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Zintl phase

In chemistry, a Zintl phase is the product of a reaction between a group 1 (alkali metal) or group 2 (alkaline earth) and any post-transition metal or metalloid (i.e. from group 13, 14, 15 or 16). It is named after the German chemist Eduard Zintl who investigated them in the 1930s, with the term "Zintl Phases" first used by Laves in 1941.

Zintl phases are a subgroup of brittle, high-melting intermetallic compounds which are diamagnetic or exhibit temperature-independent paramagnetism, and are poor conductors or semiconductors. Zintl noted that there was an atomic volume contraction when these compounds were formed and realised this could indicate cation formation. He suggested that the structures of Zintl phases were ionic, where there was complete electron transfer from the more electropositive metal. The structure of the anion (nowadays called the Zintl ion) should then be considered on the basis of the resulting electronic state. These ideas were further developed to become the Zintl rule or Zintl Klemm concept, where the polyanion structure should be similar to an isoelectronic element.

Contents

Zintl phases are polyanionic compounds. Their structure can be understood by a formal electron transfer from the electropositive metal to the more electronegative element. Thus, the valence-electron concentration (VEC) of the element is increased and it formally moves to the right in the periodic system of elements. Generally, the formed anion does not reach an electron-octet. To compensate the lack of electrons, element-element bonds are formed. The structure can be explained by the 8-N rule (replacing the number of valence electrons N by VEC) and is thus similar to an iso-valence electronic element. The formed polyanions can be chains (one-dimensional), two- or three-dimensional networks or molecule-like entities (i.e. Si44--tetrahedra in KSi).

Zintl ions

Zintl phases that contain molecule-like polyanions are often soluble in liquid-ammonia, ethylenediamine, crown ethers or cryptand solutions. Therefore, they are referred to as (naked) Zintl ions. While extended networks are typical for electron rich anions, the isolated species are often found on the more electron poor side. The structures do not resemble pseudo-elemental configurations but can be described as clusters by Wade's rules.

Structure of [As7]3- subunit in the Zintl phase Cs2NaAs7.
Diamondoid framework of Tl ions in NaTl.

• NaTl consists of a polyanion (—Tl—)n with a covalent diamond structure. Na+ ions are located between the anions. Concept: Tl ~ C.

• NaSi: the polyanion is tetrahedral (Si4)4−, similar to P4. Concept: Si ~ P.

• Na2Tl: the polyanion is tetrahedral (Tl4)8−, similar to P4. Concept: Tl2- ~ P.

• Cs2NaAs7: the trianion adopts the structure of P4S3. Concept: As ~ S.

• K12Si17: there are two types of Zintl ions: 2x Si44- (pseudo P4, or according to Wade's rules, 12 = 2n + 4 skeletal-electrons corresponding to a nido-form of a trigonal-bipyramid) and 1x Si94- (according to Wade's rules, 22 = 2n + 4 skeletal-electrons corresponding to a nido-form of a bicapped square-antiprims)

The Zintl line is a hypothetical boundary drawn between group 13 and group 14, to highlight the tendency for group 13 metals to form phases with a variety of stoichiometries, which contrasts to group 14 and above that tend to form salts with polymeric anions. It is now recognised that some Zintl phases contain Zintl clusters and that this accounts for the variable stoichiometries. The bonding in many of these clusters cannot be accounted for by classical octet rule involving covalent, 2-centre, 2-electron bonds, as implied by the Zintl rule. The reaction of Ge, Sn or Pb and Na in liquid NH3 in the presence of ethylene diamine (en) gives the Zintl cluster Na4en7Sn9.

Zintl phases can incorporate hydrogen. Such Zintl phase hydrides can be either formed by direct synthesis of the elements or element hydrides in a hydrogen atmosphere or by a hydrogenation reaction of a pristine Zintl phase. Since Hydrogen has a comparable electronegativity as the post-transition metal it is incorporated as part of the polyanionic spatial structure. There are two structural motifs present. A monatomic hydride can be formed occupying an interstitial site that is coordinated by cations exclusively (Interstitial hydride). Furthermore, hydrogen can bind covalently to the polyanion (polyanionic hydride).

There are examples of a new class of compounds that, on the basis of their chemical formulae, would appear to be Zintl phases, e.g., K8In11, which is metallic and paramagnetic. Molecular orbital calculations have shown that the anion is (In11)7− and that the extra electron is distributed over the cations and, possibly, the anion antibonding orbitals.

