chemistry

Transition metal carboxylate complex

Transition metal carboxylate complex is a chemistry topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Transition metal carboxylate complex rather than just read about it. In short: Transition metal carboxylate complexes are coordination complexes with carboxylate (RCO−2) ligands. Reflecting the diversity of carboxylic acids, the inventory of metal carboxylates is large.

Key takeaways

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Reference excerpt

Transition metal carboxylate complexes are coordination complexes with carboxylate (RCO−2) ligands. Reflecting the diversity of carboxylic acids, the inventory of metal carboxylates is large. Many are useful commercially, and many have attracted intense scholarly scrutiny. Carboxylates exhibit a variety of coordination modes, most common are κ1 (O-monodentate), κ2 (O,O-bidentate), and bridging.

Acetate and related monocarboxylates

Structure and bonding Carboxylates bind to single metals by one or both oxygen atoms, the respective notation being κ1- and κ2-. In terms of electron counting, κ1-carboxylates are "X"-type ligands, i.e., a pseudohalide-like. κ2-carboxylates are "LX ligands", i.e. resembling the combination of a Lewis base (L) and a pseudohalide (X). Carboxylates are classified as hard ligands, in HSAB theory.

For simple carboxylates, the acetate complexes are illustrative. Most transition metal acetates are mixed ligand complexes. One common example is hydrated nickel acetate, Ni(O2CCH3)2(H2O)4, which features intramolecular hydrogen-bonding between the uncoordinated oxygens and the protons of aquo ligands. Stoichiometrically simple complexes are often multimetallic. One family are the basic metal acetates, of the stoichiometry [M3O(OAc)6(H2O)3]n+.

Homoleptic complexes Homoleptic carboxylate complexes are usually coordination polymers. But exceptions exist.

A molecular monocarboxylate is silver acetate, Ag2(OAc)2. Molecular diacetates are more common. Several diacetates adopt the Chinese lantern structure. Well studied examples include the dimetal tetraacetates (M2(OAc)4) including rhodium(II) acetate, copper(II) acetate, molybdenum(II) acetate, and chromium(II) acetate. Platinum diacetate and palladium diacetate feature Pt4 and Pd3 cores, further illustrating the tendency of acetate ligands to stabilize multimetallic structures. Mononuclear tricarboxylates include derivatives of 1-adamantanecarboxylic acid, which have the formula [M(O2CC10H11)3]− (M = Co, Ni, Zn). The carboxylates are bidentate.

Synthesis Many methods allow the synthesis of metal carboxylates. From preformed carboxylic acid, the following routes have been demonstrated:

acid-base reactions: LnMOR′ + RCO2H → LnMO2CR + R′OH protonolysis: LnM(alkyl) + RCO2H → LnMO2CR + alkane oxidative addition: LnM + RCO2H → Ln(H)MO2CR From preformed carboxylate, salt metathesis reactions are common:

LnMCl + RCO2Na → LnMO2CR + NaCl Some metal oxides react with acetic anhydride to give carboxylates, Examples include chromyl acetate (CrO2(O2CCH3)2) and vanadyl acetate (VO(O2CCH3)2). Metal carboxylates can be prepared by carboxylation of highly basic metal alkyls:

LnMR + CO2 → LnMO2CR

Reactions A common reaction of metal carboxylates is their displacement by more basic ligands. Acetate is a common leaving group. They are especially prone to protonolysis, which is widely used to introduce ligands, displacing the carboxylic acid. In this way octachlorodimolybdate is produced from dimolybdenum tetraacetate:

Mo2(O2CCH3)4 + 4 HCl + 4 KCl → K4[Mo2Cl8] + 4 CH3CO2H Acetates of electrophilic metals are proposed to function as bases in concerted metalation deprotonation reactions. Attempts to prepare some carboxylate complexes, especially for electrophilic metals, often gives oxo derivatives. Examples include the oxo-acetates of Fe(III), Mn(III), and Cr(III). Pyrolysis of metal carboxylates affords acid anhydrides and the metal oxide. This reaction explains the formation of basic zinc acetate from anhydrous zinc diacetate. In some cases, monodentate carboxylates undergo O-alkylation to give esters. Strong alkylating agents are required.

