In coordination chemistry, metal ammine complexes are metal complexes containing at least one ammonia (NH3) ligand. "Ammine" is spelled this way due to historical reasons[citation needed]; in contrast, alkyl or aryl bearing ligands are spelt with a single "m". Almost all metal ions bind ammonia as a ligand, but the most prevalent examples of ammine complexes are for Cr(III), Co(III), Ni(II), Cu(II) as well as several platinum group metals.[1]
Ball-and-stick model of the tetraamminediaquacopper(II) cation, [Cu(NH3)4(H2O)2]2+
Structural representations used by Alfred Werner (right) and Sophus Mads Jørgensen for one isomer of the dichloride salt of the complex [Pt(NH3)2(pyridine)2]2+.[2]
Ammine complexes played a major role in the development of coordination chemistry, specifically determination of the stereochemistry and structure. They are easily prepared, and the metal-nitrogen ratio can be determined by elemental analysis. Through studies mainly on the ammine complexes, Alfred Werner developed his Nobel Prize-winning concept of the structure of coordination compounds (see Figure).[3][1]
One of the first ammine complexes to be described was Magnus' green salt, which consists of the platinum tetrammine complex [Pt(NH3)4]2+.[4]
Structure and bonding
Ammonia is a Lewis base and a "pure" sigma donor. It is also compact such that steric effects are negligible. These factors simplify interpretation of structural and spectroscopic results.The Co–N distances in complexes [M(NH3)6]n+ have been examined closely by X-ray crystallography.[5]
M–N distances for [M(NH3)6]n+
M
n+
M–N distance (Å)
d-electron configuration
comment
Co
3+
1.936
t2g6 eg0
low-spin trications are small
Co
2+
2.114
t2g5 eg2
population of eg orbital and lower positive charge
Ru
3+
2.104
t2g5 eg0
low spin trication, but Ru is intrinsically larger than Co
Ru
2+
2.144
t2g6 eg0
low spin dication
Examples
Homoleptic poly(ammine) complexes are known for many of the transition metals. Most often, they have the formula [M(NH3)6]n+ where n = 2, 3, and even 4 (M = Pt).[6]
The ammines of chromium(III) and cobalt(III) are of historic significance. Both families of ammines are relatively inert kinetically, which allows the separation of isomers.[7] For example, tetraamminedichlorochromium(III) chloride, [Cr(NH3)4Cl2]Cl, has two forms - the cis isomer is violet, while the trans isomer is green. The trichloride of the hexaammine (hexamminecobalt(III) chloride, [Co(NH3)6]Cl3) exists as only a single isomer. "Reinecke's salt" with the formula [NH4][Cr(NCS)4(NH3)2]·H2O was first reported in 1863.[8]
Nickel(II), zinc(II), copper(II)
Sample of chloropentamminecobalt chloride[CoCl(NH3)5]Cl2, illustrating the vibrant colors typical of transition metal ammine complexes.
Zinc(II) forms a colorless tetraammine with the formula [Zn(NH3)4]2+.[9] Like most zinc complexes, it has a tetrahedral structure. Hexaamminenickel is violet, and the copper(II) complex is deep blue. The latter is characteristic of the presence of copper(II) in qualitative inorganic analysis.
Copper(I), silver(I), and gold(I)
Copper(I) forms only labile complexes with ammonia, including the trigonal planar [Cu(NH3)3]+.[10] Silver gives the diammine complex [Ag(NH3)2]+ with linear coordination geometry.[11] It is this complex that forms when otherwise rather insoluble silver chloride dissolves in aqueous ammonia. The same complex is the active ingredient in Tollens' reagent. Gold(I) chloride reacts with ammonia to form [Au(NH3)2]+.[12]
Reactions
Ligand exchange and redox reactions
Since ammonia is a stronger ligand in the spectrochemical series than water, metal ammine complexes are stabilized relative to the corresponding aquo complexes. For similar reasons, metal ammine complexes are less strongly oxidizing than are the corresponding aquo complexes. The latter property is illustrated by the stability of [Co(NH3)6]3+ in aqueous solution and the nonexistence of [Co(H2O)6]3+ (which would oxidize water).
Acid-base reactions
Once complexed to a metal ion, ammonia is no longer basic. This property is illustrated by the stability of some metal ammine complexes in strong acid solutions. When the M–NH3 bond is weak, the ammine ligand dissociates and protonation ensues. The behavior is illustrated by the respective non-reaction and reaction with [Co(NH3)6]3+ and [Ni(NH3)6]2+ toward aqueous acids.
