Zr(11)Sb(18): a new binary antimonide exhibiting an unusual Sb atom network with nonclassical Sb-Sb bonding

The herewith-introduced antimonides Zr(11)Sb(18) and Zr(10.4)V(0.6)Sb(18) were prepared by high-temperature techniques; both arc-melting and solid-state reactions at 1200 degrees C starting from alpha-ZrSb(2) and the metals Zr and V in powder form are possible methods. These isostructural compounds represent an unprecedented metal:antimony ratio of 11:18 and form a new structure type. Zr(11)Sb(18) crystallizes in the tetragonal space group I(-)42d, with the lattice dimensions a = 676.94(4) pm and c = 6007.3(5) pm, while the V-containing phase forms a slightly smaller unit cell with a = 676.48(8) pm and c = 6005.6(9) pm (Z = 4). Their structures are comprised of an Sb atom substructure with several intermediate Sb-Sb bonds starting at 311 pm, which is reminiscent of that found in the series (Ti,M)(5)Sb(8) (M = Zr, Hf, Nb, Mo) published last year. Interwoven with this network is the Zr atom network, which forms a diamond-like metal atom substructure with long Zr-Zr contacts of ca. 360 pm. Band structure calculations based on the linear muffin tin orbital approach reveal these antimonides to be mainly stabilized by strong M-Sb and intermediate Sb-Sb bonds, and additionally--to the smallest extent--by M-M bonds (M = Zr, V). In agreement with the electronic structure calculations, Zr(11)Sb(18) is metallic with a small positive Seebeck coefficient.     

MA(delta)Sb(2-delta) (M = Zr, Hf; A = Si, Ge): a new series of ternary antimonides and not "beta-ZrSb2"

The ternary antimonides ZrSi(delta)Sb(2-delta), HfGe(delta)Sb(2-delta), and ZrGe(delta)Sb(2-delta) were prepared by annealing of the elements in stoichiometric ratios below 800 degrees C. ZrSi(delta)Sb(2-delta) was earlier erroneously described as the binary "beta-ZrSb(2)", which does not exist as such, because the incorporation of tetrel atoms is necessary for the formation of this structure. ZrSi(delta)Sb(2-delta) has a small yet significant phase width with at least 0.066(7) < or = delta < or = 0.115(3), whereas the Ge analogues exist with larger tetrel concentration, i.e., ZrGe(0.211(5))Sb(1.789) and HfGe(0.205(6))Sb(1.795). The whole series of title compounds crystallizes in the Co(2)Si type (space group Pnma), with lattice dimensions of, e.g., for ZrGe(0.211(5))Sb(1.789), a = 730.4(1) pm, b = 395.13(6) pm, c = 957.6(2) pm, V = 0.27635(7) nm(3), Z = 4. The anionic substructure comprises infinite ribbons formed by the atom sites Q1 and Sb2, with Q1 being mixed occupied by Si or Ge and Sb atoms. These ribbons exhibit Q1-Q1 single bonds and Q1-Sb2 "half" bonds. Assuming the validity of the 8 - N rule, one can assign seven valence-electrons to Sb2 but only five to Q1, which might explain the preference of the tetrel atoms for the latter site.     

Electronic structures of M21S8 (M = Nb, Zr) and (M,M')21S8 (M, M' = Hf, Ti; Nb, Ta) phases and reasons for variations in the metal site occupations

The electronic structures of binary M21S8 (M = Nb, Zr) and isostructural ternary (M,M')21S8 (M, M' = Hf, Ti; Nb, Ta) phases have been studied by means of extended Hückel tight-binding band structure calculations. For the valence electron concentration in the binary group 5 metal phase Nb21S8, metal-metal bonding is optimized whereas, in the isostructural group 4 metal phase Zr21S8, metal-metal bonding levels exist above the Fermi level. However, the electronic structure analysis suggests a stable structure for M21S8 phases with group 4 metals and that (M,M')21S8 phases with mixed group 4 and group 5 metals, even if not yet reported, could well exist. In the ternary phase Nb6.9Ta14.1S8, a linear relationship exists between the magnitude of the metal-metal bonding capacity (as expressed by the total metal-metal Mulliken overlap population) of each crystallographically independent metal site and the occupation of the site with the heavier metal (i.e., the element with the greater bonding capability). The situation is quite more complex in Hf7.5Ti13.5S8, where the metal-metal bonding capacity of each site, differences in electronegativity between Ti and Hf, and site volume arguments must be taken into account to understand the metal site occupation.     