Other carboxylates Many carboxylates form complexes with transition metals. Alkyl and simple aryl carboxylates behave similarly to the acetates. Trifluoroacetates differ in mononuclear complexes because it is usually monodentate, for example [Zn(κ2-O2CCH3)2(OH2)2] versus [Zn(κ1-O2CCF3)2(OH2)4].

Applications

Metal naphthenates and ethylhexanoates

Naphthenic acids, mixtures of long chain and cyclic carboxylic acids extracted from petroleum, form lipophilic complexes (often called salts) with transition metals. These metal naphthenates have the formula M(naphthenate)2, or M3O(naphthenate)6, have diverse applications including synthetic detergents, lubricants, corrosion inhibitors, fuel and lubricating oil additives, wood preservatives, insecticides, fungicides, acaricides, wetting agents, thickening agent, and oil drying agents. Industrially useful naphthenates include those of aluminium, magnesium, calcium, barium, cobalt, copper, lead, manganese, nickel, vanadium, and zinc. Illustrative is the use of cobalt naphthenate for the oxidation of tetrahydronaphthalene to the hydroperoxide.

Like naphthenic acid, 2-ethylhexanoic acid forms lipophilic complexes that are used in organic and industrial chemical synthesis. They function as catalysts in polymerizations as well as for oxidation reactions as oil drying agents. Metal ethylhexanoates are referred to as metallic soaps.

Aminopolycarboxylates

A commercially important family of metal carboxylates is derived from aminopolycarboxylates such as EDTA4−. Related to these synthetic chelating agents are the amino acids, which form large families of amino acid complexes. Two amino acids, glutamate and aspartate, have carboxylate side chains, which function as ligands for iron in nonheme iron proteins, such as hemerythrin.

Metal organic frameworks (MOFs) Metal organic frameworks, porous, three-dimensional coordination polymers, are often derived from metal carboxylate clusters. These clusters, called secondary bonding units (SBUs), are often linked by the conjugate bases of benzenedi- and -tricarboxylic acids.

Reagents for organic synthesis

It has been claimed that "cobalt carboxylates are the most widely used homogeneous catalysts in industry" as they are used in the oxidation of p-xylene to terephthalic acid. Palladium(II) acetate has been described as being "among the most extensively used transition metal complexes in metal-mediated organic synthesis". Many coupling reactions utilize this reagent, which is soluble in organic solvents and which contains a built-in Bronsted base (acetate). Dirhodium tetrakis(trifluoroacetate) is widely used catalyst for reactions involving diazo compounds.

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Illustrations

Worked examples

Example 1 — a first encounter with Transition metal carboxylate complex

Start with the simplest possible case. Write down what Transition metal carboxylate complex claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In chemistry, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Transition metal carboxylate complex before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Transition metal carboxylate complex ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Transition metal carboxylate complex

In research: Transition metal carboxylate complex appears in chemistry research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Transition metal carboxylate complex in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Transition metal carboxylate complex is common in secondary-school and first-year university syllabi. It links to neighbouring topics Coordination complexes, Ligands, Salts of carboxylic acids, so understanding it makes those chapters shorter.
In everyday life: Look for Transition metal carboxylate complex outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Transition metal carboxylate complex in 20 minutes

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Frequently asked questions

What is Transition metal carboxylate complex in simple terms?

Transition metal carboxylate complexes are coordination complexes with carboxylate (RCO−2) ligands. Reflecting the diversity of carboxylic acids, the inventory of metal carboxylates is large.

Why does Transition metal carboxylate complex matter?

Because it connects several chemistry ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Transition metal carboxylate complex?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Transition metal carboxylate complex.