  1. S.M. Kauzlarich, Encyclopedia of Inorganic chemistry, 1994, John Wiley & Sons, ISBN 0-471-93620-0
  2. Fässler, Thomas F. (2011). Zintl Phases: Principles and Recent Developments. Structure and Bonding (Berlin). Structure and Bonding. 139. doi:10.1007/978-3-642-21150-8. ISBN 978-3-642-21149-2. ISSN 0081-5993.
  3. Sevov, S.C., Zintl Phases in Intermetallic Compounds, Principles and Practice: Progress, Westbrook, J.H.; *Freisher, R.L.: Eds.; John Wiley & Sons. Ltd., Chichester, England, 2002, pp. 113-132 Slavi Chapter
  4. Schäfer, Herbert; Eisenmann, Brigitte; Müller, Wiking (1973). "Zintl Phases: Transitions between Metallic and Ionic Bonding". Angewandte Chemie International Edition in English. 12 (9): 694–712. doi:10.1002/anie.197306941. ISSN 1521-3773.
  5. He H, Tyson C, Bobev S (2011). "New compounds with (As7)3- Clusters: Synthesis and Crystal Structures of the Zintl Phases Cs2NaAs7, Cs4ZnAs14 and Cs4CdAs14". Crystals. 1 (3): 87–p98. doi:10.3390/cryst1030087.
  6. Cotton, F. Albert; Wilkinson, Geoffrey; Murillo, Carlos A.; Bochmann, Manfred (1999), Advanced Inorganic Chemistry (6th ed.), New York: Wiley-Interscience, ISBN 0-471-19957-5
  7. Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8.
  8. Häussermann U, Kranak VF, Puhakainen K (2010). "Hydrogenous Zintl Phases: Interstitial Versus Polyanionic Hydrides". Zintl Phases. Structure and Bonding. 139. pp. 143–161. doi:10.1007/430_2010_20. ISBN 978-3-642-21149-2. ISSN 0081-5993.
  9. Slavi C. Sevov; John D. Corbett (1991). "A remarkable hypoelectronic indium cluster in K8In11". Inorg. Chem. 30 (26): 4875–4877. doi:10.1021/ic00026a004.

