Crystallite orientation in stretched polychloroprene networks. II

The orientation of crystallites grown isothermally in several drawn trans-polychloroprene networks is studied as a function of crystallization temperature t_x, degree of crystallinity ω, and elongation ratio α. The orientation distribution is particularly simple for this polymer since the crystallographic c axis (chain axis) orients preferentially along the stretching direction, while a and b are randomly arranged about c. Hence the parameter cos² χ_c adequately characterizes the distribution, where χ_c is the angle between the c axis and the fiber axis, and the average is taken over all crystallites. A treatment due to Krigbaum and Roe is utilized to obtain values of v (the number of statistical segments comprising the crystallization nucleus of critical size) through comparison of the average orientation of crystallites and amorphous statistical segments. The behavior observed falls into two categories. First, if the initial amorphous network is well oriented, 〈cos² χ_c〉 is independent of crystallinity during both crystallization and melting, and v varies with t_z (or the degree of supercooling) as predicted by nucleation theory. If different networks are to have the same crystallite orientation distribution, they must not only be crystallized at the same supercooling, but must also have the same distribution of amorphous segment orientations. Both the relative elongation and the network crosslink density affect the latter distribution. Next, we consider the second category. If the initial amorphous orientation is poor, 〈cos² χ_c〉 decreases linearly during crystallization and increases along approximately the same path during melting. Further, 〈cos² χ_c〉 for a given t_z yields v values which are too large. These two behaviors can be explained if, in the former case, nucleation involves the best oriented statistical segments of all network chains, while in the latter there is a selection according to the chain displacement vector orientation. Thus, if the amorphous orientation is poor, both the orientation and thermodynamic stability of the crystallites decreases with further crystallization. If this decreased stability is reflected in shorter fold lengths, the reversible variation of long period spacing with temperature reported earlier for an oriented polychloroprene network can also be explained as a preferential melting process.     

The Crystal Structure of Enniatin B

The X-ray crystal structure of enniatin B (trigonal (hexagonal axes), a = 14.626 Å, c = 16.309 Å, space group R3) is described and the conformation compared to results of other investigations.     

Mg2[BN2]Cl and Mg8[BN2]5I: Novel Magnesium Nitridoborate Halides — Syntheses,Crystal Structures,and Vibrational Spectra

The title compounds have been synthesized at 1473 K from stoichiometric mixtures of the binary components Mg₃N₂, MgX₂ (X = Cl, I) and BN in arc‐welded steel ampoules encapsulated in evacuated silica tubes. Mg₂[BN₂]Cl ( 1 ) and Mg₈[BN₂]₅I ( 2 ) crystallize in the orthorhombic space groups Pbca (no. 61) and Imma (no. 74), respectively, with a = 6.6139(8)Å, b = 9.766(1)Å, c = 10.600(1)Å, Z = 8 for 1 and a = 13.535(3)Å, b = 9.350(2)Å, c = 11.194(2)Å, Z = 4 for 2 . The crystal structures are characterized mainly by Mg₆ trigonal prisms which are condensed to 3D frameworks in different ways. Part of the trigonal prisms are centered by the [N—B—N]^3— anions and other voids in the framework by the X^— anions. The magnesium environment around Cl^— is a very distorted monocapped trigonal prism (CN = 6+1) and that of I^— is a bicapped heptagonal prism (CN = 14+2). The bond lengths and bond angles for the relevant [BN₂]^3— anions are d(B—N) = 1.330 — 1.338Å, ∠N—B—N = 175.8° in 1 and d(B—N) = 1.330 — 1.339Å, ∠N—B—N = 176.8° — 178.0° in 2 . The vibrational spectra of the title compounds have been recorded and interpreted based on the D_∞h symmetry of the relevant [N—B—N]^3— groups considering the site symmetry splitting.     

Crystal structure and magnetic properties of a Cs3Nb2I9 bioctahedral complex

A cluster complex Cs₃Nb₂I₉ is obtained by a high-temperature reaction of niobium, iodine, and cesium iodide. Its crystal structure is determined: trigonal space group P6₃/mmc, a = 8.2463(3) Å, c = 19.5419(14) Å, V = 1150.84(10) ų, R(F) = 0.0614. The compound obtained is characterized by temperature independent paramagnetism in the temperature range 70–290 K.     

Three-dimensional crystalline order in an atactic comblike polymer

The production of oriented “crystalline” fibers of an atactic polymer, poly{1-[6-(4-biphenylyloxy)hexyloxycarbonyl]ethylene} is reported. The x-ray diffraction is consistent with a two-chain unit cell with a = b = 23.5 Å, c = 6.48 Å, and γ = 120. Although the cell is essentially hexagonal, the absence of screw symmetry along the polymer chain reduces the crystal symmetry to P A packing model consistent with these data is proposed.     

