18-Electron rule inspired Zintl-like ions composed of all transition metals

Abstract

Zintl phase compounds constitute 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 for new Zintl ions. Up to now these ions have been mostly composed of group 13, 14, and 15 post-transition metal elements and no Zintl ions composed of all transition metal elements are known. Using gradient corrected density functional theory we show that the 18-electron rule can be applied to design a new class of Zintl-like ions composed of all transition metal atoms. We demonstrate this possibility by using Ti@Au12(2-) and Ni@Au6(2-) di-anions as examples of Zintl-like ions. Predictive capability of our approach is demonstrated by showing that FeH6(4-) in an already synthesized complex metal hydride, Mg2FeH6, is a Zintl-like ion, satisfying the 18-electron rule. We also show that novel Zintl phase compounds can be formed by using all transition metal Zintl-like ions as building blocks. For example, a two-dimensional periodic structure of Na2[Ti@Au12] is semiconducting and nonmagnetic while a one-dimensional periodic structure of Mg[Ti@Au12] is metallic and ferromagnetic. Our results open the door to the design and synthesis of a new class of Zintl-like ions and compounds with potential for applications.

Endohedrally Doped Cage Clusters

“…Besides the silicon and germanium based 1D nanostructures inspired by the endohedrally doped cage clusters, there have been a few theoretical designs of 1D nanotubes or nanowires based on doped Au 12 cage clusters. Using Mg[Ti@Au 12 ] clusters that fulfill the 18-electron rule as building blocks, J. Zhou et al 902 proposed a 1D periodic Zintl-like phase of Mg[Ti@Au 12 ], which is a ferromagnetic metal with each Ti atom carrying a magnetic moment of 2.13 μ B . Recently, Yong et al 903 have constructed an ultrathin W−Au alloy nanowire by assembling icosahedral W@ Au 12 clusters (which have been discussed in Section 7.1.1), as shown in Figure 104.…”

“…These insights pave a new way to achieve 2D silicon-based spintronic materials. Following the 18-electron rule and using Na 2 [Ti@Au 12 ] clusters as building blocks, J. Zhou et al 902 designed a 2D periodic Zintl-like phase of Na 2 [Ti@Au 12 ] (Figure 109a), which is a semiconductor with an indirect band gap of 0.55 eV using PBE functional as can be seen from the band structure shown in Figure 109b. Bader charge analysis revealed that each Na atom donates about 0.77 electrons to the Ti@Au 12 moiety, confirming its Zintl-like character.…”

“…(a) Relaxed geometry (belonging to the P4/mm plane symmetry group) and (b) band structure of 2D Na 2 [Ti@Au 12 ] along high symmetry directions: Γ­(0,0,0) to X­(1/2,0,0), then to M­(1/2,1/2,0), and finally to Γ. Reproduced with permission from ref . Copyright 2014 Royal Society of Chemistry.…”

Noble Gas Encapsulated Endohedral Zintl Ions Ng@Pb122–and Ng@Sn122–(Ng = He, Ne, Ar, and Kr): A Theoretical Investigation

“…. 26−28 Zintl-like ions composed of only transition metal atoms such as [Ni@Au 6 ] 2− and [Ti@Au 12 ] 2− have also been proposed recently 81 on the basis of the 18electron rule. All of these aspects have motivated us to explore the stability of noble gas encapsulated Pb 12 2− and Sn 12 2− clusters.…”

“…A highly stable 32-electron system of Pu@Pb 12 and other actinide encapsulated Pb 12 2– , clusters have also been investigated. In contrast to M@Au 12 and encapsulated Ge and Si clusters where dopants are critical in stabilizing cage structures, − M@Pb 12 and M@Sn 12 derive stability from the intrinsic stability of parent clusters, Pb 12 2– and Sn 12 2– , due to their greater aromaticity as compared to Ge 12 2– . − Zintl-like ions composed of only transition metal atoms such as [Ni@Au 6 ] 2– and [Ti@Au 12 ] 2– have also been proposed recently on the basis of the 18-electron rule. All of these aspects have motivated us to explore the stability of noble gas encapsulated Pb 12 2– and Sn 12 2– clusters.…”