Wikipedia

Stacking (chemistry)

(Redirected fromPi stacking)

Inchemistry,stackingrefers to superposition of molecules or atomic sheets owing to attractive interactions between these molecules or sheets.

Metal dichalcogenide compounds

edit
MoS2,the most common metal dichalcogenide, adopts a layered structure.

Metal dichalcogenides have the formula ME2,where M = a transition metal and E = S, Se, Te.[1]In terms of their electronic structures, these compounds are usually viewed as derivatives of M4+.They adopt stacked structures, which is relevant to their ability to undergointercalation,e.g. bylithium,and theirlubricating properties.The corresponding diselenides and even ditellurides are known, e.g.,TiSe2,MoSe2,andWSe2.

Charge transfer salts

edit

Edge-on view of portion of crystal structure of hexamethyleneTTF/TCNQ charge transfer salt, highlighting the segregated stacking.[2]

A combination oftetracyanoquinodimethane(TCNQ) andtetrathiafulvalene(TTF) forms a strong charge-transfer complex referred to asTTF-TCNQ.[3]The solid shows almost metallic electrical conductance. In a TTF-TCNQ crystal, TTF and TCNQ molecules are arranged independently in separate parallel-aligned stacks, and an electron transfer occurs from donor (TTF) to acceptor (TCNQ) stacks.[4]

Graphite

edit
Side view of ABA layer stacking in graphite

Graphiteconsists of stacked sheets of covalently bonded carbon.[5][6]The individual layers are calledgraphene.In each layer, each carbon atom is bonded to three other atoms forming a continuous layer of sp2bonded carbon hexagons, like ahoneycomb latticewith a bond length of 0.142 nm, and the distance between planes is 0.335 nm.[7]Bonding between layers is relatively weakvan der Waals bonds,which allows the graphene-like layers to be easily separated and to glide past each other.[8]Electrical conductivity perpendicular to the layers is consequently about 1000 times lower.[9]

Linear chain compounds

edit

Linear chain compoundsare materials composed of stacked arrays ofmetal-metal bondedmolecules orions.Such materials exhibitanisotropicelectricalconductivity.[10]One example isRh(acac)(CO)2(acac =acetylacetonate,which stack withRh···Rhdistances of about 326pm.[11]Classic examples includeKrogmann's saltandMagnus's green salt.

Portion of the lattice ofDicarbonyl(acetylacetonato)rhodium(I)(Rh(acac)(CO)2) showing the "stacking" of the individual planar units throughRh···Rhinteractions.
edit
Main article:Pi-stacking

π–π stackingis anoncovalentinteraction between thepi bondsofaromaticrings.[12]Such "sandwich interactions" are however generallyelectrostaticallyrepulsive. What is more commonly observed areeither astaggered stacking(parallel displaced) orpi-teeing(perpendicular T-shaped) interaction both of which are electrostatic attractive.[13]For example, the most commonly observed interactions between aromatic rings of amino acid residues in proteins is a staggered stacked followed by a perpendicular orientation. Sandwiched orientations are relatively rare.[14]Pi stacking is repulsive as it places carbon atoms with partial negative charges from one ring on top of other partial negatively charged carbon atoms from the second ring and hydrogen atoms with partial positive charges on top of other hydrogen atoms that likewise carry partial positive charges.[15]

The synthesis of catenane exploiting attractive pi-stacking interactions between electron-rich and electron-poor arenes.

π–π interactions play a role insupramolecular chemistry,specifically the synthesis ofcatenane.The major challenge for the synthesis of catenane is to interlock molecules in a controlled fashion. Attractive π–π interactions exist between electron-rich benzene derivatives and electron-poor pyridinium rings.[16][2]Catanene was synthesized by treating bis(pyridinium) (A), bisparaphenylene-34-crown-10 (B), and 1, 4-bis(bromomethyl)benzene (C) (Fig. 2). The π–π interaction betweenAandBdirected the formation of an interlocked template intermediate that was further cyclized by substitution reaction with compoundCto generate the [2]catenane product.