Syntheses and Crystal Structures of the Novel Ternary Thioborates Na3BS3, K3BS3, and Rb3BS3

The orthothioborates Na₃BS₃, K₃BS₃ and Rb₃BS₃ were prepared from the metal sulfides, amorphous boron and sulfur in solid state reactions at temperatures between 923 and 973 K. In a systematic study on the structural cation influence on this type of ternary compounds, the crystal structures were determined by single crystal X‐ray diffraction experiments. Na₃BS₃ crystallizes in the monoclinic space group C2/c (No. 15) with a = 11.853(14) Å, b = 6.664(10) Å, c = 8.406(10) Å, β = 118.18(2)° and Z = 4. K₃BS₃ and Rb₃BS₃ are monoclinic, space group P2₁/c (No. 14) with a = 10.061(3) Å, b = 6.210(2) Å, c = 12.538(3) Å, β = 112.97(2) and a = 10.215(3) Å, b = 6.407(1) Å, c = 13.069(6) Å, β = 103.64(5)°, Z = 4. The potassium and rubidium compounds are not isotypic. All three compounds contain isolated [BS₃]^3– anions with boron in a trigonal‐planar coordination. The sodium cations in Na₃BS₃ are located between layers of orthothioborate anions, in the case of K₃BS₃ and Rb₃BS₃ stacks of [BS₃]^3– entities are connected via the corresponding cations. X‐ray powder patterns were measured and compared to calculated ones obtained from single crystal X‐ray structure determinations.     

Molecular orientation in poly(vinyl chloride) studied by Raman spectroscopy and birefringence measurements

The ratios of the intensities of Raman scattering in the C? CI stretching region for eight combinations of sample orientation and directions of polarization of incident and scattered light have been measured for 15 samples of poly(vinyl chloride) (PVC) containing 0, 5, 10, 15 or 20 pph dioctyl sebacate (DOS) plasticizer which had been drawn uniaxially at 22, 70, 75, 80, or 90°C to draw ratios in the range 1–4.5. The birefringences of the samples were also measured. The Raman data were analyzed to give 〈P₂(cosθ)〉_cryst and 〈P₄(cosθ)〉_cryst, the values of the second- and fourth-order Legendre polynomials in cosθ averaged over the distribution of orientations of the crystallites, where θ is the angle between the c axis of a typical crystallite and the draw direction. Comparison of 〈P₂(cosθ)〉_cryst with the birefrigence showed that the crystallites are more highly oriented than the noncrystalline material in samples containing the higher amounts of plasticizer drawn at the higher temperatures. A value of 13.0 × 10^?3 was deduced for the birefringence of fully oriented PVC. The values of 〈P₄(cosθ)〉_cryst for a given 〈P₂(cosθ)〉_cryst were found to be higher than predicted by calculations based on two simple models, the pseudoaffine rigid-rod rotation model and the affine rubber elasticity model.     

Synthesis and structure of a polymeric ten-coordinate rare earth metal complex with nta ligand: {[EuIII(C-nta)(T-nta)]·3H2O} n with a novel cage-like 3-D structure

The polymeric ten-coordinate rare earth metal (RE) complex with nta, {[Eu^III(C-nta)(T-nta)] · 3H₂O} _n , has been synthesized in aqueous solution and characterized by FT-IR, elemental analyses, TG-DTA and single-crystal X-ray diffraction technique. The {[Eu^III(C-nta)(T-nta)] · 3H₂O} _n crystallizes in the cubic system with P2₁3 space group, a = b = c = 12.4153(3) Å, V = 1913.69(8) ų, Z = 4, M = 582.24 g mol^?1, D _c = 2.021 Mg m^?3, μ = 3.360 mm^?1, F(000) = 1148, and its structure is refined to R ₁(F) = 0.0204 for 1277 observed reflections [I ≥ 2.0σ(I)]. The coordination polyhedron adopts distorted C_3v mono-top-capped & tri-lateral-capped trigonal prismatic conformation (MT&TL-TP); the three-dimensional geometry is a cage-like 3-D structure. According to thermal analyses, the collapsing temperature of the crystal structure is 173°C, indicating that its crystal structure is very stable.     

