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Revision as of 18:44, 11 January 2025 editSmokefoot (talk | contribs)Autopatrolled, Extended confirmed users, Pending changes reviewers, Rollbackers74,902 edits ←Created page with ''''Transition metal hydroxide complexes''' are a large family of coordination complexes containing hydroxide (OH<sup>-</sup>) as a ligand. The inventory is very large. ==Representative complexes== ===Homoleptic complexes=== Only a few homoleptic hydroxide complexes are known: {{chem2|2-, 2-, and 2-}}.<ref>{{cite journal |doi=10.1021/cm101490w |title=Hydroxometalates from Anion Exchange Reactions of [BF<su...'  Latest revision as of 06:12, 13 January 2025 edit undoCitation bot (talk | contribs)Bots5,449,754 edits Altered template type. Add: isbn, series, bibcode. Removed parameters. Some additions/deletions were parameter name changes. | Use this bot. Report bugs. | Suggested by Graeme Bartlett | #UCB_toolbar 
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'''Transition metal hydroxide complexes''' are a large family of ]es containing ] (OH<sup>-</sup>) as a ]. The inventory is very large. '''Transition metal hydroxide complexes''' are ]es containing one or more ] (OH<sup>-</sup>) ]s. The inventory is very large.

==Hydroxide as a ligand==
Hydroxide is classified as an X ligand in the ]. In the ], it is a one-electron ligand when terminal and a three-electron ligand when doubly bridging.

From the electric structure perspective, hydroxide is a strong pi-donor ligand, akin to fluoride. One consequence is that few polyhydroxide complexes are low spin. Another consequence is that electron-precise hydroxide complexes tend to be rather nucleophilic.<ref name=Nolan>{{cite journal |doi=10.1016/j.ccr.2017.10.012 |title=Hydroxide complexes of the late transition metals: Organometallic chemistry and catalysis |date=2017 |last1=Nelson |first1=David J. |last2=Nolan |first2=Steven P. |journal=Coordination Chemistry Reviews |volume=353 |pages=278–294 |url=https://strathprints.strath.ac.uk/62176/1/Nelson_Nolan_CCR2017_Hydroxide_complexes_of_the_late_transition_metals.pdf }}</ref><ref>{{cite journal |doi=10.1021/ar000132x |title=Formation, Reactivity, and Properties of Nondative Late Transition Metal−Oxygen and −Nitrogen Bonds |date=2002 |last1=Fulton |first1=J. Robin |last2=Holland |first2=Andrew W. |last3=Fox |first3=Daniel J. |last4=Bergman |first4=Robert G. |journal=Accounts of Chemical Research |volume=35 |issue=1 |pages=44–56 |pmid=11790088 |pmc=1473979 }}</ref>


==Representative complexes== ==Representative complexes==
Many hydroxo complexes are prepared by treating metal halides with hydroxide salts. Hydrolysis of basic ligands (amides, alkyls) also produces hydroxide complexes.<ref name=Nolan/>

===Homoleptic complexes=== ===Homoleptic complexes===
Only a few homoleptic hydroxide complexes are known: {{chem2|2-, 2-, and 2-}}.<ref>{{cite journal |doi=10.1021/cm101490w |title=Hydroxometalates from Anion Exchange Reactions of &#91;BF<sub>4</sub>&#93;<sup>−</sup> based Ionic Liquids: Formation of &#91;M(OH)<sub>6</sub>)&#93;<sup>2−</sup> (M = Ti, Zr) and &#91;Zr(OH)<sub>5</sub>&#93;<sup>−</sup> |date=2010 |last1=Lin |first1=Hechun |last2=De Oliveira |first2=Peter W. |last3=Huch |first3=Volker |last4=Veith |first4=Michael |journal=Chemistry of Materials |volume=22 |issue=24 |pages=6518–6523 }}</ref> Only a few homoleptic hydroxide complexes are known. These include the d<sup>6</sup> species {{chem2|(2-)}}<ref>{{cite journal |doi=10.1107/S0567740882006311 |title=Ammonium hexahydroxoplatinat(IV) und Strukturverfeinerung für Kalium-hexahydroxoplatinat(IV) |date=1982 |last1=Bandel |first1=G. |last2=Platte |first2=C. |last3=Trömel |first3=M. |journal=Acta Crystallographica Section B Structural Crystallography and Crystal Chemistry |volume=38 |issue=5 |pages=1544–1546 |bibcode=1982AcCrB..38.1544B }}</ref> and the d<sup>0</sup> complexes {{chem2|(2-) and (2-)}}.<ref>{{cite journal |doi=10.1021/cm101490w |title=Hydroxometalates from Anion Exchange Reactions of &#91;BF<sub>4</sub>&#93;<sup>−</sup> based Ionic Liquids: Formation of &#91;M(OH)<sub>6</sub>)&#93;<sup>2−</sup> (M = Ti, Zr) and &#91;Zr(OH)<sub>5</sub>&#93;<sup>−</sup> |date=2010 |last1=Lin |first1=Hechun |last2=De Oliveira |first2=Peter W. |last3=Huch |first3=Volker |last4=Veith |first4=Michael |journal=Chemistry of Materials |volume=22 |issue=24 |pages=6518–6523 }}</ref>


