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2,2′-Bipyridine (bipy or bpy, pronounced /ˈbɪp/) is an organic compound with the formula C10H8N2. This colorless solid is an important isomer of the bipyridine family. It is a bidentate chelating ligand, forming complexes with many transition metals. Ruthenium complex and platinum complexes of bipy exhibit intense luminescence, which may have practical applications.

2,2′-Bipyridine
Skeletal formula of 2,2′-bipyridine
Ball-and-stick model of the 2,2′-bipyridine molecule
2,2'-bipyridine sample.jpg
Names
Preferred IUPAC name
2,2'-Bipyridine
Other names
Bipyridyl
Dipyridyl
Bipy
Bpy
Dipy
Identifiers
3D model (JSmol)
113089
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard 100.006.069
EC Number 206-674-4 923-456-0
3720 936807
RTECS number DW1750000
UNII
Properties
C10H8N2
Molar mass 156.188 g·mol−1
Melting point 70 to 73 °C (158 to 163 °F; 343 to 346 K)
Boiling point 273 °C (523 °F; 546 K)
Structure
0 D
Hazards
Main hazards toxic
GHS pictograms The skull-and-crossbones pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS)The exclamation-mark pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS)
GHS signal word Danger
H301, H302, H311, H312, H319, H412
P264, P270, P273, P280, P301+310, P301+312, P302+352, P305+351+338, P312, P321, P322, P330, P337+313, P361, P363, P405, P501
Related compounds
Related compounds
4,4′-Bipyridine
Pyridine
Phenanthroline
3-Pyridylnicotinamide
Terpyridine
Biphenyl
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Contents

Preparation, structure, and general propertiesEdit

It is prepared by the dehydrogenation of pyridine using Raney nickel:[1]

2C5H5N → (C5H4N)2 + H2

Although uncoordinated bipyridine is often drawn with its nitrogen atoms in cis conformation, the lowest energy conformation both in solid state and in solution is in fact coplanar, with nitrogen atoms in trans position.[2] Protonated bipyridine adopts a cis conformation.[3]

Upon complexation, the related N,N-heterocyclic ligand phenanthroline does not incur an enthalpic and entropic penalty, and thus its complexes tend to be more stable. With respective pKa's of 4.86 and 4.3 for their conjugate acids, phenantholine and bipy are of comparable basicity.[4]

Reflecting the popularity of this ligand design, many substituted variants of bipy have been described.[5][6]

Coordination chemistryEdit

Illustrative complexesEdit

Tris-bipy complexesEdit

Bipyridine complexes absorb intensely in the visible part of the spectrum. The electronic transitions are attributed to metal-to-ligand charge transfer (MLCT). In the "tris(bipy) complexes" three bipyridine molecules coordinate to a metal ion, written as [M(bipy)3]n+ (M = metal ion; Cr, Fe, Co, Ru, Rh and so on; bipy = 2,2′-bipyridine). These complexes have six-coordinated, octahedral structures and two enantiomers as follows:

 
 
Three-dimensional view of the [Fe(bipy)3]2+ complex.

These and other homoleptic tris-2,2′-bipy complexes of many transition metals are electroactive. Often, both the metal centred and ligand centred electrochemical reactions are reversible one-electron reactions that can be observed by cyclic voltammetry. Under strongly reducing conditions, most tris(bipy) complexes can be reduced to neutral derivatives containing bipy ligands. Examples include M(bipy)3, where M = Al, Cr, Si.

ReferencesEdit

  1. ^ Sasse, W. H. F. (1966). "2,2′-Bipyridine". Organic Syntheses. 46: 5.; Collective Volume, 5, p. 102
  2. ^ Merritt, L. L.; Schroeder, E. (1956). "The Crystal Structure of 2,2′-Bipyridine". Acta Crystallographica. 9 (10): 801–804. doi:10.1107/S0365110X56002175.
  3. ^ Göller, A.; Grummt, U.-W. (2000). "Torsional barriers in biphenyl, 2,2′-bipyridine and 2-phenylpyridine". Chemical Physics Letters. 321 (5–6): 399–405. doi:10.1016/S0009-2614(00)00352-3.
  4. ^ J. G. Leipoldt, G. J. Lamprecht, E. C.Steynberg (1991). "Kinetics of the substitution of acetylacetone in acetylactonato-1,5-cyclooctadienerhodium(I) by derivatives of 1,10-phenantrholine and 2,2′-dipyridyl". Journal of Organometallic Chemistry. 402: 259–263. doi:10.1016/0022-328X(91)83069-G.CS1 maint: Uses authors parameter (link)
  5. ^ Smith, A. P.; Lamba, J. J. S.; Fraser, C. L. (2002). "Efficient Synthesis of Halomethyl-2,2′-Bipyridines: 4,4′-Bis(chloromethyl)-2,2′-Bipyridine". Organic Syntheses. 78: 82.; Collective Volume, 10, p. 107
  6. ^ Smith, A. P.; Savage, S. A.; Love, J.; Fraser, C. L. (2002). "Synthesis of 4-, 5-, and 6-Methyl-2,2′-Bipyridine by a Negishi Cross-Coupling Strategy". Organic Syntheses. 78: 51.; Collective Volume, 10, p. 517
  7. ^ Lay, P. A.; Sargeson, A. M.; Taube, H.; Chou, M. H.; Creutz, C. (1986). "Cis-Bis(2,2′-Bipyridine-N,N′) Complexes of Ruthenium(III)/(II) and Osmium(III)/(II)". Inorganic Syntheses. 24: 291–299. doi:10.1002/9780470132555.ch78.