Relativistic Influences in Chemistry

The influence of relativity on chemical bonding leads to the formation of compounds with unexpected properties. For example, by combining two metallic elements, cesium and gold, an intermetallic, CsAu, is formed which is a salt. This appears to be contradictory to the general rule of thumb, that by combining two metals, an intermetallic with metallic properties is obtained. But the unusual properties of CsAu result from the influence of relativity on the valence electrons of Cs and Au. In fact, for a long time it was thought that relativity has little if no influence on the chemistry of the elements. Even Dirac himself, who laid the foundations of relativistic quantum theory, claimed in 1929 that relativistic effects are “of no importance in the consideration of atomic and molecular structure and ordinary chemical reactions.” It was 50 years later that Pyykkö, Desclaux and Pitzer pointed out the special importance of relativity for the chemistry of heavy elements. Over the past years, the foundations for a thorough theoretical treatment of relativistic effects in chemistry have been laid. This helped to understand the origin of peculiar properties of elements and compounds like, for example, the low melting point of mercury. However, the experimental work is still lacking when regarded with the developments in theoretical chemistry. Except for gold, no extended systematic studies are available for other 6th row elements, albeit interesting observations of unusual compounds and bonding states have been made. In order to close the gap between theory and experiment, we conduct systematic experimental studies onto other heavy elements (other than, but sometimes including, gold) to evaluate the impact of relativity and its frontiers in chemistry and get a thorough understanding. This work should lead to a more general understanding how relativity affects chemistry. One recent example includes the synthesis of the first double salt with a true Pt2- anion.

Crystal structure of Cs9Pt4H. Photos of crystalline Cs2Pt and Cs9Pt4H.



“Relativistic Effects in Chemistry”,

Carl-Tryggers Stiftelse för Vetenskaplig Forskning, CTS 18:268, PI, 2019-2021



“Innovative and Complex Metal-Rich Materials”, U.S. Department of Energy,

FWP – AL-08-510-003, co-PI, 2015-2017


“The lone pair effect in heavier element (6th row) compounds”,

GIF – German-Israeli Foundation for Scientific Research and Development,

No. G-2112-1480.5/2005, PI, 2006-2008


“Chemistry with Relativity: Einflüsse relativistischer Effekte auf die Chemie schwerer Elemente“, DFG – Deutsche Forschungsgemeinschaft (Germany),

# 5445587, PI, 2004-2013


Reviews and Book Chapters

R6. V. Smetana, M. Rhodehouse, G. Meyer, A.-V. Mudring, Gold Polar Intermetallics: The Influence of Relativity on Structural Versatility and Exclusive Bonding Motifs, Acc. Chem. Res. 2017, 50, 2633-2641. DOI: 10.1021/acs.accounts.7b00316

B5. A.-V. Mudring: Stereochemical activity of lone pairs in heavier main group elements, in: G. Meyer, D. Naumann, L. Wesemann (Eds.), Inorganic Chemistry in Focus III, Wiley VCH, Chapter 2, p. 15-28 (2006).

B1. M. Jansen, A.-V. Mudring: The Chemistry of Gold Oxides, in: H. Schmidbaur (Ed.), Gold ‑ Progress in Chemistry, Biochemistry and Technology, Wiley, Chichester, p. 747-793 (1999).

Original, peer-reviewed research publications:

  1. V. Smetana, S. Steinberg, A.-V. Mudring, Layered Structures and Disordered Polyanionic Nets in the Cation-Poor Polar Intermetallics CsAu1.4Ga2.8 and CsAu2Ga2.6, Crystal Growth Des. 2017, 17, 693-700. DOI: 10.1021/acs.cgd.6b01536.
  2. V. Smetana, A.-V. Mudring, Cesium Platinide Hydride Cs9Pt4H ≡ 4Cs2Pt·CsH: An Intermetallic Double Salt Featuring Metal Anions, Angew. Chem. Int. Ed. 2016, 47, 14838-14841. DOI:10.1002/anie.201606682. Cover Image. DOI: 10.1002/anie.201609985
  3. A. Provino, S. Steinberg, V. Smetana, U. Paramanik, P. Manfrinetti, S.K. Dhar, A.-V. Mudring, Gold in the Layered Structures of R3Au7Sn3: From Relativity to Versatility, Crystal Growth Des. 2016, 16, 5657-5668. DOI: 10.1021/acs.cgd.6b00478
  4. S. Steinberg, N. Card, A.-V. Mudring, From the Ternary Eu(Au/In)2 and EuAu4(Au/In)2 with Remarkable Au/In Colorings to a New Structure Type: The Gold-rich Eu5Au16(Au,In)6 Structure, Inorg. Chem. 2015, 54, 8187-8196. DOI: 10.1021/acs.inorgchem.5b00257.
  5. A. Provino, S. Steinberg, V. Smetana, R. Kulkarni, S.K. Dhar, P. Manfrinetti, A.-V. Mudring, The Polar Intermetallics Y3Au7Sn3 and Gd3Au7Sn3: Novel Au@Au6 Clusters, Remarkable Physical Properties and Chemical Bonding, J. Mat. Chem. C 2015, 3, 8311-8321. DOI:10.1039/ C5TC00884K. Cover Image.
  6. V. Smetana, S. Steinberg, N. Card A.-V. Mudring, G. Miller, Crystal Structure and Bonding in BaAu5Ga2 and AeAu4+xGa3-​x (Ae = Ba and Eu)​: Hexagonal Diamond-​Type Au Frameworks and Remarkable Cation​/Anion Partitioning in the Ae-​Au-​Ga Systems, Inorg. Chem. 2015, 54, 1010-1018. DOI:10.1021/ic502402y.
  7. F. Rieger, -V. Mudring: Pb(18-crown-6)Cl2 and Hg(18-crown-6)I2: Molecular Dihalides Trapped in a Crown Ether, Z. Anorg. Allg.Chem., 2008, 634, 2989-2993. DOI: 10.1002/ zaac.200800365.
  8. F. Rieger, A.-V. Mudring: Phase transition in Tl2TeO3: influence and origin of the thallium lone pair distortion, Chem., 2007, 46, 446-452. DOI: 10.1021/ic061273j
  9. A.-V. Mudring: Thallium Halides – New Aspects of the Stereochemical Activity of Electron Lone Pairs of Heavier Main-Group Elements, Eur. J. Inorg. Chem., 2007, 882. 10.1002/ejic.200600975.
  10. F. Rieger, A.-V. Mudring: Inorganic Supramolecular Host Architectures:  [(M@18c6)2][TlI4]·2H2O, M = 0.5 Tl, (NH4,NH3), (H3O,H2O), Inorg. Chem., 2005, 44, 9340-9346.
  11. A.-V. Mudring, F. Rieger: Lone Pair Effect in Thallium(I) Macrocyclic Compounds, Inorg.Chem., 2005, 44, 6240-6243. DOI: 10.1021/ic050547k.
  12. A.-V. Mudring, M. Jansen, J. Daniels, S. Krämer, M. Mehring, J.-P. Ramalho, A.-H. Romero, M. Parrinello: Cesiumauride Ammonia (1/1), CsAu⋅NH3: A Crystalline Analogue to Alkali Metals Dissolved in Ammonia?, Angew. Chem. Int. Ed., 2002, 114, 128-132. DOI: 10.1002/1521-3757(20020104)114:1<128::AID-ANGE128>3.0.CO;2-U
  13. 2. -V. Mudring, M. Jansen: Base-induced disproportionation of elemental gold, Angew. Chem. Int. Ed. Engl. 2000, 39, 3066-3067. DOI: 10.1002/1521-3773(20000901)39:17<3066::AID-ANIE3066>3.0.CO;2-J
  14. A.-V. Mudring, J. Nuss, U. Wedig, M. Jansen: Mixed Valent Gold Oxides: Syntheses, Structures, and Properties of Rb5Au3O2, Rb7Au5O2 and Cs7Au5O2, J. Solid State Chem. 2000, 155, 29-36.