Zr(7)Sb(4): a new binary zirconium-rich antimonide

Zr(7)Sb(4) has been prepared by arc-melting of the elemental components and annealing at 1000-1150 degrees C. Its crystal structure was determined by X-ray diffraction (Pearson symbol mP44, monoclinic, space group P2(1)/c, Z = 4, a = 8.4905(6) A, b = 11.1557(8) A, c = 11.1217(8) A, beta = 111.443(2) degrees at 295 K). Zr(7)Sb(4) is isotypic to Hf(6)TiSb(4), a compound stabilized by differential fractional site occupancy. It is the first binary group-4 antimonide with this metal-to-antimony ratio, but it differs from the corresponding phosphides and arsenides M(7)Pn(4) (M = Ti, Zr, Hf; Pn = P, As), which adopt the Nb(7)P(4)-type structure. Zr(7)Sb(4) is built up from layers excised from the tetragonal W(5)Si(3)-type structure; these layers are displaced relative to each other to maximize interlayer Zr-Zr and Zr-Sb bonding, as confirmed by band structure calculations.     

Metal-metal interactions in heterobimetallic d8-d10 complexes. Structures and spectroscopic investigation of [M'M' '(mu-dcpm)2(CN)2]+ (M' = Pt,Pd; M' ' = Cu,Ag, Au) and related complexes by UV-vis absorption and resonance Raman spectroscopy and ab initio calculations

X-ray structural and spectroscopic properties of a series of heterodinuclear d(8)-d(10) metal complexes [M'M' '(mu-dcpm)(2)(CN)(2)](+) containing d(8) Pt(II), Pd(II), or Ni(II) and d(10) Au(I), Ag(I), or Cu(I) ions with a dcpm bridging ligand have been studied (dcpm = bis(dicyclohexylphosphino)methane; M' = Pt, M' ' = Au 4, Ag 5, Cu, 6; M' ' = Au, M' = Pd 7, Ni 8). X-ray crystal analyses showed that the metal...metal distances in these heteronuclear metal complexes are shorter than the sum of van der Waals radii of the M' and M' ' atoms. The UV-vis absorption spectra of 4-6 display red-shifted intense absorption bands from the absorption spectra of the mononuclear trans-[Pt(phosphine)(2)(CN)(2)] and [M' '(phosphine)(2)](+) counterparts, attributable to metal-metal interactions. The resonance Raman spectra confirmed assignments of (1)[nd(sigma)-->(n + 1)p(sigma)] electronic transitions to the absorption bands at 317 and 331 nm in 4 and 6, respectively. The results of theoretical calculations at the MP2 level reveal an attractive interaction energy curve for the skewed [trans-Pt(PH(3))(2)(CN)(2)-Au(PH(3))(2)(+)] dimer. The interaction energy of Pt(II)-Au(I) was calculated to be ca. 0.45 ev.     

The First Titanium Molybdenum Antimonide: Ti5.42Mo2.58Sb9, a Substitution Variant of Zr2V6Sb9

The new ternary antimonide Ti_5.42(2)Mo_2.58Sb₉ was uncovered by a reaction of the elements under exclusion of air at 1150 °C. It crystallizes in a ternary substitution variant of the V_7.5Sb₉ type, a structure not known to exist in either the Ti/Sb or the Mo/Sb system. The crystal structure of Ti_5.42Mo_2.58Sb₉ was determined from single crystal X‐ray data: space group P4/nmm, with a = 9.8178(8) Å, c = 7.1857(8) Å, V = 692.6(1) ų, Z = 2, R1 = 0.025, wR2 = 0.052 (all data). The structure contains four metal atom sites, two thereof occupied solely by Ti atoms, and two by different Ti/Mo mixtures. The former two correspond to the Zr sites, and the latter two to the V sites of the isostructural antimonide Zr₂V₆Sb₉. The crystal structure is comprised of chains of face‐sharing TiSb₈ square antiprisms, Ti/Mo tetrahedra and Sb atom pairs and squares. The electronic structure, computed with the LMTO approximation, is indicative of metallic properties. In addition to the dominating metal–Sb bonds, strong metal–metal and Sb–Sb bonds exist as well in Ti_5.42Mo_2.58Sb₉. The Mo content per metal site increases with increasing metal–metal interactions.     

