AbstractDuring attempts to synthesize La3PTe3, after participation of the SiO2‐container material, two so far unknown compounds could be isolated, which both follow the Zintl‐Klemm concept. The novel quaternary lanthanum tellurides La11Si11P21Te5 and La20.667Si18P46Te11.333 crystallize hexagonally in the non‐centrosymmetric space group P c with the unit‐cell parameters a=1204.97(6) pm and c=1802.38(9) pm (c/a=1.496) or a=1205.78(6) pm and c=1802.16(9) pm (c/a=1.495), respectively. Their very similar crystal structures can be divided into two interpenetrating three‐dimensional sublattices, {[La11Te5]23+} (d(La3+−Te2−)=314–335 pm plus 352 pm) and {[Si11P21]23−} (d(Si−P)=221–225 pm, (d(Si−Si)=230–231 pm, (d(P−P)=220–221 pm) for La11Si11P21Te5 (Z=2), displaying unique structural features as compared to related compounds. The linkage of these two sublattices occurs through attractive La3+−Si− and La3+−P− interactions (d(La−Si)=333 pm, (d(La−P)=298–318 pm). For La20.667Si18P46Te11.333 (Z=1), 4/3 out of 22 La3+cations in the doubled formula La22Si22P42Te10 have to be omitted, while the four Si− anions need to be replaced with phosphorus atoms. The La3+ vacancies are filled up with tellurium, partly forming [Te2]2− dumbbells (d(Te−Te)=274 pm). La11Si11P21Te5 can be obtained on target by reacting the elements (La, Si, P and Te) in their respective amounts with an excess of potassium chloride as fluxing agent in evacuated and torch‐sealed glassy silica ampoules for four days at 900 °C as black pillars or thick plates with hexagonal cross‐section.
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