Zintl Phases Foad Tehrani Najafian

Zintl Phases Foad Tehrani Najafian The concept of the ionic compound of main group elements is that one atom gives electron(s) to another atom with the result that both become ions (cation and anion) and both reach an octet (e.g. NaCl). The electronegativity of the constituting elements has a large difference. In covalent compounds the atoms share electrons to reach the octet (e.g. CH4). The electronegativity of the constituting elements is comparable. For a lot of compounds in which the constituting elements have intermediate differences of the electronegativities these two concepts cannot explain the composition and structure. For this compounds Eduard Zintl developed a new concept. What are the Zintl phases? In Zintl phases one element is an electropositive element from the first or second group of the periodic table (alkali or alkaline earth metal), and the second one is a less electropositive element from the groups 13-15. The more electro negativity partner in the Zintl phase’s gets a certain number of electrons from the electropositive one. To reach the octet rule polyanions are formed. Depending on the VEC (see below) the electronegative partner behaves as an element of another group of the periodic table. This means that the anionic structure is related to the structure of an element of this group. What means the VEC? VEC is the valence electrons concentration of the anions in the Zintl phase compounds We can determine the VEC as follows: VEC =(m× e(M) + n× e(A))/n e(M), e(A) are the number of valence electrons of the constituting elements m is the number of the cations, n the number of anions per formula VEC is a very important value for us to determine the group to which the anion belongs. We can use the VEC to calculate the number of covalent bonds of the anions: b(AA) =8-VEC These two values can give us an idea about the Zintl phase compound structure. Examples: NaTl: VEC(Tl) = m × e(M) + n × e(A)/n = (1 × 1 + 1 × 3)/1 = 4 (Tl- behaves like an element of group 14 and forms a diamond-like structure) b(Tl) = 8 - 4 = 4 (that mean that every Tl has 4 covalent bonds) . Be3Si4: VEC (Be3Si4) = (3 × 2 + 4 × 4)/4 = 22/4 = 11/2 b(Be3Si4) = 8 - 11/2 = 5/2 This average value of 2,5 covalent bonds per Si atoms results when half of the Si atoms have 6- 3 covalent bonds and the other 2 have just 2 covalent bonds (the famous “butterfly ion” (Si4) is formed. Properties: • Most Zintl-phase compounds are brittle deeply colored. • They are semiconductors. • They are very sensitive against water and oxygen. • They have a fixed composition. Syntheses: The Zintl phase compounds are typically synthesized by reducing elements of group 13-15 in liquid ammonia in the presence of alkaline or alkaline earth metals. Another possibility is a direct synthesis from elements. Questions: 1) Calculate the VEC for silicon in Na4Si4? Give two possible structure of the anionic part of this Zintl phase. 2) Calculate the VEC for arsenic in CaAs and for germanium in BaGe and propose anionic structures, respectively. .

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Curriculum Vitae Mercouri G
CURRICULUM VITAE MERCOURI G. KANATZIDIS Department of Chemistry, Northwestern University, Evanston, IL 60208 Phone 847-467-1541; Fax 847-491-5937; Website: http://chemgroups.northwestern.edu/kanatzidis/ Birth Date: 1957; Citizenship: US EXPERIENCE 8/06-Present: Professor of Chemistry, Northwestern University and Senior Scientist , Argonne National Laboratory, Materials Science Division, Argonne, IL 7/93-8/06: Professor of Chemistry, Michigan State University 7/91-6/93: Associate Professor, Michigan State University 7/87-6/91: Assistant Professor, Michigan State University EDUCATION Postdoctoral Fellow, 1987, Northwestern University Postdoctoral Associate, 1985, University of Michigan Ph.D. Inorganic Chemistry, 1984, University of Iowa B.S. Chemistry, November 1979, Aristotle University of Thessaloniki AWARDS • Presidential Young Investigator Award, National Science Foundation, 1989-1994 • ACS Inorganic Chemistry Division Award, EXXON Faculty Fellowship in Solid State Chemistry, 1990 • Beckman Young Investigator , 1992-1994 • Alfred P. Sloan Fellow, 1991-1993 • Camille and Henry Dreyfus Teacher Scholar, 1993-1998 • Michigan State University Distinguished Faculty Award, 1998 • Sigma Xi 2000 Senior Meritorious Faculty Award • University Distinguished Professor MSU, 2001 • John Simon Guggenheim Foundation Fellow, 2002 • Alexander von Humboldt Prize, 2003 • Morley Medal, American Chemical Society, Cleveland Section, 2003 • Charles E. and Emma H. Morrison Professor, Northwestern University, 2006 • MRS Fellow, Materials Research Society, 2010 • AAAS Fellow, American Association for the Advancment of Science, 2012 • Chetham Lecturer Award, University of California Santa Barbara, 2013 • Einstein Professor, Chinese Academy of Sciences, 2014 • International Thermoelectric Society Outstanding Achievement Award 2014 • MRS Medal 2014 • Royal Chemical Society DeGennes Prize 2015 • Elected Fellow of the Royal Chemical Society 2015 • ENI Award for the "Renewable Energy Prize" category • ACS Award in Inorganic Chemistry 2016 • American Physical Society 2016 James C.
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Page 1 of Journal7 Name Physical Chemistry Chemical Physics Dynamic Article Links ►
PCCP Accepted Manuscript This is an Accepted Manuscript, which has been through the Royal Society of Chemistry peer review process and has been accepted for publication. Accepted Manuscripts are published online shortly after acceptance, before technical editing, formatting and proof reading. Using this free service, authors can make their results available to the community, in citable form, before we publish the edited article. We will replace this Accepted Manuscript with the edited and formatted Advance Article as soon as it is available. You can find more information about Accepted Manuscripts in the Information for Authors. Please note that technical editing may introduce minor changes to the text and/or graphics, which may alter content. The journal’s standard Terms & Conditions and the Ethical guidelines still apply. In no event shall the Royal Society of Chemistry be held responsible for any errors or omissions in this Accepted Manuscript or any consequences arising from the use of any information it contains. www.rsc.org/pccp Page 1 of Journal7 Name Physical Chemistry Chemical Physics Dynamic Article Links ► Cite this: DOI: 10.1039/c0xx00000x www.rsc.org/xxxxxx ARTICLE TYPE 18-electron rule inspired Zintl-like ions composed of all transition metals Jian Zhou,a Santanab Giri a and Purusottam Jena *,a Manuscript Received (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX 5 DOI: 10.1039/b000000x Zintl phase constitutes a unique class of compounds composed of metal cations and covalently bonded multiply charged cluster anions. Potential applications of these materials in solution chemistry and thermoelectric materials have given rise to renewed interest in the search of new Zintl ions.
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