Structure determination and relative properties of novel cubic borates MM'4(BO3)3 (M = Li, M' = Sr; M = Na, M' = Sr, Ba)

A series of novel borates, MM'4(BO3)3 (M = Li, M' = Sr; M = Na, M' = Sr, Ba), have been successfully synthesized by standard solid-state reaction. The crystal structures have been determined from powder X-ray diffraction data. They crystallize in the cubic space group Iad with large lattice parameters: a = 14.95066(5) A for LiSr4(BO3)3, a = 15.14629(6) A for NaSr4(BO3)3, and a = 15.80719(8) A for NaBa4(BO3)3. The structure was built up from 64 small cubic grids, in which the M' atoms took up the corner angle and the BO3 triangles or MO6 cubic octahedra filled in the interspaces. The isolated [BO3]3- anionic groups are perpendicular to each other, distributed along three 100 directions. The anisotropic polarizations were counteracting, forming an isotropic crystal. Sr and Ba atoms were found to be completely soluble in the solid solution NaSr(4-)xBax(BO3)3 (0 < or = x < or = 4). The photoluminescence of samples doped with the ions Eu2+ and Eu3+ was studied, and effective yellow and red emission was detected, respectively. The results are consistent with the crystallographic study. The DTA and TGA curves of them show that they are chemically stable and congruent melting compounds.     

K(6)Tl(2)Sb(3), a zintl phase with a novel heteroatomic (1)(infinity)[Tl4Sb(6)(12-)] chain

The title compound with heteratomic anionic chains [Tl(4)Sb(6)(12)(-)] has been discovered in the K-Tl-Sb system. The phase is obtained from a range of compositions near K(3)TlSb(1.5) following reaction first at 750-850 degrees C and then at 550 degrees C for one week or more. It crystallizes in the monoclinic system in space group C2/c, Z = 8, a = 9.951(1) A, b = 17.137(3) A, c = 19.640(6) A, and beta = 104.26(3) degrees. Swing-like (Tl(4)Sb(6))(12)(-) units consisting of alternating Sb and Tl atoms in four- and eight-membered rings are linked through Tl-Tl bonds to form infinite one-dimensional chains along a. EHTB calculations and resistivity measurements show that the compound is a semiconductor.     

Ternary rare-earth titanium antimonides RE2Ti(11-x)Sb(14+x) (RE = Sm, Gd, Tb, Yb)

The isostructural rare-earth titanium antimonides RE 2Ti 11 - x Sb 14 + x ( RE = Sm, Gd, Tb, Yb) have been synthesized by arc-melting reactions of the elements. Single-crystal X-ray diffraction revealed that they adopt a new structure type (Pearson symbol oP54, space group Pnma, Z = 2; a = 15.8865(6)-15.9529(9) A, b = 5.7164(2)-5.7135(3) A, c = 12.9244(5)-12.9442(7) A for RE = Sm-Yb). The structure consists of titanium-centered octahedra (CN6) and pentagonal bipyramids (CN7) connected to form a 3D framework whose cavities are filled with RE atoms. 1D linear skewers of titanium atoms, within face-sharing octahedral chains, and similar skewers of antimony atoms, associated with the titanium-centered pentagonal bipyramids, extend along the b direction. On proceeding from Sm 2Ti 11Sb 14 to Tb 2Ti 10.41(1)Sb 14.59(1) and Yb 2Ti 10.58(1)Sb 14.42(1), antimony atoms are disordered within some of the titanium sites. Resistivity measurements on the samarium and ytterbium members indicated metallic behavior.     

Self-assembly of D-penicillaminato M6M'8 (M = Ni(II), Pd(II), Pt(II); M' = Cu(I), Ag(I)) clusters and their organization into extended La(III)M6M'8 supramolecular structures

