The True Nature of SmSb₂O₄Cl: Syntheses and Crystal Structures of Sm₂[Sb₄O₈]Cl₂ and Eu₂[Sb₄O₈]Cl₂

Abstract

Dedicated to Professor Caroline Röhr on the Occasion of her 60th BirthdayThe two lanthanoid oxidoantimonate (III) chlorides SmSb 2 O 4 Cl and EuSb 2 O 4 Cl are accessible from solid-state reactions of Sb 2 O 3 with Ln 2 O 3 and LnCl 3 (Ln = Sm and Eu) at 750 °C for two days. They crystallize in the centrosymmetric tetragonal space group P4/ncc with the lattice parameters a = 787.13(4) pm, c = 1765.24(12) pm for SmSb 2 O 4 Cl and a = 783.56(4) pm, c = 1764.05(12) pm for EuSb 2 O 4 Cl with Z = 8. Both can also be described with the crystal-chemical formula Ln 2 [Sb 4 O 8 ]Cl 2 for Z = 4, since they comprise isolated [Sb 4 O 8 ] 4À rings. This structural motif has some very close similarities to the known series of non-centrosymmetric LnSb 2 O 4 Cl representatives (Ln = Gd-Lu), crystallizing in the tetragonal space group P42 1 2. All lanthanoid(III) cations have eight oxygen atoms as nearest neighbors arranged as square prisms [LnO 8 ] 13À , which are connected to layers by four parallel edges according to 2 ∞ f½LnO e8=2 � 5À g with fluorite-like topology. The Sb 3 + cations together with three oxygen atoms each and their lone-pair of electrons form ψ 1 -tetrahedra [SbO 3 ] 3À . Four of these [SbO 3 ] 3À entities join to 0 ∞ Sb 4 O 8 ½ � 4À f g rings with four bridging and four terminal oxygen atoms. Both centrosymmetric representatives, in contrast to the series of non-centrosymmetric ones, have a doubled lattice parameter c and several more symmetry elements, which will be discussed in detail.

Three New Lanthanum Oxoantimonate(III) Halides: Synthesis and Crystal Structure of La5Cl3[SbO3]4, La2Sb12O19Br4 and La2Sb12O19I4

“…The Raman spectrum of La 2 Sb 12 O 19 I 4 , shown in Figure 16, was recorded at an excitation wavelength of λ = 532 nm. At a wavenumber of 627 cm −1 , the push-pull valence vibration can be seen, which is much more pronounced in contrast to the chloride derivatives RESb 2 O 4 Cl (RE = Y, Sm-Lu) [3,6,[12][13][14], while the valence vibration in the common mode can not be detected in the spectrum at all. This is due to the presence of isolated [Sb 4 O 8 ] 4− -ring units consisting of four vertex-connected ψ 1 -tetrahedra [SbO 3 ] Br 4 , endless "double-halfpipes" of antimony and oxygen with mostly tetracoordinated Sb 3+ cations are encountered.…”

“…As with the rare-earth metal(III) oxoantimonate(III) chlorides of composition RESb2O4Cl (RE = Y, Sm-Lu) [3,6,[12][13][14], the common mode valence vibration of the terminal oxygen atoms to the antimony is similarly pronounced at about 700-720 cm −1 . However, La5Cl3[SbO3]4 lacks the push-pull vibration, which is found in the range of 660 cm −1 for GdSb2O4Cl and at 672 cm −1 for SmSb2O4Cl, since the latter contains discrete [Sb4O8] 4− rings of four cyclically vertex-connected ψ 1 -tetrahedral [SbO3] 3− units according to RE2[Sb4O8]Cl2 [3,6,[12][13][14]. [22] and even better with PbFCl-type LaOBr (d(La-O) = 240 pm) [31] and LaOI (d(La-O) = 241 pm) [32] although there are no Xanions in the coordination sphere of La 3+ in the La 2 Sb 12 O 19 X 4 cases.…”

“…Compared to the rare-earth metal(III) bromide oxoarsenates(III) RE 5 Br 3 [AsO 3 ] 4 , the spectrum is almost the same, but the peaks are much better defined and only shifted by a few wavenumbers [29,30]. As with the rare-earth metal(III) oxoantimonate(III) chlorides of composition RESb 2 O 4 Cl (RE = Y, Sm-Lu) [3,6,[12][13][14], the common mode valence vibration of the terminal oxygen atoms to the antimony is similarly pronounced at about 700-720 cm −1 . However, La The symmetric Sb 3+ -O 2− valence vibration can be identified as the second strongest band, which is located at a wavenumber of about 721 cm -1 for La5Cl3[SbO3]4.…”

“…Compared to the rare-earth metal(III) bromide oxoarsenates(III) RE5Br3[AsO3]4, the spectrum is almost the same, but the peaks are much better defined and only shifted by a few wavenumbers [29,30]. As with the rare-earth metal(III) oxoantimonate(III) chlorides of composition RESb2O4Cl (RE = Y, Sm-Lu) [3,6,[12][13][14], the common mode valence vibration of the terminal oxygen atoms to the antimony is similarly pronounced at about 700-720 cm −1 . However, La5Cl3[SbO3]4 lacks the push-pull vibration, which is found in the range of 660 cm −1 for GdSb2O4Cl and at 672 cm −1 for SmSb2O4Cl, since the latter contains discrete [Sb4O8] 4− rings of four cyclically vertex-connected ψ 1 -tetrahedral [SbO3] 3− units according to RE2[Sb4O8]Cl2 [3,6,[12][13][14].…”

“…Moreover, the existence of completely different compositions and crystal structures for the tetragonal oxobismuthate(III) halides REBi 2 O 4 X (RE = Y, La, Pr, Nd, Sm-Lu, X = Cl-I) [6,[8][9][10][11], crystallizing in space group P4/mmm, was encouragement enough for more systematic studies. First results on the oxoantimonate(III)-halide branch have revealed that the tetragonal RESb 2 O 4 Cl representatives for RE = Sm and Eu [6,12] crystallize in space group P4/ncc, but for RE = Y, Gd-Lu [3,6,13,14] in space group P42 1 2, whereas the RESb 2 O 4 Br representatives with RE = Y, Eu-Dy [3,6,13,15,16] prefer the monoclinic space group P2 1 /c. All before-mentioned investigations have so far shown that for As 3+ exclusively isolated [AsO 3 ] 3− anions are present as ψ 1 -tetrahedral trigonal pyramids, while for the Sb 3+ case the analogous units [SbO 3 ] 3aspire to an extra oxygen contact for their central Pn 3+ cation, which becomes a general feature in the oxobismuthate(III) halides, where vertex-sharing [BiO 4 ] 5− units dominate as ψ 1 ax -square pyramids for the heaviest Pn 3+ congener.…”