Zintl phase
Zintl phase Language Watch Edit 160 160 Redirected from Zintl phases In chemistry a Zintl phase is the product of a reaction between a group 1 alkali metal or group 2 alkaline earth and any post transition metal or metalloid i e from group 13 14 15 or 16 It is named after the German chemist Eduard Zintl who investigated them in the 1930s 1 with the term Zintl Phases first used by Laves in 1941 2 Zintl phases are a subgroup of brittle high melting intermetallic compounds which are diamagnetic or exhibit temperature independent paramagnetism and are poor conductors or semiconductors 3 Zintl noted that there was an atomic volume contraction when these compounds were formed and realised this could indicate cation formation 3 He suggested that the structures of Zintl phases were ionic where there was complete electron transfer from the more electropositive metal 3 The structure of the anion nowadays called the Zintl ion should then be considered on the basis of the resulting electronic state These ideas were further developed to become the Zintl rule or Zintl Klemm concept where the polyanion structure should be similar to an isoelectronic element 1 Contents 1 Polyanions 1 1 Zintl ions 2 Examples 3 Zintl line 4 Hydrides 5 Exceptions 6 See also 7 References 8 Additional resourcesPolyanions EditZintl phases are polyanionic compounds Their structure can be understood by a formal electron transfer from the electropositive metal to the more electronegative element Thus the valence electron concentration VEC of the element is increased and it formally moves to the right in the periodic system of elements Generally the formed anion does not reach an electron octet To compensate the lack of electrons element element bonds are formed The structure can be explained by the 8 N rule replacing the number of valence electrons N by VEC and is thus similar to an iso valence electronic element 4 The formed polyanions can be chains one dimensional two or three dimensional networks or molecule like entities i e Si44 tetrahedra in KSi Zintl ions Edit Zintl phases that contain molecule like polyanions are often soluble in liquid ammonia ethylenediamine crown ethers or cryptand solutions Therefore they are referred to as naked Zintl ions While extended networks are typical for electron rich anions the isolated species are often found on the more electron poor side The structures do not resemble pseudo elemental configurations but can be described as clusters by Wade s rules Examples Edit Structure of As7 3 subunit in the Zintl phase Cs2NaAs7 5 Diamondoid framework of Tl ions in NaTl NaTl consists of a polyanion Tl n with a covalent diamond structure Na ions are located between the anions Concept Tl C 1 NaSi the polyanion is tetrahedral Si4 4 similar to P4 Concept Si P 1 Na2Tl the polyanion is tetrahedral Tl4 8 similar to P4 Concept Tl2 P 6 Cs2NaAs7 the trianion adopts the structure of P4S3 Concept As S K12Si17 there are two types of Zintl ions 2x Si44 pseudo P4 or according to Wade s rules 12 2n 4 skeletal electrons corresponding to a nido form of a trigonal bipyramid and 1x Si94 according to Wade s rules 22 2n 4 skeletal electrons corresponding to a nido form of a bicapped square antiprims Zintl line EditThe Zintl line is a hypothetical boundary drawn between group 13 and group 14 to highlight the tendency for group 13 metals to form phases with a variety of stoichiometries which contrasts to group 14 and above that tend to form salts with polymeric anions It is now recognised that some Zintl phases contain Zintl clusters and that this accounts for the variable stoichiometries The bonding in many of these clusters cannot be accounted for by classical octet rule involving covalent 2 centre 2 electron bonds as implied by the Zintl rule The reaction of Ge Sn or Pb and Na in liquid NH3 in the presence of ethylene diamine en gives the Zintl cluster Na4en7Sn9 7 Hydrides EditZintl phases can incorporate hydrogen Such Zintl phase hydrides 8 can be either formed by direct synthesis of the elements or element hydrides in a hydrogen atmosphere or by a hydrogenation reaction of a pristine Zintl phase Since Hydrogen has a comparable electronegativity as the post transition metal it is incorporated as part of the polyanionic spatial structure There are two structural motifs present A monatomic hydride can be formed occupying an interstitial site that is coordinated by cations exclusively Interstitial hydride Furthermore hydrogen can bind covalently to the polyanion polyanionic hydride Exceptions EditThere are examples of a new class of compounds that on the basis of their chemical formulae would appear to be Zintl phases e g K8In11 9 which is metallic and paramagnetic Molecular orbital calculations have shown that the anion is In11 7 and that the extra electron is distributed over the cations and possibly the anion antibonding orbitals 9 See also EditPlumbide StannideReferences Edit a b c d S M Kauzlarich Encyclopedia of Inorganic chemistry 1994 John Wiley amp Sons ISBN 0 471 93620 0 Fassler Thomas F 2011 Zintl Phases Principles and Recent Developments Structure and Bonding Berlin Structure and Bonding 139 doi 10 1007 978 3 642 21150 8 ISBN 978 3 642 21149 2 ISSN 0081 5993 a b c Sevov S C Zintl Phases in Intermetallic Compounds Principles and Practice Progress Westbrook J H Freisher R L Eds John Wiley amp Sons Ltd Chichester England 2002 pp 113 132 Slavi Chapter Schafer Herbert Eisenmann Brigitte Muller Wiking 1973 Zintl Phases Transitions between Metallic and Ionic Bonding Angewandte Chemie International Edition in English 12 9 694 712 doi 10 1002 anie 197306941 ISSN 1521 3773 He H Tyson C Bobev S 2011 New compounds with As7 3 Clusters Synthesis and Crystal Structures of the Zintl Phases Cs2NaAs7 Cs4ZnAs14 and Cs4CdAs14 Crystals 1 3 87 p98 doi 10 3390 cryst1030087 Cotton F Albert Wilkinson Geoffrey Murillo Carlos A Bochmann Manfred 1999 Advanced Inorganic Chemistry 6th ed New York Wiley Interscience ISBN 0 471 19957 5 Greenwood Norman N Earnshaw Alan 1997 Chemistry of the Elements 2nd ed Butterworth Heinemann ISBN 978 0 08 037941 8 Haussermann U Kranak VF Puhakainen K 2010 Hydrogenous Zintl Phases Interstitial Versus Polyanionic Hydrides Zintl Phases Structure and Bonding 139 pp 143 161 doi 10 1007 430 2010 20 ISBN 978 3 642 21149 2 ISSN 0081 5993 a b Slavi C Sevov John D Corbett 1991 A remarkable hypoelectronic indium cluster in K8In11 Inorg Chem 30 26 4875 4877 doi 10 1021 ic00026a004 Additional resources EditVideo of preparation of K4Ge9 subscription required Retrieved from https en wikipedia org w index php title Zintl phase amp oldid 1040956400, wikipedia, wiki, book,

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