A series of chiral M(6)M'(8) cluster compounds having twelve free carboxylate groups, [M(6)M'(8)(D-pen-N,S)(12)X](5-) (M/M'/X = Pd(II)/Ag(I)/Cl(-) ([1](5-)), Pd(II)/Ag(I)/Br(-) ([2](5-)), Pd(II)/Ag(I)/I(-) ([3](5-)), Ni(II)/Ag(I)/Cl(-) ([4](5-)), Pt(II)/Ag(I)/Cl(-) ([5](5-)), Pd(II)/Cu(I)/Cl(-) ([6](5-)); D-H(2)pen = D-penicillamine), in which six cis-[M(D-pen-N,S)(2)](2-) square-planar units are bound to a [M'(8)X](7+) cubic core through sulfur-bridges, was synthesized by the reactions of cis-[M(D-pen-N,S)(2)](2-) with M' in water in the presence of halide ions. These M(6)M'(8) clusters readily reacted with La(3+) in aqueous buffer to form La(III)(2)M(6)M'(8) heterotrimetallic compounds, La(2)[1](CH(3)COO), La(2)[2](CH(3)COO), La(2)[3](CH(3)COO), La(2)[4](CH(3)COO), La(2)[5](CH(3)COO) and La(2)[6]Cl, in which the M(6)M'(8) cluster units are linked by La(3+) ions through carboxylate groups in a 1?:?2 ratio. While the La(III)(2)M(6)Ag(I)(8) compounds derived from [1](5-), [2](5-), [3](5-), [4](5-) and [5](5-) have a 1D helix supramolecular structure with a right-handedness, the La(III)(2)Pd(II)(6)Cu(I)(8) compound derived from [6](5-) has a 2D sheet-like structure with a triangular grid of the Pd(II)(6)Cu(I)(8) cluster units. When aqueous HCl was added to the reaction solution of [6](5-) and La(3+), another La(III)(2)Pd(II)(6)Cu(I)(8) heterotrimetallic compound, La(2)[6]Cl·HCl, in which the Pd(II)(6)Cu(I)(8) cluster units are linked by La(3+) ions to form a 2D structure with a rectangular grid, was produced. The solid-state structures of these La(III)(2)M(6)M'(8) compounds, determined by single-crystal X-ray crystallography, along with the spectroscopic properties of the M(6)M'(8) cluster compounds in solution, are described.     

Zr7(Sb,Se)4 – eine polare Variante des Nb7P4-Strukturtyps

Zr₇(Sb,Se)₄ – a Polar Variant of the Nb₇P₄ Structure Type Single crystals of Zr₇Sb_1.6(1)Se_2,4 were obtained by arc-melting of compressed mixtures of Zr, ZrSb₂, and ZrSe₂, followed by annealing at 1300 °C in an induction furnace using traces of iodine to promote crystal growth. The crystal structure (a = 375.98(4), b = 1662.6(2), c = 1476.7(2) pm, V = 923.1(2) 10⁶ pm³, Cmc2₁, Z = 4) was determined by single crystal X-ray means. Zr₇Sb_1.6(1)Se_2.4 forms a unique polar structure composed of condensed tri-capped trigonal prismatic Zr₉ clusters, being stabilized by interstitial Sb/Se atoms. The remaining Sb and Se atoms reside in mono- and bi-capped trigonal prismatic Zr₇ and Zr₈ clusters, respectively, of the extended cluster network. Characteristic structural distinctions and relations between Zr₇(Sb,Se)₄ and congeneric Zr₇P₄ are highlighted.     

Bonding analysis of metal-metal multiple bonds in R3M-M'R3 (M, M' = Cr, Mo, W; R = Cl, NMe2)

The bonding situation of homonuclear and heteronuclear metal-metal multiple bonds in R(3)M-M'R(3) (M, M' = Cr, Mo, W; R = Cl, NMe(2)) is investigated by density functional theory (DFT) calculations, with the help of energy decomposition analysis (EDA). The M-M' bond strength increases as M and M' become heavier. The strongest bond is predicted for the 5d-5d tungsten complexes (NMe(2))(3)W-W(NMe(2))(3) (D(e) = 103.6 kcal/mol) and Cl(3)W-WCl(3) (D(e) = 99.8 kcal/mol). Although the heteronuclear molecules with polar M-M' bonds are not known experimentally, the predicted bond dissociation energies of up to 94.1 kcal/mol for (NMe(2))(3)Mo-W(NMe(2))(3) indicate that they are stable enough to be isolated in the condensed phase. The results of the EDA show that the stronger R(3)M-M'R(3) bonds for heavier metal atoms can be ascribed to the larger electrostatic interaction caused by effective attraction between the expanding valence orbitals in one metal atom and the more positively charged nucleus in the other metal atom. The orbital interaction reveal that the covalency of the homonuclear and heteronuclear R(3)M-M'R(3) bonds is due to genuine triple bonds with one σ- and one degenerate π-symmetric component. The metal-metal bonds may be classified as triple bonds where π-bonding is much stronger than σ-bonding; however, the largest attraction comes from the quasiclassical contribution to the metal-metal bonding. The heterodimetallic species show only moderate polarity and their properties and stabilities are intermediate between the corresponding homodimetallic species, a fact which should allow for the experimental isolation of heterodinuclear species. CASPT2 calculations of Cl(3)M-MCl(3) (M = Cr, Mo, W) support the assignment of the molecules as triply bonded systems.     