The ammine ligands are more acidic than is ammonia (pKa ~ 33). For highly cationic complexes such as [Pt(NH3)6]4+, the conjugate base can be obtained. The deprotonation of cobalt(III) ammine-halide complexes, e.g. [CoCl(NH3)5]2+ labilises the Co–Cl bond, according to the Sn1CB mechanism.
Oxidation of ammonia
Deprotonation can be combined with oxidation, allowing the conversion of ammine complexes into nitrosyl complexes:[13]
This behavior is relevant to the use of ammonia as a hydrogen source.
Applications
Metal ammine complexes find many uses. Cisplatin (cis-[PtCl2(NH3)2]) is a drug used in treating cancer.[14] Many other amine complexes of the platinum group metals have been evaluated for this application.
In the separation of the individual platinum metals from their ore, several schemes rely on the precipitation of [RhCl(NH3)5]Cl2. In some separation schemes, palladium is purified by manipulating equilibria involving [Pd(NH3)4]Cl2, [PdCl2(NH3)2], and [Pt(NH3)4][PdCl4].
In the processing of cellulose, the copper ammine complex known as Schweizer's reagent ([Cu(NH3)4(H2O)2](OH)2) is sometimes used to solubilise the polymer. Schweizer's reagent is prepared by treating an aqueous solutions of copper(II) ions with ammonia. Initially, the light blue hydroxide precipitates only to redissolve upon addition of more ammonia:
^ abA. von Zelewsky "Stereochemistry of Coordination Compounds" John Wiley: Chichester, 1995. ISBN0-471-95599-X.
^Alfred Werner "Beitrag zur Konstitution anorganischer Verbindungen" Zeitschrift für anorganische Chemie 1893, Volume 3, pages 267–330.doi:10.1002/zaac.18930030136
^"Werner Centennial" George B. Kauffman, Ed. Adv. Chem. Ser., 1967, Volume 62. ISBN978-0-8412-0063-0
^Atoji, M.; Richardson, J. W.; Rundle, R. E. (1957). "On the Crystal Structures of the Magnus Salts, Pt(NH3)4PtCl4". J. Am. Chem. Soc.79 (12): 3017–3020. doi:10.1021/ja01569a009.
^Hair, Neil J.; Beattie, James K. (1977). "Structure of Hexaaquairon(III) Nitrate Trihydrate. Comparison of Iron(II) and Iron(III) Bond Lengths in High-Spin Octahedral Environments". Inorganic Chemistry. 16 (2): 245–250. doi:10.1021/ic50168a006.
^Eßmann, Ralf; Kreiner, Guido; Niemann, Anke; Rechenbach, Dirk; Schmieding, Axel; Sichla, Thomas; Zachwieja, Uwe; Jacobs, Herbert (1996). "Isotype Strukturen einiger Hexaamminmetall(II)-halogenide von 3d-Metallen: [V(NH3)6]I2, [Cr(NH3)6]I2, [Mn(NH3)6]Cl2, [Fe(NH3)6]Cl2, [Fe(NH3)6]Br2, [Co(NH3)6]Br2, und [Ni(NH3)6]Cl2". Zeitschrift für anorganische und allgemeine Chemie. 622 (7): 1161–1166. doi:10.1002/zaac.19966220709.
^Basolo, F.; Pearson, R. G. "Mechanisms of Inorganic Reactions." John Wiley and Son: New York: 1967. ISBN0-471-05545-X
^Reinecke, A. "Über Rhodanchromammonium-Verbindungen" Annalen der Chemie und Pharmacie, volume 126, pages 113-118 (1863). doi:10.1002/jlac.18631260116.
^Essmann, R. (1995). "Influence of coordination on N-H...X- hydrogen bonds. Part 1. [Zn(NH3)4]Br2 and [Zn(NH3)4]I2". Journal of Molecular Structure. 356 (3): 201–6. Bibcode:1995JMoSt.356..201E. doi:10.1016/0022-2860(95)08957-W.
^Nilsson, Kersti B.; Persson, Ingmar (2004). "The coordination chemistry of copper(I) in liquid ammonia, trialkyl and triphenyl phosphite, and tri-n-butylphosphine solution". Dalton Transactions (9): 1312–1319. doi:10.1039/B400888J. PMID 15252623.