See also

edit

References

edit
  1. ^Wells, A.F. (1984) Structural Inorganic Chemistry, Oxford: Clarendon Press.ISBN0-19-855370-6.
  2. ^D. Chasseau; G. Comberton; J. Gaultier; C. Hauw (1978). "Réexamen de la structure du complexe hexaméthylène-tétrathiafulvalène-tétracyanoquinodiméthane".Acta Crystallographica Section B.34(2): 689.Bibcode:1978AcCrB..34..689C.doi:10.1107/S0567740878003830.
  3. ^P. W. Anderson; P. A. Lee; M. Saitoh (1973). "Remarks on giant conductivity in TTF-TCNQ".Solid State Communications.13(5): 595–598.Bibcode:1973SSCom..13..595A.doi:10.1016/S0038-1098(73)80020-1.
  4. ^Van De Wouw, Heidi L.; Chamorro, Juan; Quintero, Michael; Klausen, Rebekka S. (2015). "Opposites Attract: Organic Charge Transfer Salts".Journal of Chemical Education.92(12): 2134–2139.Bibcode:2015JChEd..92.2134V.doi:10.1021/acs.jchemed.5b00340.
  5. ^Delhaes, Pierre (2000). "Polymorphism of carbon". In Delhaes, Pierre (ed.).Graphite and precursors.Gordon & Breach. pp. 1–24.ISBN9789056992286.
  6. ^Pierson, Hugh O. (2012).Handbook of carbon, graphite, diamond, and fullerenes: properties, processing, and applications.Noyes Publications. pp. 40–41.ISBN9780815517399.
  7. ^Delhaes, P. (2001).Graphite and Precursors.CRC Press.ISBN978-90-5699-228-6.
  8. ^Chung, D. D. L. (2002). "Review Graphite".Journal of Materials Science.37(8): 1475–1489.doi:10.1023/A:1014915307738.S2CID189839788.
  9. ^Pierson, Hugh O. (1993).Handbook of carbon, graphite, diamond, and fullerenes: properties, processing, and applications.Park Ridge, N.J.: Noyes Publications.ISBN0-8155-1739-4.OCLC49708274.
  10. ^Bera, J. K.; Dunbar, K. R. (2002). "Chain Compounds Based on Transition Metal Backbones: New Life for an Old Topic".Angew. Chem. Int. Ed.41(23): 4453–4457.doi:10.1002/1521-3773(20021202)41:23<4453::AID-ANIE4453>3.0.CO;2-1.PMID12458505.
  11. ^Huq, Fazlul; Skapski, Andrzej C. (1974). "Refinement of the crystal structure of acetylacetonatodicarbonylrhodium(I)".J. Cryst. Mol. Struct.4(6): 411–418.doi:10.1007/BF01220097.S2CID96977904.
  12. ^Smith, Michael B.;March, Jerry(2007),Advanced Organic Chemistry: Reactions, Mechanisms, and Structure(6th ed.), New York: Wiley-Interscience, p. 114,ISBN978-0-471-72091-1
  13. ^Lewis M, Bagwill C, Hardebeck L, Wireduaah S (2016)."Modern Computational Approaches to Understanding Interactions of Aromatics".In Johnson DW, Hof F (eds.).Aromatic Interactions: Frontiers in Knowledge and Application.England: Royal Society of Chemistry. pp. 1–17.ISBN978-1-78262-662-6.
  14. ^McGaughey GB, Gagné M, Rappé AK (June 1998)."pi-Stacking interactions. Alive and well in proteins".The Journal of Biological Chemistry.273(25): 15458–63.doi:10.1074/jbc.273.25.15458.PMID9624131.
  15. ^Martinez CR, Iverson BL (2012)."Rethinking the term" pi-stacking "".Chemical Science.3(7): 2191.doi:10.1039/c2sc20045g.hdl:2152/41033.ISSN2041-6520.S2CID95789541.
  16. ^Ashton PR, Goodnow TT, Kaifer AE, Reddington MV, Slawin AM, Spencer N, et al. (1989). "A [2] Catenane Made to Order".J. Angew. Chem. Int. Ed.28(10): 1396–1399.doi:10.1002/anie.198913961.
edit
Retrieved from "https://en.wikipedia.org/w/index.php?title=Stacking_(chemistry)&oldid=1249590381"