Transition metal oxalate complex

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Transition metal oxalate complexes are coordination complexes with oxalate (C2O42−) ligands. Some are useful commercially, but the topic has attracted regular scholarly scrutiny. Oxalate (C2O42-) is a kind of dicarboxylate ligand. [1] As a small, symmetrical dinegative ion, oxalate commonly forms five-membered MO2C2 chelate rings. Mixed ligand complexes are known, e.g., [Co(C2O4)(NH3)4]κ+. [2]

Contents

Homoleptic complexes

Homoleptic oxalato complexes are common, e.g., those with the formula [M(κ2-C2O4)3]n-: M = V(III), Mn(III), [3] Cr(III), Tc(IV), Fe(III), Ru(III), Co(III), Rh(III), Ir(III). These anions are chiral (D3 symmetry), and some have been resolved into their component enantiomers. [4] Some early metals form tetrakis complexes of the type [M(κ2-C2O4)4]n- M = Nb(V), [5] Zr(IV), [6] Hf(IV), [7] Ta(V), [8]

Bimetallic complexes

Oxalate is often a bridging ligand forming bi- and polynuclear complexes with (κ2,κ'2-C2O4)M2 cores. Illustrative binuclear complexes are [M2(C2O4)5]2- M = Fe(II) [9] and Cr(III) [10]

Photochemistry

Potassium ferrioxalate crystals. Potassium ferrioxalate large crystals.jpg
Potassium ferrioxalate crystals.

Metal oxalate complexes are photoactive, degrading with loss of carbon dioxide. This reaction is the basis of the technique called actinometry. UV-irradiation of Pt(C2O4)(PPh3)2 gives derivatives of Pt0(PPh3)2.

See also

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3
[Fe(C
2
O
4
)
3
]. It often occurs as the trihydrate K3[Fe(C2O4)3]·3H2O. Both are crystalline compounds, lime green in colour.

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<span class="mw-page-title-main">Hydrogenoxalate</span> Ion

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2
O
4
or HO
2
C–CO
2
, derived from oxalic acid by the loss of a single proton; or, alternatively, from the oxalate anion C
2
O2−
4
by addition of a proton. The name is also used for any salt containing this anion. Especially in older literature, hydrogenoxalates may also be referred to as bioxalates, acid oxalates, or monobasic oxalates. Hydrogenoxalate is amphoteric, in that it can react both as an acid or a base.

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3
COCHCOCH
3
) and metal ions, usually transition metals. The bidentate ligand acetylacetonate is often abbreviated acac. Typically both oxygen atoms bind to the metal to form a six-membered chelate ring. The simplest complexes have the formula M(acac)3 and M(acac)2. Mixed-ligand complexes, e.g. VO(acac)2, are also numerous. Variations of acetylacetonate have also been developed with myriad substituents in place of methyl (RCOCHCOR′). Many such complexes are soluble in organic solvents, in contrast to the related metal halides. Because of these properties, acac complexes are sometimes used as catalyst precursors and reagents. Applications include their use as NMR "shift reagents" and as catalysts for organic synthesis, and precursors to industrial hydroformylation catalysts. C
5
H
7
O
2
in some cases also binds to metals through the central carbon atom; this bonding mode is more common for the third-row transition metals such as platinum(II) and iridium(III).

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References

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  7. Tranqui, D.; Boyer, P.; Laugier, J.; Vulliet, P. (1977). "Structure cristalline du tétrakisoxalatohafniate de Potassium Pentahydraté [K4Hf(C2O4)4.5H2O]". Acta Crystallographica Section B. 33 (10): 3126–3133. doi:10.1107/S0567740877010395.
  8. Perić, Berislav; Brničević, Nevenka; Jurić, Marijana; Planinić, Pavica; Matković-Čalogović, Dubravka (2009). "[NH4][(CH3)2NH2]2[Ta(C2O4)4]·2H2O: The First (Oxalato)tantalate(V) Complex Structurally Characterized". Structural Chemistry. 20 (5): 933–941. doi:10.1007/s11224-009-9494-0. S2CID   96838371.
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  10. Masters, Vanessa M.; Sharrad, Clint A.; Bernhardt, Paul V.; Gahan, Lawrence R.; Moubaraki, Boujemaa; Murray, Keith S. (1998). "Synthesis, Structure and Magnetism of the Oxalato-Bridged Chromium(III) Complex [NBun4]4[Cr2(ox)5]·2CHCl3". Journal of the Chemical Society, Dalton Transactions (3): 413–416. doi:10.1039/a705265k.