Synthesis and Characterization of [Yb(NH₃)₈][Cu(S₄)₂]·NH₃, [Yb(NH₃)₈][Ag(S₄)₂]·2NH₃, and [La(NH₃)₉][Cu(S₄)₂] in Supercritical Ammonia:  Metal Sulfide Salts of the First Homoleptic Lanthanide Ammine Complexes

Abstract

Three new lanthanide metal polysulfides have been synthesized in supercritical ammonia: [Yb(NH 3 ) 8 ][Cu(S 4 ) 2 ]· NH 3 ( I ), [Yb(NH 3 ) 8 ][Ag(S 4 ) 2 ]·2NH 3 ( II ), [La(NH 3 ) 9 ][Cu(S 4 ) 2 ] ( III ). Compounds were prepared in sealed quartz tubes which were filled to one-third volume with liquid ammonia and heated at 170 °C for 3 days. Compounds I and II were obtained from the reaction of a premade ytterbium polysulfide with M and S in the ratio of 1:1:4, while [La(NH 3 ) 9 ][Cu(S 4 ) 2 ], III, was obtained by reacting La, Cu, and S in the ratio of 1:1:8. In all these compounds, the lanthanide cation is coordinated only by ammonia, while the M + is chelated by S 4 2 - to form metal tetrasulfide rings. [Yb(NH 3 ) 8 ][Cu(S 4 ) 2 ]·NH 3 and [Yb(NH 3 ) 8 ][Ag(S 4 ) 2 ]·2NH 3 contain [M(S 4 ) 2 ] 3 - anionic units with M + in a distorted tetrahedral coordination environment chelated by two S 4 2 - groups. Compound III, [La(NH 3 ) 9 ][Cu(S 4 ) 2 ], also contains anionic [Cu(S 4 ) 2 ] 3 - units; however, Cu + is in a trigonal planar coordination geometry due to the presence of one monodentate S 4 2 - . All the compounds are unstable with respect to loss of ammonia, and decomposition yielded known ternary and binary phases. Crystallographic data for the compounds are the following: I, space group = I 4̄, Z = 2, a = 10.024(4) Å, c = 9.752(4) Å; II, space group = P 2 1 2 1 2 1, Z = 4, a = 11.177(4) Å, b = 20.472(6) Å, c = 9.754(3) Å; III, space group = P 2 1 / n, Z = 4, a = 9.891(2) Å, b = 12.600(3) Å, c = 17.812(3) Å, β = 103.57(2)°.