^Nilsson, K. B.; Persson, I.; Kessler, V. G. (2006). "Coordination Chemistry of the Solvated AgI and AuI Ions in Liquid and Aqueous Ammonia, Trialkyl and Triphenyl Phosphite, and Tri-n-butylphosphine Solutions". Inorganic Chemistry. 45 (17): 6912–6921. doi:10.1021/ic060175v. PMID 16903749.
^Scherf, L. M.; Baer, S. A.; Kraus, F.; Bawaked, S. M.; Schmidbaur, H. (2013). "Implications of the Crystal Structure of the Ammonia Solvate [Au(NH3)2]Cl·4NH3". Inorganic Chemistry. 52 (4): 2157–2161. doi:10.1021/ic302550q. PMID 23379897.
^ abDunn, Peter L.; Cook, Brian J.; Johnson, Samantha I.; Appel, Aaron M.; Bullock, R. Morris (2020). "Oxidation of Ammonia with Molecular Complexes". Journal of the American Chemical Society. 142 (42): 17845–17858. doi:10.1021/jacs.0c08269. OSTI 1706682. PMID 32977718. S2CID 221938378.
^S. J. Lippard, J. M. Berg "Principles of Bioinorganic Chemistry" University Science Books: Mill Valley, CA; 1994. ISBN0-935702-73-3.
^Rosenblatt, A.; Stamford, T. C. M.; Niederman, R. (2009). "Silver diamine fluoride: a caries "silver-fluoride bullet"". Journal of Dental Research. 88 (2): 116–125. doi:10.1177/0022034508329406. PMID 19278981. S2CID 30730306.{{cite journal}}: CS1 maint: uses authors parameter (link)
January 28, 2023
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In coordination chemistry metal ammine complexes are metal complexes containing at least one ammonia NH3 ligand Ammine is spelled this way due to historical reasons citation needed in contrast alkyl or aryl bearing ligands are spelt with a single m Almost all metal ions bind ammonia as a ligand but the most prevalent examples of ammine complexes are for Cr III Co III Ni II Cu II as well as several platinum group metals 1 Ball and stick model of the tetraamminediaquacopper II cation Cu NH3 4 H2O 2 2 Contents 1 History 2 Structure and bonding 3 Examples 3 1 Platinum group metals 3 2 Cobalt III and chromium III 3 3 Nickel II zinc II copper II 3 4 Copper I silver I and gold I 4 Reactions 4 1 Ligand exchange and redox reactions 4 2 Acid base reactions 4 3 Oxidation of ammonia 4 4 H atom transfer 5 Applications 6 See also 7 ReferencesHistory Edit Structural representations used by Alfred Werner right and Sophus Mads Jorgensen for one isomer of the dichloride salt of the complex Pt NH3 2 pyridine 2 2 2 Ammine complexes played a major role in the development of coordination chemistry specifically determination of the stereochemistry and structure They are easily prepared and the metal nitrogen ratio can be determined by elemental analysis Through studies mainly on the ammine complexes Alfred Werner developed his Nobel Prize winning concept of the structure of coordination compounds see Figure 3 1 One of the first ammine complexes to be described was Magnus green salt which consists of the platinum tetrammine complex Pt NH3 4 2 4 Structure and bonding EditAmmonia is a Lewis base and a pure sigma donor It is also compact such that steric effects are negligible These factors simplify interpretation of structural and spectroscopic results The Co N distances in complexes M NH3 6 n have been examined closely by X ray crystallography 5 M N distances for M NH3 6 n M n M N distance A d electron configuration commentCo 3 1 936 t2g6 eg0 low spin trications are smallCo 2 2 114 t2g5 eg2 population of eg orbital and lower positive chargeRu 3 2 104 t2g5 eg0 low spin trication but Ru is intrinsically larger than CoRu 2 2 144 t2g6 eg0 low spin dicationExamples EditHomoleptic poly ammine complexes are known for many of the transition metals Most often they have the formula M NH3 6 n where n 2 3 and even 4 M Pt 6 Platinum group metals Edit Platinum group metals form diverse ammine complexes Pentaamine dinitrogen ruthenium II and the Creutz Taube complex are well studied examples of historic significance The complex cis PtCl2 NH3 2 under the name Cisplatin