al 3+ complexes suggest that conversion between fac and mer geometric isomers occurs in solution [ 30 ].…”