Electronic Structures of Highly Symmetrical Compounds of f Elements. 34 [1] Synthesis and Spectroscopic Characterization of Biscyclohexylisocyanide Adducts derived from the Tris(bis(trimethylsilyl)amido)lanthanide(III) Moiety as well as Crystal,Molecular, and Electronic Structure of the Corresponding Neodymium Compound

The reaction of tris(bis(trimethylsilyl)amido)lanthanide(III) (Ln(btmsa)₃) with two equiv. of cyclohexylisocyanide gives good yields of complexes of composition Ln(btmsa)₃(CNC₆H₁₁)₂ (Ln = Y( 1 ), La( 2 ), Ce( 3 ), Pr( 4 ), Nd( 5 ), Sm( 6 ), Eu( 7 ), Tb( 8 ), Dy( 9 ), Ho( 10 ), Tm( 11 ) and Yb( 12 )). Complex 5 crystallizes in the monoclinic space group C2/c with a = 25.689(8) Å, b = 12.165(2) Å, c = 17.895(15) Å, β = 122.47 (2)°, V = 4718.07 ų, Z = 4 and R = 0.0342. The structure of compound 5 shows the five‐coordinate Nd³⁺ ion in a nearly exact trigonal bipyramidal environment with two CNC₆H₁₁ molecules in the axial and the three btmsa ligands in the equatorial positions. The linear dichroism spectrum of a single crystal of complex 5 was measured at room temperature, and the absorption spectrum of powdered material at low temperatures. From the spectra obtained a truncated crystal field (CF) splitting pattern is derived, and simulated by fitting the parameters of a phenomenological Hamiltonian. For 80 assignments a reduced r.m.s. deviation of 20.7 cm^—1 is achieved. Making use of the calculated wavefunctions and eigenvalues the experimentally determined temperature dependence of μ²_eff could be reproduced by adopting an orbital reduction factor k = 0.991, and on the basis of the CF parameters used the experimentally oriented non‐relativistic molecular orbital scheme of compound 5 is set up.     

A Revised Structure Model for the UCl6 Structure Type,Novel Modifications of UCl6 and UBr5, and a Comment on the Modifications of Protactinium Pentabromides

The redetermination of the crystal structure of trigonal UCl₆, which is the eponym for the UCl₆ structure type, showed that certain atomic coordinates had been incorrectly reported. This led to noticeably different U−Cl distances within the octahedral UCl₆ molecule (2.41 and 2.51 Å). Within the revised structure model presented here, which is based on single crystal data as well as quantum chemical calculations, all U−Cl distances are essentially equal within standard uncertainty (2.431(5), 2.437(5), and 2.439(6) Å). This room temperature modification, called rt-UCl₆, crystallizes in the trigonal space group P m1, No. 164, hP21, with a=10.907(2), c=5.9883(12) Å, V=616.9(2) ų, Z=3 at T=253 K. A new low-temperature (lt) modification of UCl₆ is also presented that was obtained by cooling a single crystal of rt-UCl_6. The phase change occurs between 150 and 175 K. lt-UCl₆ crystallizes isotypic to a low-temperature modification of SF₆ in the monoclinic crystal system, space group C2/m, No. 12, mS42, with a=17.847(4), b=10.8347(18), c=6.2670(17) Å, β=96.68(2)°, V=1203.6(5) ų, Z=6 at 100 K. The Cl anions form a close-packed structure corresponding to the α-Sm type with uranium atoms in the octahedral voids. During the synthesis of UBr₅ a new modification was obtained that crystallizes in the triclinic crystal system, space group P , No. 2, aP36, with a=10.4021(6), b=11.1620(6), c=12.2942(7) Å, α=68.3340(10)°, β=69.6410(10)° and γ=89.5290(10)°, V=1231.84(12) ų, Z=3 at T=100 K. In this structure the UBr₅ units are dimerized to U₂Br₁₀ molecules. The Br anions also form a close-packed structure of the α-Sm type with adjacent uranium atoms in the octahedral voids. Comparisons of the crystal structures of the compounds MX₅ (M=Pa, U; X=Cl, Br) show that the crystal structure of monoclinic α-PaBr₅ is probably not correct.     

Syntheses,and Crystal Structures of Indium Complexes with η2‐Piperidinyldithiocarbamate and η2‐Pyridine‐2‐Thionate Containing Ligands: Structures of [In(η2‐S2CNC5H10)3] and [In(η2‐pyS)3]

The η²‐thio‐indium complexes [In(η²‐thio)₃] (thio = S₂CNC₅H₁₀, 2 ; SNC₄H₄, (pyridine‐2‐thionate, pyS, 3 ) and [In(η²‐pyS)₂(η²‐acac)], 4 , (acac: acetylacetonate) are prepared by reacting the tris(η²‐acac)indium complex [In(η²‐acac)₃], 1 with HS₂CNC₅H₁₀, pySH, and pySH with ratios of 1:3, 1:3, and 1:2 in dichloromethane at room temperature, respectively. All of these complexes are identified by spectroscopic methods and complexes 2 and 3 are determined by single‐crystal X‐ray diffraction. Crystal data for 2 : space group, C2/c with a = 13.5489(8) Å, b = 12.1821(7) Å, c = 16.0893(10) Å, β = 101.654(1)°, V = 2600.9(3) ų, and Z = 4. The structure was refined to R = 0.033 and Rw = 0.086; Crystal data for 3 : space group, P2₁ with a = 8.8064 (6) Å, b = 11.7047 (8) Å, c = 9.4046 (7) Å, β = 114.78 (1)°, V = 880.13(11) ų, and Z = 2. The structure was refined to R = 0.030 and Rw = 0.061. The geometry around the metal atom of the two complexes is a trigonal prismatic coordination. The piperidinyldithiocarbamate and pyridine‐2‐thionate ligands, respectively, coordinate to the indium metal center through the two sulfur atoms and one sulfur and one nitrogen atoms, respectively. The short C‐N bond length in the range of 1.322(4)–1.381(6) Å in 2 and C‐S bond length in the range of 1.715(2)–1.753(6) Å in 2 and 3 , respectively, indicate considerable partial double bond character.     