A complete family of isostructural cluster compounds with cubane-like M(3)S(4)M' cores (M = Mo,W; M' = Ni,Pd, Pt): comparative crystallography and electrochemistry

By reaction of the geometrically incomplete cubane-like clusters [(eta(5)-Cp')(3)Mo(3)S(4))][pts] and [(eta(5)-Cp')(3)W(3)S(4)][pts] (Cp' = methylcyclopentadienyl; pts = p-toluenesulfonate) with group 10 alkene complexes, three new heterobimetallic clusters with cubane-like cluster cores were isolated: [(eta(5)-Cp')(3)W(3)S(4)M'(PPh(3))][pts] ([5][pts], M' = Pd; [6][pts], M' = Pt); [(eta(5)-Cp')(3)Mo(3)S(4)Ni(AsPh(3))][pts] ([7][pts]). The compounds [5][pts]-[7][pts] are completing the extensive series of clusters [(eta(5)-Cp')(3)M(3)S(4)M'(EPh(3))][pts] (M = Mo, W; M' = Ni, Pd, Pt; E = P, As) which allows the consequences of replacing a single type of atom on structural and NMR and UV/vis spectroscopic as well as electrochemical properties to be determined. Single-crystal X-ray structure determinations of [5][pts]-[7][pts] revealed that [5][pts] was not isomorphous to the other members of the series [(eta(5)-Cp')(3)M(3)S(4)M'(EPh(3))][pts] due to distinctly different cell parameters, which in the molecular structure of [5](+) is reflected in a slightly different orientation of the PPh(3) ligand. Electrochemical measurements on the series showed that the Mo-based clusters were more difficult to oxidize than their W-based analogues. The Pd-containing clusters underwent two-electron oxidation processes, whereas the Ni- and Pt-containing clusters underwent two separated one-electron oxidation processes.     

A New Family of Nonstoichiometric Layered Rare-Earth Tin Antimonides, RESn(x)()Sb(2) (RE = La, Ce, Pr, Nd, Sm): Crystal Structure of LaSn(0.75)Sb(2)

A new class of nonstoichiometric layered ternary rare-earth tin antimonides, RESn(x)()Sb(2) (RE = La, Ce, Pr, Nd, Sm), has been synthesized through reaction of the elements at 950 degrees C. In the lanthanum series LaSn(x)()Sb(2), tin can be incorporated from a maximum content of x approximately 0.7 or 0.8 to as low as x approximately 0.10. The structure of lanthanum tin diantimonide with the maximum tin content, LaSn(0.75)Sb(2), has been determined by single-crystal X-ray diffraction methods. It crystallizes in the orthorhombic space group -Cmcm with a = 4.2425(5) ?, b = 23.121(2) ?, c = 4.5053(6) ?, and Z = 4. The isostructural rare-earth analogues were characterized by powder X-ray diffraction. The structure of LaSn(0.75)Sb(2) comprises layers of composition "LaSb(2)" in which La atoms are coordinated by Sb atoms in a square-antiprismatic geometry. Between these layers reside chains of Sn atoms distributed over three crystallographically independent sites, each partially occupied at about 20%. The structure of LaSn(0.75)Sb(2) can be regarded as resulting from the excision of RE-Sb and Sb-Sb bonds in the related structures of binary rare-earth diantimonides, RESb(2), and then intercalation of Sn atoms between layers.     