is an important anticancer drug Pentamminerhodium chloride RhCl NH3 5 2 is an intermediate in the purification of rhodium from its ores Metal Ammine Complexes Carboplatin a widely used anticancer drug Pentamminerhodium chloride the dichloride salt of a pentammine halide complex Pentaamine dinitrogen ruthenium II the first metal dinitrogen complex Hexamminecobalt III chloride the trichloride salt of the hexammine complex Co NH3 6 3 It is famously stable in concentrated hydrochloric acid Reinecke s salt features a very stable anionic diamine complex of Cr III which is used as a counteranion Cobalt III and chromium III Edit The ammines of chromium III and cobalt III are of historic significance Both families of ammines are relatively inert kinetically which allows the separation of isomers 7 For example tetraamminedichlorochromium III chloride Cr NH3 4Cl2 Cl has two forms the cis isomer is violet while the trans isomer is green The trichloride of the hexaammine hexamminecobalt III chloride Co NH3 6 Cl3 exists as only a single isomer Reinecke s salt with the formula NH4 Cr NCS 4 NH3 2 H2O was first reported in 1863 8 Nickel II zinc II copper II Edit Sample of chloropentamminecobalt chloride CoCl NH3 5 Cl2 illustrating the vibrant colors typical of transition metal ammine complexes Zinc II forms a colorless tetraammine with the formula Zn NH3 4 2 9 Like most zinc complexes it has a tetrahedral structure Hexaamminenickel is violet and the copper II complex is deep blue The latter is characteristic of the presence of copper II in qualitative inorganic analysis Copper I silver I and gold I Edit Copper I forms only labile complexes with ammonia including the trigonal planar Cu NH3 3 10 Silver gives the diammine complex Ag NH3 2 with linear coordination geometry 11 It is this complex that forms when otherwise rather insoluble silver chloride dissolves in aqueous ammonia The same complex is the active ingredient in Tollens reagent Gold I chloride reacts with ammonia to form Au NH3 2 12 Reactions EditLigand exchange and redox reactions Edit Since ammonia is a stronger ligand in the spectrochemical series than water metal ammine complexes are stabilized relative to the corresponding aquo complexes For similar reasons metal ammine complexes are less strongly oxidizing than are the corresponding aquo complexes The latter property is illustrated by the stability of Co NH3 6 3 in aqueous solution and the nonexistence of Co H2O 6 3 which would oxidize water Acid base reactions Edit Once complexed to a metal ion ammonia is no longer basic This property is illustrated by the stability of some metal ammine complexes in strong acid solutions When the M NH3 bond is weak the ammine ligand dissociates and protonation ensues The behavior is illustrated by the respective non reaction and reaction with Co NH3 6 3 and Ni NH3 6 2 toward aqueous acids The ammine ligands are more acidic than is ammonia pKa 33 For highly cationic complexes such as Pt NH3 6 4 the conjugate base can be obtained The deprotonation of cobalt III ammine halide complexes e g CoCl NH3 5 2 labilises the Co Cl bond according to the Sn1CB mechanism Oxidation of ammonia Edit Deprotonation can be combined with oxidation allowing the conversion of ammine complexes into nitrosyl complexes 13 H2O Ru terpy bipy NH3 Ru terpy bipy NO 2 5 H 6 e H atom transfer Edit In some ammine complexes the N H bond is weak Thus one tungsten ammine complex evolve hydrogen 13 2 W terpy PMe2Ph 2 NH3 2 W terpy PMe2Ph 2 NH2 H2This behavior is relevant to the use of ammonia as a hydrogen source Applications EditMetal ammine complexes find many uses Cisplatin cis PtCl2 NH3 2 is a drug used in treating cancer 14 Many other amine complexes of the platinum group metals have been evaluated for this application In the separation of the individual platinum metals from their ore several schemes rely on