Synthesis of Oxalato‐Bridged (Oxo)vanadium(IV) Dimers Using L‐Ascorbic Acid as Oxalate Precursor: Structure and Magnetism of Two Systems

Abstract

The reaction of an aqueous solution of NH4VO3 with L‐ascorbic acid and Et4NBr has afforded [Et4N]2[(VO)2(C2O4)3‐(H2O)2]·4H2O (3). A similar reaction, in which malonic acid is also added, has furnished [Et4N]2[(VO)2(C2O4)(C3H2O4)2(H2O)2]·2H2O (4). In these syntheses the oxalate ion is derived from L‐ascorbic acid. In both the complexes the dinuclear anion is centrosymmetric. In 3 the metal atoms are displaced from the plane of the bridging oxalate anion by 0.05 Å, the corresponding displacement in 4 being 0.17 Å. The terminal oxalato chelate ring in 3 is roughly planar but the malonato chelate ring in 4 has a distorted boat conformation. The V−O distances in 4 are systematically shorter than the corresponding distances in 3 by 0.02−0.06 Å. The V···V distance within the dimer is 5.616(2) Å in 3 and 5.529(2) Å in 4. The two uncoordinated water molecules in the asymmetric unit of 3 constitute a hydrogen‐bonded dimer and the lattice consists of a supramolecular anionic assembly held by five different types of O···O hydrogen bonds. The anionic assembly in 4 involves three types of O···O hydrogen bonds. The Et4N+ cations reside between the anionic layers. The magnetic susceptibility data of both 3 and 4 fit excellently with the Heisenberg dimer model in the temperature interval 2−300 K. The species are antiferromagnetic and the J values are −6.50 cm−1 for 3 and −6.25 cm−1 for 4. The two opposing factors — V−O(bridge) bond length and the displacement of the metal atom from the oxalate plane — appear to have more or less balanced each other resulting in virtually equal J values for the two complexes. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

Impairment of ascorbic acid’s anti-oxidant properties in confined media: Inter and intramolecular reactions with air and vanadate at acidic pH

“…In aqueous studies, ascorbate radical formation near neutral and in basic solutions was reported. Prolonged storing of ascorbic acid solutions in the presence of oxygen result in formation of oxalate [91]. Oxalate formation required reaction times of at least two weeks and no oxalic acid was observed in the work presented here.…”

Synthesis, Structure, and Magnetic Properties of Hydroxo‐Bridged Vanadium Oxalate V2O2(OH)2(C2O4)(H2O)2

“…[27] 1.93 ± 0.01 -6.50 ± 0.05 0.01 ± 0.002 0.0018 ± 0.00005 3 [27] 1.95 ± 0.01 -6.25 ± 0.05 0.02 ± 0.002 -0.0004 ± 0.00005 4 [18] 1.91 -3.85 0.008 5 [16] 1 Crystallographic Studies: Intensity data were collected on a Rigaku AFC6S diffractometer with graphite-monochromated Mo-K α (λ = 0.71073 Å) radiation by using the ω-2θ scan method at room temperature. The structure was solved with direct methods and refined on F 2 with full-matrix least-squares methods using SHELXS-97 and SHELXL-97 programs, respectively.…”

“…The V 2 O 10 dimer connected by a common edge found in this compound induces a stronger antiferromagnetic coupling than the oxalato-bridged (oxo)vanadium(IV) dimer. [27] Experimental Section Materials and Analyses: All reagents were of analytical grade and were used as obtained from commercial sources without further purification. IR spectra were recorded in the 400-4000 cm - 0 g, 162 mmol), and deionized H 2 O (15 mL, 0.83 mol) with a mol ratio of about 1.0:14:29:151 was placed in a 50-mL Teflonlined stainless steel autoclave, and the autoclave was sealed, heated to 155°C under autogenous pressure for 20 d, and then cooled to room temperature at a rate of 5°C/h.…”

Synthesis and crystal structure of a Cu(II) complex with mixed malonate/1,10-phenanthroline ligands

“…Selected bond lengths and angles for [Cu 3 (mal) 3 (phen) 3 , the most interesting feature is that there exists an additional [Cu(mal)(phen)] unit (Cu2 unit) between the Cu1 and Cu3 units. In this Cu2 unit, the Cu is coordinated by two O atoms (O6, O9) from different carboxylate groups and two N atoms (N3, N4) from a 1,10-phenanthroline ligand, forming a four-coordinate, square-planar geometry (mean Cu2-N 2.001 and Cu2-O 1.912 Å ).…”

“…In numerous complexes, the malonate dianion generally exhibits bidentate [1][2][3], tridentate [4][5] …”