Sr${}_4$Pt${}_{10}$In${}_{21}$. The first representative of the Ho${}_4$Ni${}_{10}$In${}_{21}$ type with a divalent cation

Rod-shaped single crystals of Sr${}_4$Pt${}_{10}$In${}_{21}$ were prepared from the elements in glassy-carbon crucibles in a high-frequency furnace. The structure of Sr${}_4$Pt${}_{10}$In${}_{21}$ was refined from single-crystal X-ray diffractometer data: C2/m, Ho${}_4$Ni${}_{10}$In${}_{21}$ type, a = 2322.62(7), b = 450.27(2), c = 1958.09(7) pm, $\beta$ = 133.191(3)°, wR = 0.0464, 3200 F${}^2$ values and 107 variables. The three-dimensional [Pt${}_{10}$In${}_{21}$]${}^{\delta \text{â}\text{ˆ}\text{’}}$ polyanionic network is stabilized through substantial Pt–In (269–313 pm Pt–In) and In–In (294–362 pm In–In) bonding. All platinum atoms have slightly distorted tri-capped trigonal prismatic coordination and the two crystallographically independent strontium atoms are located in penta-capped pentagonal prisms.