Magnesium-rich intermetallic compounds RE${}_3$Ag${}_4$Mg${}_{12}$ (RE = Y, La-Nd, Sm-Dy, Yb) and AE${}_3$Ag${}_4$Mg${}_{12}$ (AE = Ca, Sr)

The magnesium-rich intermetallic compounds RE${}_3$Ag${}_4$Mg${}_{12}$ (RE = Y, La-Nd, Sm-Dy, Yb) and AE${}_3$Ag${}_4$Mg${}_{12}$ (AE = Ca, Sr) were synthesized from the elements in sealed tantalum ampoules through heat treatment in an induction furnace. X-ray powder diffraction studies confirm the hexagonal Gd${}_3$Ru${}_4$Al${}_{12}$ type structure, space group P6${}_3$/mmc. Three structures were refined from single crystal X-ray diffractometer data: a = 973.47(5), c = 1037.19(5) pm, wR2 = 0.0296, 660 F${}^2$ values, 30 variables for Gd${}_3$Ag${}_{3.82\left(1\right)}$Mg${}_{12.18\left(1\right)}$, a = 985.27(9), c = 1047.34(9) pm, wR2 = 0.0367, 716 F${}^2$ values, 29 variables for Yb${}_3$Ag${}_{3.73\left(1\right)}$Mg${}_{12.27\left(1\right)}$ and a = 992.41(8), c = 1050.41(8) pm, wR2 = 0.0373, 347 F${}^2$ values, 28 variables for Ca${}_3$Ag${}_{3.63\left(1\right)}$Mg${}_{12.37\left(1\right)}$. Refinements of the occupancy parameters revealed substantial Ag/Mg mixing within the silver-magnesium substructure, a consequence of the Ag@Mg${}_8$ coordination. The alkaline earth and rare earth atoms build Kagome networks. Temperature dependent magnetic susceptibility measurements indicate diamagnetism/Pauli paramagnetism for the compounds with Ca, Sr, Y and Yb${}^{II}$, while the others with the trivalent rare earth elements are Curie-Weiss paramagnets. Most compounds order antiferromagnetically at T${}_N$ = 4.4(1) K (RE = Pr), 34.6(1) K (RE = Gd) and 23.5(1) K (RE = Tb) while Eu${}_3$Ag${}_4$Mg${}_{12}$ is a ferromagnet (T${}_C$ = 19.1(1) K). ${}^{151}$Eu Mössbauer spectra confirm divalent europium (δ = -9.88(1) mm s${}^{-1}$). Full magnetic hyperfine field splitting (18.4(1) T) is observed at 6 K. Yb${}_3$Ag${}_4$Mg${}_{12}$ shows a single resonance in its ${}^{171}$Yb solid state NMR spectrum at 6991 ppm at 300 K indicating a strong, positive Knight shift.