===Mixed ligand complexes===
Many complexes are known where hydroxide shares the coordination sphere with other ligands. One pair of such complexes are {<sub>2</sub>(mu-OH)<sub>3</sub>}<sup>3+</sup> and its derivative {<sub>2</sub>(mu-OH)<sub>2</sub>}<sup>4+</sup>.<ref>{{cite book |doi=10.1002/9780470132548.ch21 |title=μ-Carboxylatodi-μ-Hydroxo-Bis&#91;Triamminecobalt(III)&#93; Complexes |series=Inorganic Syntheses |year=1985 |last1=Wieghardt |first1=K. |last2=Siebert |first2=H. |volume=23 |pages=107–116|isbn=978-0-471-81873-1 }}</ref>
]


==Reactions== ==Reactions==
Prominent reactions of metal hydroxides are their acid-base behavior. Protonation of metal hydroxides gives ]es: Prominent reactions of metal hydroxides are their acid-base behavior. Protonation of metal hydroxides gives ]es:
:{{chem2|LnM\sOH + H+ <-> LnM\sOH2+}} :{{chem2|L_{n}M\sOH + H+ <-> L_{n}M\sOH2+}} where {{chem2|L_{n} }} is the ligand complement on the metal M

Thus, aquo ligand is a ], of comparable strength to ] (p''K''<sub>a</sub> of about 4.8).<ref name=Lincoln>{{cite book|first1=S. F. |last1=Lincoln|first2=D. T.|last2=Richens|first3=A. G.|last3=Sykes|title=Comprehensive Coordination Chemistry II|chapter=Metal Aqua Ions|year=2003|volume=1|pages=515–555|doi=10.1016/B0-08-043748-6/01055-0|isbn=9780080437484}}</ref>

In principle but not very commonly, metal hydroxides undergo deprotonation, yielding ]es: In principle but not very commonly, metal hydroxides undergo deprotonation, yielding ]es:
:{{chem2|LnM\sOH <-> LnM\dO- +H+}} :{{chem2|L_{n}M\sOH <-> L_{n}M\dO- +H+}}


Characteristically, hydroxide ligands are compact and basic. They tend to function as ]s. One manifestation of this property is the preponderance of di-and polymetallic hydroxide complexes. A practical consequence of this feature is the tendency of metal aquo complexes to form precipitates of meta hydroxides. Characteristically, hydroxide ligands are compact and basic. They tend to function as ]s. One manifestation of this property is the preponderance of di-and polymetallic hydroxide complexes. A practical consequence of this feature is the tendency of metal aquo complexes to form precipitates of meta hydroxides.


===Bioinorganic chemistry===
The hydroxo ligand is a nucleophile. This behavior is relevant to their role in enzymology. In ], a zinc hydroxide binds ]:
:]
⚫ :{{chem2|LnM\sOH + CO2 <-> LnMO\sO\sCO2H}}
]s, ]s responsible for ] (O<sub>2</sub>) transport in some animals have an diiron hydroxide active site. The hydroxide ligand engages the bound O2 through ].

The nucleophilicity of hydroxo ligands is relevant to the role of some M-OH centers in enzymology. For example, in ], a zinc hydroxide binds ]:<ref>{{cite journal |doi=10.1021/cr0206263 |title=Synthetic Analogues Relevant to the Structure and Function of Zinc Enzymes |date=2004 |last1=Parkin |first1=Gerard |journal=Chemical Reviews |volume=104 |issue=2 |pages=699–768 |pmid=14871139 }}</ref>
⚫ :{{chem2|L_{n}M\sOH + CO2 <-> L_{n}MO\sO\sCO2H}}

The ] (OEC) consists of a Mn-Ca-O-OH cluster that is responsible for the biosynthesis of O<sub>2</sub>. It is proposed that the O-O bond forming step involves a hydroxide ligand.

]s catalyze the hydrolysis peptide bond. The catalytic center is such enzymes often involves metal hydroxides.


==References== ==References==
<references /> <references />

{{Coordination complexes}}

]

Latest revision as of 06:12, 13 January 2025

Transition metal hydroxide complexes are coordination complexes containing one or more hydroxide (OH) ligands. The inventory is very large.

Hydroxide as a ligand

Hydroxide is classified as an X ligand in the Covalent bond classification method. In the usual electron counting method, it is a one-electron ligand when terminal and a three-electron ligand when doubly bridging.