Rare-earth metal-rich antimonides: syntheses, structures, and properties of Tm(3)Sb and Lu(7)Sb(3)

The two most metal-rich lanthanide antimony phases known were obtained from high-temperature solid state syntheses, that for Tm3Sb being of greater difficulty because of its apparent incongruent melting. The Tm3Sb phase crystallizes in the tetragonal space group P42/n (No. 86) with a Ti3P-type (Pearson: tP32) structure, a = 12.2294(5) Angstrom, c = 5.9852(5) Angstrom, and Z = 8. The phase Lu7Sb3 exhibits a Sc7As3-type tetragonal structure, I4/mcm (No. 140) (tI56), with a = 15.5974(7) Angstrom, c = 8.8130(7) Angstrom, and Z = 8. Both structures are described in terms of compact arrays of condensed chains of metal polyhedra (tetrahedral, tetrahedral star, trigonal prismatic, cubic) together with six- to nine-coordinate Sb in metal polyhedra. Magnetic susceptibility data on the paramagnetic Tm3Sb are also reported.     

Structures and bonding of the sandwich complexes [Ti(eta5-E5)2]2- (E = CH,N, P,As, Sb): a theoretical study

Quantum chemical calculations using gradient-corrected DFT at the BP86/TZ2P level of the compounds [Ti(eta(5)-E(5))(2)](2)(-) (E = CH, N, P, As, Sb) are reported. The nature of the metal-ligand bonding has been analyzed with an energy decomposition method, and the results are compared with [Fe(eta(5)-E(5))(2)]. The bonding in both series of complexes is more covalent than electrostatic. The energy decomposition analysis shows that the dominant orbital interactions in the negatively charged titanium species come from the (e(2)') Ti --> [(eta(5)-E(5))(2)](2)(-) back-donation (delta bonding) while the covalent bonding in the iron complexes come mainly from (e(1)' ') (Cp(-))(2) --> Fe(2+) donation (pi bonding). The nature of the metal-ligand interactions does not change very much for different ligands cyc-E(5) within the two series of compounds. The calculated bond dissociation energies for breaking one metal-ligand bond of the molecules [Ti(eta(5)-E(5))(2)](2)(-) shows for E the order P > As > Sb > N > CH. The central message of this work is that the complexes [Ti(eta(5)-E(5))(2)](2)(-) are delta bonded molecules.     

Structure determination and relative properties of novel noncentrosymmetric borates MM'4(BO3)3 (M = Na, M' = Ca and M = K, M' = Ca, Sr)

A series of novel noncentrosymmetric borates, MM'4(BO3)3 (M = Na, M' = Ca; M = K, M' = Ca, Sr), have been successfully synthesized via a standard solid-state reaction. The crystal structures have been determined by the SDPD (structure determination from powder diffraction) method. They crystallize in the noncentrosymmetric space group Ama2 with the following lattice parameters: a = 10.68004(11) A, b = 11.28574(11) A, c = 6.48521(6) A for NaCa4(BO3)3; a = 10.63455(10) A, b = 11.51705(11) A, c = 6.51942(6) A for KCa4(BO3)3; and a = 11.03843(8) A, b = 11.98974(9) A, c = 6.88446(5) A for KSr4(BO3)3. The fundamental building units are isolated BO3 anionic groups. Their second harmonic generation (SHG) coefficients were one-half (NaCa4(BO3)3), one-third (KCa4(BO3)3), and two-thirds (KSr4(BO3)3) as large as that of KH2PO4 (KDP). The infrared and UV-vis spectra of the three compounds are discussed. Moreover, a comparison of the structures of these novel compounds and three other novel cubic compounds with the same formula, MM'4(BO3)3 (M = Li, M' = Sr; M = Na, M' = Sr, Ba), is presented here.     

Die Antimonid–Triantimonidometallate(III) Cs6K3Sb[AlSb3] und Cs6K3Sb[GaSb3]

The Antimonide Triantimonidometallates(III) Cs₆K₃Sb[AlSb₃] and Cs₆K₃Sb[GaSb₃] The novel compounds Cs₆K₃Sb[AlSb₃] and Cs₆K₃Sb[GaSb₃] are formed from stoichiometric mixtures of Cs, AlSb (GaSb) and KSb in sealed niobium ampoules at 950 K. The hexagonal structures are especially characterized by one-dimensional rod packings ¹∞[Cs₆K₃Sb] which are formed from columns of condensed (Cs₆K_6/2) icosahedra. The icosahedra are centered by Sb^3-? anions. The trigonal planar anions [AlSb₃]^6-? and [GaSb₃]^6-? are embedded between the icosahedra columns, and they are coordinated by alkali metal atoms. The FIR spectra were assigned to the vibrations of the [MSb₃]^6-? anions, with respect to the 6 m2-D_3h symmetry. (P6₃/mmc, No. 194; a = 1101.7 and 1097.2 pm; c = 1158.9 and 1150.1 pm; Z = 2; Single crystal data: 574 and 546 reflections; R = 0.073 and 0.029. Distances:d(Al? Sb) = 265.4 pm; d(Ga? Sb) = 265.1 pm; d(Sb? Cs) = 401.6–423.0 pm; d(Sb? K) = 358.6–367.3 pm).     