the precipitation of RhCl NH3 5 Cl2 In some separation schemes palladium is purified by manipulating equilibria involving Pd NH3 4 Cl2 PdCl2 NH3 2 and Pt NH3 4 PdCl4 In the processing of cellulose the copper ammine complex known as Schweizer s reagent Cu NH3 4 H2O 2 OH 2 is sometimes used to solubilise the polymer Schweizer s reagent is prepared by treating an aqueous solutions of copper II ions with ammonia Initially the light blue hydroxide precipitates only to redissolve upon addition of more ammonia Cu H2O 6 2 2 OH Cu OH 2 6 H2O Cu OH 2 4 NH3 2 H2O Cu NH3 4 H2O 2 2 2 OH Silver diammine fluoride Ag NH3 2 F is a topical medicament drug used to treat and prevent dental caries cavities and relieve dentinal hypersensitivity 15 See also EditLigand field theoryReferences Edit a b A von Zelewsky Stereochemistry of Coordination Compounds John Wiley Chichester 1995 ISBN 0 471 95599 X Alfred Werner Beitrag zur Konstitution anorganischer Verbindungen Zeitschrift fur anorganische Chemie 1893 Volume 3 pages 267 330 doi 10 1002 zaac 18930030136 Werner Centennial George B Kauffman Ed Adv Chem Ser 1967 Volume 62 ISBN 978 0 8412 0063 0 Atoji M Richardson J W Rundle R E 1957 On the Crystal Structures of the Magnus Salts Pt NH3 4PtCl4 J Am Chem Soc 79 12 3017 3020 doi 10 1021 ja01569a009 Hair Neil J Beattie James K 1977 Structure of Hexaaquairon III Nitrate Trihydrate Comparison of Iron II and Iron III Bond Lengths in High Spin Octahedral Environments Inorganic Chemistry 16 2 245 250 doi 10 1021 ic50168a006 Essmann Ralf Kreiner Guido Niemann Anke Rechenbach Dirk Schmieding Axel Sichla Thomas Zachwieja Uwe Jacobs Herbert 1996 Isotype Strukturen einiger Hexaamminmetall II halogenide von 3d Metallen V NH3 6 I2 Cr NH3 6 I2 Mn NH3 6 Cl2 Fe NH3 6 Cl2 Fe NH3 6 Br2 Co NH3 6 Br2 und Ni NH3 6 Cl2 Zeitschrift fur anorganische und allgemeine Chemie 622 7 1161 1166 doi 10 1002 zaac 19966220709 Basolo F Pearson R G Mechanisms of Inorganic Reactions John Wiley and Son New York 1967 ISBN 0 471 05545 X Reinecke A Uber Rhodanchromammonium Verbindungen Annalen der Chemie und Pharmacie volume 126 pages 113 118 1863 doi 10 1002 jlac 18631260116 Essmann R 1995 Influence of coordination on N H X hydrogen bonds Part 1 Zn NH3 4 Br2 and Zn NH3 4 I2 Journal of Molecular Structure 356 3 201 6 Bibcode 1995JMoSt 356 201E doi 10 1016 0022 2860 95 08957 W Nilsson Kersti B Persson Ingmar 2004 The coordination chemistry of copper I in liquid ammonia trialkyl and triphenyl phosphite and tri n butylphosphine solution Dalton Transactions 9 1312 1319 doi 10 1039 B400888J PMID 15252623 Nilsson K B Persson I Kessler V G 2006 Coordination Chemistry of the Solvated AgI and AuI Ions in Liquid and Aqueous Ammonia Trialkyl and Triphenyl Phosphite and Tri n butylphosphine Solutions Inorganic Chemistry 45 17 6912 6921 doi 10 1021 ic060175v PMID 16903749 Scherf L M Baer S A Kraus F Bawaked S M Schmidbaur H 2013 Implications of the Crystal Structure of the Ammonia Solvate Au NH3 2 Cl 4NH3 Inorganic Chemistry 52 4 2157 2161 doi 10 1021 ic302550q PMID 23379897 a b Dunn Peter L Cook Brian J Johnson Samantha I Appel Aaron M Bullock R Morris 2020 Oxidation of Ammonia with Molecular Complexes Journal of the American Chemical Society 142 42 17845 17858 doi 10 1021 jacs 0c08269 OSTI 1706682 PMID 32977718 S2CID 221938378 S J Lippard J M Berg Principles of Bioinorganic Chemistry University Science Books Mill Valley CA 1994 ISBN 0 935702 73 3 Rosenblatt A Stamford T C M Niederman R 2009 Silver diamine fluoride a caries silver fluoride bullet Journal of Dental Research 88 2 116 125 doi 10 1177 0022034508329406 PMID 19278981 S2CID 30730306 a href Template Cite journal html title Template Cite journal cite journal a CS1 maint uses authors parameter link Retrieved from https en wikipedia org w index php title Metal ammine complex amp oldid 1112203864, wikipedia, wiki, book, books, library,
