Metal aromaticity or metalloaromaticity is the concept of aromaticity, found in many organic compounds, extended to metals and metal-containing compounds.[1] The first experimental evidence for the existence of aromaticity in metals was found in aluminium cluster compounds of the type MAl− 4 where M stands for lithium, sodium or copper.[2] These anions can be generated in a helium gas by laser vaporization of an aluminium / lithium carbonate composite or a copper or sodium / aluminium alloy, separated and selected by mass spectrometry and analyzed by photoelectron spectroscopy. The evidence for aromaticity in these compounds is based on several considerations. Computational chemistry shows that these aluminium clusters consist of a tetranuclear Al2− 4 plane and a counterion at the apex of a square pyramid. The Al2− 4 unit is perfectly planar and is not perturbed the presence of the counterion or even the presence of two counterions in the neutral compound M 2Al 4. In addition its HOMO is calculated to be a doubly occupied delocalized pi system making it obey Hückel's rule. Finally a match exists between the calculated values and the experimental photoelectron values for the energy required to remove the first 4 valence electrons. The first fully metal aromatic compound was a cyclogallane with a Ga32- core discovered by Gregory Robinson in 1995.[3]
D-orbital aromaticity is found in trinuclear tungstenW 3O− 9 and molybdenumMo 3O− 9metal clusters generated by laser vaporization of the pure metals in the presence of oxygen in a helium stream.[4] In these clusters the three metal centers are bridged by oxygen and each metal has two terminal oxygen atoms. The first signal in the photoelectron spectrum corresponds to the removal of the valence electron with the lowest energy in the anion to the neutral M 3O 9 compound. This energy turns out to be comparable to that of bulk tungsten trioxide and molybdenum trioxide. The photoelectric signal is also broad which suggests a large difference in conformation between the anion and the neutral species. Computational chemistry shows that the M 3O− 9 anions and M 3O2− 9 dianions are ideal hexagons with identical metal-to-metal bond lengths. Tritantalum oxide clusters (Ta3O3−) also are observed to exhibit possible D-orbital aromaticity.[3]
The molecules discussed thus far only exist diluted in the gas phase. A study exploring the properties of a compound formed in water from sodium molybdate (Na 2MoO 4·2H 2O) and iminodiacetic acid also revealed evidence of aromaticity, but this compound has actually been isolated. X-ray crystallography showed that the sodium atoms are arranged in layers of hexagonal clusters akin to pentacenes. The sodium-to-sodium bond lengths are unusually short (327 pm versus 380 pm in elemental sodium) and, like benzene, the ring is planar. In this compound each sodium atom has a distorted octahedral molecular geometry with coordination to molybdenum atoms and water molecules.[5] The experimental evidence is supported by computed NICS aromaticity values.
^Observation of All-Metal Aromatic Molecules Xi Li, Aleksey E. Kuznetsov, Hai-Feng Zhang, Alexander I. Boldyrev, Lai-Sheng Wang Science Vol. 291. p. 859 2001doi:10.1126/science.291.5505.859
^ abKrämer, Katrina. "The search for the grand unification of aromaticity". Chemistry World.
^Synthesis and structure of 1-D Na6 cluster chain with short Na–Na distance: Organic like aromaticity in inorganic metal cluster Snehadrinarayan Khatua, Debesh R. Roy, Pratim K. Chattaraj and Manish Bhattacharjee Chem. Commun., 2007, 135–37, doi:10.1039/b611693k
January 01, 1970
metal, aromaticity, metalloaromaticity, concept, aromaticity, found, many, organic, compounds, extended, metals, metal, containing, compounds, first, experimental, evidence, existence, aromaticity, metals, found, aluminium, cluster, compounds, type, where, sta. Metal aromaticity or metalloaromaticity is the concept of aromaticity found in many organic compounds extended to metals and metal containing compounds 1 The first experimental evidence for the existence of aromaticity in metals was found in aluminium cluster compounds of the type MAl 4 where M stands for lithium sodium or copper 2 These anions can be generated in a helium gas by laser vaporization of an aluminium lithium carbonate composite or a copper or sodium aluminium alloy separated and selected by mass spectrometry and analyzed by photoelectron spectroscopy The evidence for aromaticity in these compounds is based on several considerations Computational chemistry shows that these aluminium clusters consist of a tetranuclear Al2 4 plane and a counterion at the apex of a square pyramid The Al2 4 unit is perfectly planar and is not perturbed the presence of the counterion or even the presence of two counterions in the neutral compound M2 Al4 In addition its HOMO is calculated to be a doubly occupied delocalized pi system making it obey Huckel s rule Finally a match exists between the calculated values and the experimental photoelectron values for the energy required to remove the first 4 valence electrons The first fully metal aromatic compound was a cyclogallane with a Ga32 core discovered by Gregory Robinson in 1995 3 D orbital aromaticity is found in trinuclear tungsten W3 O 9 and molybdenum Mo3 O 9 metal clusters generated by laser vaporization of the pure metals in the presence of oxygen in a helium stream 4 In these clusters the three metal centers are bridged by oxygen and each metal has two terminal oxygen atoms The first signal in the photoelectron spectrum corresponds to the removal of the valence electron with the lowest energy in the anion to the neutral M3 O9 compound This energy turns out to be comparable to that of bulk tungsten trioxide and molybdenum trioxide The photoelectric signal is also broad which suggests a large difference in conformation between the anion and the neutral species Computational chemistry shows that the M3 O 9 anions and M3 O2 9 dianions are ideal hexagons with identical metal to metal bond lengths Tritantalum oxide clusters Ta3O3 also are observed to exhibit possible D orbital aromaticity 3 The molecules discussed thus far only exist diluted in the gas phase A study exploring the properties of a compound formed in water from sodium molybdate Na2 MoO4 2H2 O and iminodiacetic acid also revealed evidence of aromaticity but this compound has actually been isolated X ray crystallography showed that the sodium atoms are arranged in layers of hexagonal clusters akin to pentacenes The sodium to sodium bond lengths are unusually short 327 pm versus 380 pm in elemental sodium and like benzene the ring is planar In this compound each sodium atom has a distorted octahedral molecular geometry with coordination to molybdenum atoms and water molecules 5 The experimental evidence is supported by computed NICS aromaticity values See also editMetal cluster compound Cluster of three or more metals Catenation Bonding of atoms of the same element into chains or ringsReferences edit Feixas Ferran Matito Eduard Poater Jordi Sola Miquel 13 September 2012 Metalloaromaticity Wiley Interdisciplinary Reviews Computational Molecular Science 3 2 105 122 doi 10 1002 wcms 1115 S2CID 222199114 Observation of All Metal Aromatic Molecules Xi Li Aleksey E Kuznetsov Hai Feng Zhang Alexander I Boldyrev Lai Sheng Wang Science Vol 291 p 859 2001 doi 10 1126 science 291 5505 859 a b Kramer Katrina The search for the grand unification of aromaticity Chemistry World Observation of d Orbital Aromaticity Xin Huang Hua Jin Zhai Boggavarapu Kiran Lai Sheng Wang Angewandte Chemie International Edition Volume 44 Issue 44 Pages 7251 54 2005 doi 10 1002 anie 200502678 Synthesis and structure of 1 D Na6 cluster chain with short Na Na distance Organic like aromaticity in inorganic metal cluster Snehadrinarayan Khatua Debesh R Roy Pratim K Chattaraj and Manish Bhattacharjee Chem Commun 2007 135 37 doi 10 1039 b611693k Retrieved from https en wikipedia org w index php title Metal aromaticity amp oldid 1095159913, wikipedia, wiki, book, books, library,