Lanthanoid Antimonides Ln2Sb5 (Ln = Sm,Gd, Tb,Dy) and Rationalization of Chemical Bonding within the Antimony Polyanion by Combining the Zintl‐Klemm Concept with Bond‐Length Bond‐Strength Relationships

The title compounds are formed by peritectic reactions. Single crystals could be isolated from samples with high antimony content. Their structure was determined for Dy₂Sb₅ from four‐circle X‐ray diffractometer data: P2₁/m, a = 1306.6(1) pm, b = 416.27(4) pm, c = 1458.4(1) pm, β = 102.213(8)°, Z = 4, R = 0.061 for 2980 structure factors and 86 variable parameters. All dysprosium atoms have nine antimony neighbors forming tricapped trigonal prisms with Dy–Sb distances varying between 308 and 338 pm. The antimony atoms occupy ten different sites with greatly varying coordination. One extreme case is an antimony atom surrounded only by dysprosium atoms in trigonal prismatic arrangement, the other one is an antimony atom in distorted octahedral antimony coordination. The various antimony‐antimony interactions (with Sb–Sb distances varying between 284 and 338 pm) are rationalized by combining the Zintl‐Klemm concept with bond‐length bond‐strength considerations.     

Molecular structures of two metal tetrakis(tetrahydroborates), Zr(BH4)(4) and U(BH4)(4): equilibrium conformations and barriers to internal rotation of the triply bridging BH4 groups

The molecular structures of Zr[(mu-H)(3)BH](4) and U[(mu-H)(3)BH](4) have been investigated by density functional theory (DFT) calculations and gas electron diffraction (GED). The triply bridged bonding mode of the tetrahydroborate groups in the former is confirmed, but both DFT calculations and GED structure refinements indicate that the BH(4) groups are rotated some 12 degrees away from the orientation in which the three bridging B-H bonds are staggered with respect to the opposing ZrB(3) fragment. As a result the symmetry of the equilibrium conformation is reduced from T(d) to T. Bond distances and valence angles are as follows (DFT/GED): Zr-B = 232.2/232.4(5) pm; Zr-H(b) = 214.8/214.4(6) pm; B-H(b) = 125.3/127.8(8) pm; B-H(t) = 119.4/118.8(17) pm; angle ZrBH(b) = 66.2/65.6(3) degrees; the smallest dihedral angle of type tau(BZrBH(b)) = 48/45(2) degrees. DFT calculations on Hf(BH(4))(4) indicate that the structure of this molecule is very similar to that of the Zr analogue. Matrix-isolation IR spectroscopy and DFT calculations on U(BH(4))(4) show that while the polymeric solid-state structure is characterized by terminal triply bridging and metal-metal bridging bidentate BH(4) groups, all BH(4) groups are triply bridging in the gaseous monomer. Calculations with one of the two nonbonding 5f electrons on U occupying an a(1) and the other distributed equally among the three t(2) orbitals indicate that the equilibrium conformation has T(d) symmetry, i.e. that the three B-H(b) bonds of each tetrahydroborate group are exactly staggered with respect to the opposing UB(3) fragment with tau(BUBH(b)) = 60 degrees. Calculations including spin-orbit interactions indicate that Jahn-Teller distortions from T(d) symmetry are either absent or very small. The best agreement between observed and calculated GED intensity data was obtained for a model of T(d) symmetry, but models of T symmetry with dihedral angles tau(BUBH(b)) > 42 degrees cannot be ruled out. Bond distances and valence angles are as follows (DFT/GED): U-B = 248.8/251.2(4) pm; U-H(b) = 227.7/231.5(6) pm; B-H(b) = 126.0/131.6(5) pm, B-H(t) = 119.5/117.8(11) pm; angle UBH(b) = 65.6/63.1(3) degrees. It is suggested that the different equilibrium conformations of the three molecules are determined primarily by repulsion between bridging H atoms in different tetrahydroborate groups.