Complexes 1-M were prepared by salt metathesis reactions between solvated trivalent metal iodide precursors, [MI3(THF)x] (M = La, Ce, Pr, U, x = 4; M = Nd, x = 3.5), and three equivalents of potassium hypersilanide, [K{Si(SiMe3)3}], in diethyl ether (Scheme 1). Crystalline samples of 1-M were obtained in ca. 40% yields (range = 33-51%) following work-up and recrystallisation from hexane. Microcrystalline 1-M showed nearly superimposable ATR-IR spectra (see Supporting Information Figures ), indicating that they have similar solid-state structures. We consistently obtained low carbon values for 1-M in elemental analyses; we attribute this to incomplete combustion due to silicon carbide formation as this has been postulated for f-block silicon complexes previously, and we note that elemental analysis experiments can be capricious. We therefore interrogated 1-M by powder XRD, and found high phase purity in all cases (see Supporting Information Figures S57-S67 and Table ).