chemistry

Metal–metal bond

Metal–metal bond 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 Metal–metal bond rather than just read about it. In short: In inorganic chemistry, metal–metal bonds describe attractive interactions between metal centers. The simplest examples are found in bimetallic complexes.

Key takeaways

Metal–metal bond belongs to chemistry; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Metal–metal bond to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Metal–metal bond from memory before moving on to harder problems.

Reference excerpt

In inorganic chemistry, metal–metal bonds describe attractive interactions between metal centers. The simplest examples are found in bimetallic complexes. Metal–metal bonds can be "supported", i.e. be accompanied by one or more bridging ligands, or "unsupported". They can also vary according to bond order. The topic of metal–metal bonding is usually discussed within the framework of coordination chemistry, but the topic is related to extended metallic bonding, which describes interactions between metals in extended solids such as bulk metals and metal subhalides.

Unsupported metal–metal bonds An example of a metal–metal bond is found in dimanganese decacarbonyl, Mn2(CO)10. As confirmed by X-ray crystallography, a pair of Mn(CO)5 units are linked by a bond between the Mn atoms. The Mn-Mn distance (290 pm) is short. Mn2(CO)10 is a simple and clear case of a metal-metal bond because no other atoms tie the two Mn atoms together. When several metals are linked by metal-metal bonds, the compound or ion is called a metal cluster. Many metal clusters contain several unsupported M–M bonds. Some examples are M3(CO)12 (M = Ru, Os) and Ir4(CO)12. A subclass of unsupported metal–metal bonded arrays are linear chain compounds. In such cases the M–M bonding is weak as signaled by longer M–M bonds and the tendency of such compounds to dissociate in solution.

Supported metal–metal bonds In many compounds, metal-metal bonds are accompanied by bridging ligands. In those cases, it is difficult to state unequivocably that the metal-metal bond is the cohesive force binding the two metals together. Diiron nonacarbonyl is such an example. Another example of a supported metal–metal bond is cyclopentadienyliron dicarbonyl dimer, [(C5H5)Fe(CO)2]2. In the predominant isomers of this complex, the two Fe centers are joined not only by an Fe–Fe bond, but also by bridging CO ligands. The related cyclopentadienylruthenium dicarbonyl dimer features an unsupported Ru–Ru bond. Many metal clusters contain several supported M–M bonds. Further examples are Fe3(CO)12 and Co4(CO)12.

Multiple metal–metal bonds

In addition to M–M single bonds, metal pairs can be linked by double, triple, quadruple, and in a few cases, quintuple bonds. Isolable complexes with multiple bonds are most common among the transition metals in the middle of the d-block, such as rhenium, tungsten, technetium, molybdenum and chromium. Typical the coligands are π-donors, not π-acceptors. Well studied examples are the tetraacetates, such as dimolybdenum tetraacetate (quadruple bond) and dirhodium tetraacetate (single bond). Mixed-valence druthenium tetraacetates have fractional M–M bond orders, i.e., 2.5 for [Ru2(OAc)4(H2O)2]+. The complexes Nb2X6(SR2)3 adopt a face-sharing bioctahedral structures (X = Cl, Br; SR2 = thioether). As dimers of Nb(III), they feature double metal–metal bonds, the maximum possible for a pair of metals with d2 configuration. Hexa(tert-butoxy)ditungsten(III) is a well studied example of a complex with a metal–metal triple bond.

References

Illustrations

Worked examples

Example 1 — a first encounter with Metal–metal bond

Start with the simplest possible case. Write down what Metal–metal bond 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 Metal–metal bond 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 Metal–metal bond 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 Metal–metal bond

In research: Metal–metal bond 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 Metal–metal bond 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: Metal–metal bond is common in secondary-school and first-year university syllabi. It links to neighbouring topics Chemical compounds containing metal–metal bonds, Cluster chemistry, so understanding it makes those chapters shorter.
In everyday life: Look for Metal–metal bond 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 Metal–metal bond in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Metal–metal bond means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Metal–metal bond out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Metal–metal bond in simple terms?

In inorganic chemistry, metal–metal bonds describe attractive interactions between metal centers. The simplest examples are found in bimetallic complexes.

Why does Metal–metal bond 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 Metal–metal bond?

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 Metal–metal bond.