Single-Crystal Growth and Size Control of Three Novel Polar Intermetallics: Eu_2.94(2)Ca_6.06In₈Ge₈, Eu_3.13(2)Ca_5.87In₈Ge₈, and Sr_3.23(3)Ca_5.77In₈Ge₈ with Crystal Structure, Chemical Bonding, and Magnetism Studies

Abstract

Three new quaternary polar intermetallic compounds of Eu2.94(2)Ca6.06In8Ge8, Eu3.13(2)Ca5.87In8Ge8, and Sr3.23(3)Ca5.77In8Ge8 have been synthesized by a metal-flux method using molten indium metal as a reactive flux, and the novel isotypic crystal structures have been characterized by both powder and single-crystal X-ray diffractions. All compounds crystallize in the orthorhombic space group Pmmn (Z = 2, Pearson symbol oP50) with 14 crystallographically unique atomic positions in the asymmetric unit. The lattice parameters are refined as follows: a = 36.928(2) Å, b = 4.511(1) Å, and c = 7.506(1) Å for Eu2.94(2)Ca6.06In8Ge8; a = 37.171(19) Å, b = 4.531(2) Å, and c = 7.560(4) Å for Eu3.13(2)Ca5.87In8Ge8; and a = 37.350(2) Å, b = 4.550(3) Å, and c = 7.593(4) Å for Sr3.23(3)Ca5.77In8Ge8. In particular, single crystals of two Eu-containing compounds are obtained as bundles of bar/needle-shaped crystals, and the thicknesses of those crystals can be controlled in the range between ca. 300 μm and ca. <10 μm by adjusting several reaction conditions, including the reaction cooling rate and the centrifugation temperature. The overall crystal structure is illustrated as an assembly of (1) the three-dimensional anionic framework, which is formed by the chains of edge-sharing InGe4 tetrahedra and the annulene-like "12-membered anionic rings" connected via Ge2 dimers, and (2) the cationic mixed sites embedded in the space between the anionic frameworks. Theoretical investigations based on tight-binding linear muffin-tin orbital (TB-LMTO) calculations provide a comprehesive understanding of the overall electronic structure and chemical bonding observed among anionic components and between anions and cations. Electron localization function (ELF) and electron density map present chemical bond strengths and polarization within the anionic framework. Magnetic susceptibility measurement proves an antiferromagnetic (AFM) ordering of Eu atoms below 4 K with a reduced effective magnetic moment of 7.12 μB for the Eu atom.

Experimental and theoretical investigations for site preference and anisotropic size change of RE11Ge4In6−xMx (RE=La, Ce; M=Li, Ge; x=1, 1.96)

“…In and Li at the dumbbell-site based on the coloring concept [26][27][28][29] and conducted a series of calculation to find which short-range local ordering would be energetically the most favorable one.…”

“…For Ce 11 Ge 5.96(3) In 4.04 , we have designed seven model structures based on the coloring problem [26][27][28][29] and performed a series of theoretical calculations (Fig. 7).…”

“…In particular, the site preference between Ge and In on the anionic framework of Ce 11 Ge 5.76(3) In 4.04 was investigated using QVAL values [25]. In addition, the local short-range ordering between anionic elements was suggested by the electronic energy comparison of various structural models which were built based on the "coloring concept" [26][27][28][29]. The partial and total DOS as well as crystal orbital Hamilton population (COHP) analyses [30] were also presented to evaluate atomic orbital interactions influencing the local coordination geometry and chemical bonding among components.…”

Ce11Ge3.73(2)In6.27: Solid-state synthesis, crystal structure and site-preference

“…Moreover, two COHP curves of Ce-Ge1 (8j site) and Ce-Ge2 (4d site) displayed their bonding characters in the relatively lower energy region than that of Ce-In (4e site), which should be attributed to the electronegativity difference between Ge and In. The electron localization function (ELF) [20][21][22] has been evaluated for Ce 11 Ge 3 In 7 (Model 1) to visualize the locations of paired-electron densities along the 3-D anionic framework, and the resultant diagram is displayed in Fig. 4.…”

“…Total and partial densities of states (DOS) curves were studied to elucidate orbital contributions of each component to the electronic structure over whole energy window. Crystal orbital Hamilton population (COHP) curves [19] and the electron localization function (ELF) diagram [20][21][22] were interrogated to understand chemical bonding and paired-electron densities, and magnetic property was also investigated for the title compound.…”