Crystal structure and chemical bonding of the intermetallic Zintl phase Yb11AlSb9

High resolution single crystal synchrotron X-ray diffraction data measured at 15(2) K were used to solve the structure of the complex intermetallic Zintl phase, Yb11AlSb9 (space group Iba2), made up of Yb cations and polyanions along with isolated Sb anions. The 15(2) K cell parameters are a = 11.7383(4) angstrom, b = 12.3600(4) angstrom, c = 16.6796(6) angstrom. The temperature dependence of the structure was investigated through high resolution synchrotron powder X-ray diffraction (PXRD) data measured from 90 K to 1000 K. Rietveld refinements of the crystal structure revealed near linear thermal expansion of Yb11AlSb9 with expansion coefficients of 1.49(2) x 10(-5) K-1, 1.71(3) x 10(-5) K-1, 1.13(1) x 10(-5) K-1 for a, b and c, respectively. The chemical bonding in Yb11AlSb9 was analyzed using atomic Hirshfeld surfaces, and the analysis supports the presence of the structural elements of Yb cations, [AlSb4](9-) tetrahedra, [Sb-2](4-) dimers and isolated Sb3- anions. However, indications of interatomic interactions between the Zintl anions and the Yb cations were also observed.