From the electric structure perspective, hydroxide is a strong pi-donor ligand, akin to fluoride. One consequence is that few polyhydroxide complexes are low spin. Another consequence is that electron-precise hydroxide complexes tend to be rather nucleophilic.

Representative complexes

Many hydroxo complexes are prepared by treating metal halides with hydroxide salts. Hydrolysis of basic ligands (amides, alkyls) also produces hydroxide complexes.

Homoleptic complexes

Only a few homoleptic hydroxide complexes are known. These include the d species [Pt(OH)6] and the d complexes [Ti(OH)6] and [Zr2(OH)8(mu−OH)2].

Mixed ligand complexes

Many complexes are known where hydroxide shares the coordination sphere with other ligands. One pair of such complexes are {2(mu-OH)3} and its derivative {2(mu-OH)2}.

protonolysis of mu-OH cobalt complex
protonolysis of mu-OH cobalt complex

Reactions

Prominent reactions of metal hydroxides are their acid-base behavior. Protonation of metal hydroxides gives aquo complexes:

LnM−OH + H ⇌ LnM−OH+2 where Ln is the ligand complement on the metal M

Thus, aquo ligand is a weak acid, of comparable strength to acetic acid (pKa of about 4.8).

In principle but not very commonly, metal hydroxides undergo deprotonation, yielding oxo complexes:

LnM−OH ⇌ LnM=O +H

Characteristically, hydroxide ligands are compact and basic. They tend to function as bridging ligands. One manifestation of this property is the preponderance of di-and polymetallic hydroxide complexes. A practical consequence of this feature is the tendency of metal aquo complexes to form precipitates of meta hydroxides.

Bioinorganic chemistry

Active site of hemerythrin before and after oxygenation.

Hemerythrins, proteins responsible for oxygen (O2) transport in some animals have an diiron hydroxide active site. The hydroxide ligand engages the bound O2 through hydrogen bonding.

The nucleophilicity of hydroxo ligands is relevant to the role of some M-OH centers in enzymology. For example, in carbonic anhydrase, a zinc hydroxide binds carbon dioxide:

LnM−OH + CO2 ⇌ LnMO−O−CO2H

The oxygen evolving complex (OEC) consists of a Mn-Ca-O-OH cluster that is responsible for the biosynthesis of O2. It is proposed that the O-O bond forming step involves a hydroxide ligand.

Metalloproteinases catalyze the hydrolysis peptide bond. The catalytic center is such enzymes often involves metal hydroxides.

References

  1. ^ Nelson, David J.; Nolan, Steven P. (2017). "Hydroxide complexes of the late transition metals: Organometallic chemistry and catalysis" (PDF). Coordination Chemistry Reviews. 353: 278–294. doi:10.1016/j.ccr.2017.10.012.
  2. Fulton, J. Robin; Holland, Andrew W.; Fox, Daniel J.; Bergman, Robert G. (2002). "Formation, Reactivity, and Properties of Nondative Late Transition Metal−Oxygen and −Nitrogen Bonds". Accounts of Chemical Research. 35 (1): 44–56. doi:10.1021/ar000132x. PMC 1473979. PMID 11790088.
  3. Bandel, G.; Platte, C.; Trömel, M. (1982). "Ammonium hexahydroxoplatinat(IV) und Strukturverfeinerung für Kalium-hexahydroxoplatinat(IV)". Acta Crystallographica Section B Structural Crystallography and Crystal Chemistry. 38 (5): 1544–1546. Bibcode:1982AcCrB..38.1544B. doi:10.1107/S0567740882006311.
  4. Lin, Hechun; De Oliveira, Peter W.; Huch, Volker; Veith, Michael (2010). "Hydroxometalates from Anion Exchange Reactions of [BF4] based Ionic Liquids: Formation of [M(OH)6)] (M = Ti, Zr) and [Zr(OH)5]". Chemistry of Materials. 22 (24): 6518–6523. doi:10.1021/cm101490w.
  5. Wieghardt, K.; Siebert, H. (1985). μ-Carboxylatodi-μ-Hydroxo-Bis[Triamminecobalt(III)] Complexes. Inorganic Syntheses. Vol. 23. pp. 107–116. doi:10.1002/9780470132548.ch21. ISBN 978-0-471-81873-1.
  6. Lincoln, S. F.; Richens, D. T.; Sykes, A. G. (2003). "Metal Aqua Ions". Comprehensive Coordination Chemistry II. Vol. 1. pp. 515–555. doi:10.1016/B0-08-043748-6/01055-0. ISBN 9780080437484.
  7. Parkin, Gerard (2004). "Synthetic Analogues Relevant to the Structure and Function of Zinc Enzymes". Chemical Reviews. 104 (2): 699–768. doi:10.1021/cr0206263. PMID 14871139.
Coordination complexes
H donors:
B donors:
C donors:
Si donors:
N donors:
P donors:
O donors:
S donors:
Halide donors:
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