science

Transition metal nitrile complexes

Transition metal nitrile complexes is a science 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 nitrile complexes rather than just read about it. In short: Transition metal nitrile complexes are coordination compounds containing nitrile ligands. Because nitriles are weakly basic, the nitrile ligands in these complexes are often labile.

Key takeaways

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Reference excerpt

Transition metal nitrile complexes are coordination compounds containing nitrile ligands. Because nitriles are weakly basic, the nitrile ligands in these complexes are often labile.

Ligand properties

According to the Covalent bond classification method, nitriles are classified as L ligands, i.e., charge-neutral Lewis bases. With respect to HSAB theory, they are classified as soft. Typical nitrile ligands are acetonitrile, propionitrile, and benzonitrile. The structures of [Ru(NH3)5(NCPh)]n+ have been determined for the 2+ and 3+ oxidation states. Upon oxidation the Ru-NH3 distances contract and the Ru-NCPh distances elongate, consistent with amines serving as pure-sigma donor ligands and nitriles functioning as pi-acceptors.

Synthesis and reactions Acetonitrile, propionitrile and benzonitrile are also popular solvents. Because nitrile solvents have high dielectric constants, cationic complexes containing a nitrile ligand are often soluble in a solution of that nitrile. Some complexes can be prepared by dissolving an anhydrous metal salt in the nitrile. In other cases, a suspension of the metal is oxidized with a solution of NOBF4 in the nitrile:

Ni + 6 MeCN + 2 NOBF4 → [Ni(MeCN)6](BF4)2 + 2 NO Heteroleptic complexes of molybdenum and tungsten can by synthesized from their respective hexacarbonyl complexes.

M(CO)6 + 4 MeCN + 2 NOBF4 → [M(NO)2(MeCN)4](BF4)2

For the synthesis of some acetonitrile complexes, the nitrile serves as a reductant. This method is illustrated by the conversion of molybdenum pentachloride to the molybdenum(IV) complex:

2 MoCl5 + 5 CH3CN → 2 MoCl4(CH3CN)2 + ClCH2CN + HCl

Reactions Transition metal nitrile complexes are usually employed because the nitrile ligand is labile and relatively chemically inert. Cationic nitrile complexes are however susceptible to nucleophilic attack at carbon. Consequently some nitrile complexes catalyze the hydrolysis of nitriles to give the amides. Fe- and Co-nitrile complexes are intermediates in nitrile hydratase enzymes. N-coordination activates the sp-hybridized carbon center toward attack by nucleophiles, including water. Thus coordination of the nitrile to a cationic metal center is the basis for the catalytic hydration:

M-NCR + H2O → M-O=C(NH2)R M-O=C(NH2)R + NCR → O=C(NH2)R + M-NCR In a related reaction, alcohols add to nitrile ligands. Nitrile ligands in electron-rich complexes are susceptible to oxidation, e.g. by iodosylbenzene. Nitriles undergo coupling with alkenes, also involving electron-rich complexes.

Examples

[M(NCMe)6]n+ Hexakis(acetonitrile)vanadium(II) tetrachlorozincate ([V(MeCN)6](ZnCl4)), green Hexakis(acetonitrile)chromium(II) bis(tetraphenylborate) ([Cr(MeCN)6](B(C6H5)4)2, green Hexakis(acetonitrile)chromium(III) tetrafluoroborate ([Cr(MeCN)6](BF4)3), white Hexakis(acetonitrile)iron(II) bis(tetrakis(pentafluorophenyl)borate) ([Fe(MeCN)6](B(C6F5)4)2, orange Hexakis(acetonitrile)cobalt(II) bis(tetrakis(pentafluorophenyl)borate) ([Co(MeCN)6](B(C6F5)4)2, purple Hexakis(acetonitrile)nickel(II) tetrafluoroborate ([Ni(MeCN)6](BF4)2), blue Hexakis(acetonitrile)copper(II) bis(tetrakis(pentafluorophenyl)borate) ([Cu(MeCN)6](B(C6F5)4)2, pale blue-green solid Hexakis(acetonitrile)ruthenium(II) tetrafluoroborate ([Ru(MeCN)6](BF4)2), white, dRu-N = 202 pm. Hexakis(acetonitrile)rhodium(III) tetrafluoroborate ([Rh(MeCN)6](BF4)3), a yellow solid. Hexakis(acetonitrile)rhenium(II) tetrafluoroborate ([Re(MeCN)6](BF4)2), a yellow solid. Hexakis(acetonitrile)rhenium(III) tetrafluoroborate ([Re(MeCN)6](BF4)3), a brown solid.

[M(NCMe)4]n+ [Cr(MeCN)4](BF4)2, blue [Cu(MeCN)4]PF6, colorless [Pd(MeCN)4](BF4)2, yellow

[M(NCMe)4 or 5]2n+ [Mo2(MeCN)8/10](BF4)4 blue d(Mo-Mo) = 218, d(Mo-N)axial = 260, d(Mo-N)equat = 214 pm [Tc2(MeCN)10](BF4)4 [Re2(MeCN)10][B(C6H3(CF3)2)4]2, blue; d(Re-Re) = 226, d(Re-N)axial = 240, d(Re-N)equat = 205 pm [Rh2(MeCN)10](BF4)4, orange; d(Rh-Rh) = 261, d(Re-N)axial = 219, d(Re-N)equat = 198 pm

[M(NCMe)2]+ [Ag(MeCN)2]B(C6H3(CF3)2)4 [Au(MeCN)2]SbF6

Mixed ligand examples Bis(benzonitrile)palladium dichloride (PdCl2(PhCN)2), an orange solid that serves as a source of "PdCl2" Tricarbonyltris(propionitrile)molybdenum(0) (Mo(CO)3(C2H5CN)3), a source of "Mo(CO)3". Related Cr and W complexes are known.

Complexes of η2-nitrile ligands Cases are known where nitriles function as η2-ligands. This bonding mode is more common for complexes of low-valence metals, such as Ni(0). Complexes of η2-nitriles are expected to form as transient intermediates in certain metal-catalyzed reactions of nitriles, such as the Hoesch reaction and the hydrogenation of nitriles. In some cases, η2-nitrile ligands are intermediates that preceded oxidative addition.

See also Cyanometalate – coordination compounds containing cyanide ligands (coordinating via C).

References

Illustrations

Worked examples

Example 1 — a first encounter with Transition metal nitrile complexes

Start with the simplest possible case. Write down what Transition metal nitrile complexes claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, 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 nitrile complexes 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 nitrile complexes 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 nitrile complexes

In research: Transition metal nitrile complexes appears in science 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 nitrile complexes 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 nitrile complexes is common in secondary-school and first-year university syllabi. It links to neighbouring topics Coordination complexes, Hexafluorophosphates, Tetrafluoroborates, so understanding it makes those chapters shorter.
In everyday life: Look for Transition metal nitrile complexes 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 nitrile complexes in 20 minutes

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Frequently asked questions

What is Transition metal nitrile complexes in simple terms?

Transition metal nitrile complexes are coordination compounds containing nitrile ligands. Because nitriles are weakly basic, the nitrile ligands in these complexes are often labile.

Why does Transition metal nitrile complexes matter?

Because it connects several science 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 nitrile complexes?

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 nitrile complexes.