Stress-optical coefficient of cis-1,4-polybutadiene and cis-1,4-polyisoprene networks. Measurements on cis-1,4-polybutadiene networks and theoretical interpretation

Stress, strain, and birefringence measurements have been carried out on swollen and unswollen networks of ′cis-1,4-polybutadiene polymers. Neither stress-strain nor birefringence-strain relations of unswollen specimens obey the Gaussian network theory, but both can be fitted by the Mooney-Rivlin equation. On the contrary, data on specimens swollen in tetralin, decalin, benzene, and carbon tetrachloride strictly obey the Gaussian network theory. Existing methods for evaluating the temperature coefficient of the unperturbed dimensions, d In 〈r²〉/dT, from the stress-temperature relation are applied to the present data and discussed in some detail. It is concluded that reliable values of d In 〈r²〉/dT are not obtainable from data on unswollen samples because of the pronounced non-Gaussian effect. The value 7.5 ų for the optical anisotropy ų (an alternative to the stress-optical coefficient) for unswollen specimens is markedly larger than values (5.8 ų on the average) for swollen specimens. This is interpreted as due to the shortrange orientational order among polymer segments. The quantities 〈r²〉, ΔΓ, and their temperature coefficients are calculated for both cis-1,4-polybutadiene and cis-1,4-polyisoprene chains, on the basis of the rotational isomeric state approximation for bond rotations. Values of ΔΓ for cis-1,4-polybutadiene calculated using Clément and Bothorel's set of anisotropic bond polarizabilities are in good agreement with observed values for swollen specimens. Those for cis-1,4-polyisoprene obtained using the same set of anisotropic bond polarizabilities are somewhat smaller than observed values for unswollen specimens. This departure is in the direction expected from the behavior of ΔΓ upon swelling (i.e., a decrease in ΔΓ upon swelling).     

Structure and Bonding of the Mixed‐Valent Platinum Trihalides,PtCl3 and PtBr3

The isotypical crystal structures of the mixed valent trihalides PtCl₃ and PtBr₃ were redetermined by single crystal methods (space group R3¯; trigonal setting; PtCl₃: a = 21.213Å, c = 8.600Å, c/a = 0.4054; Z = 36; 1719 hkl; R = 0.035; PtBr₃: a = 22.318Å, c = 9.034Å; c/a = 0.4048; Z = 36; 1606 hkl; R = 0.027). A cubic closest packing of X^— anions forms the basis of an optimized arrangement of cuboctahedrally [Pt₆X₁₂] cluster molecules with Pt^II and enantiomers of helical chains of edge‐condensed [PtX₂X_4/2] octahedra with Pt^IV in cis‐Δ‐ and cis‐Λ‐configuration, respectively. The bond lengths vary with the function of the X^— ligands (d¯(Pt^II—X) = 2.315 and 2.445Å; d¯(Pt^II—Pt^II) = 3.336 and 3.492Å; d(Pt^IV—X) = 2.286 — 2.417Å and 2.437 — 2.563Å). The Pt^II atoms are shifted outwards the X₁₂ cuboctahedra by 0.045Å and 0.024Å, respectively. The symmetry governed Periodic Nodal Surface, PNS, perfectly separates the regions of different valencies. Quantum chemical calculations exclude the possible additional interactions between Pt^II and one of the exo‐ligands of Pt^IV.     

The Cluster Compounds Ag[W6Br14] and Ag2[W6Br14]

The reaction of W₆Br₁₂ with AgBr in evacuated silica tubes (temperature gradient 925 K/915 K) yielded brownish black octahedra of Ag[W₆Br₁₄] ( I ) and yellowish green platelets of Ag₂[W₆Br₁₄] ( II ) both in the low temperature zone. ( I ) crystallizes cubically (Pn3 (no. 201); a = 13.355 Å, Z = 4) and ( II ) monoclinically (P2₁/c (no. 14); a = 9.384 Å, b = 15.383 Å, c = 9.522 Å, β = 117.34°, Z = 2). Both crystal structures contain isolated cluster anions, namely [(W₆Brⁱ₈)Br^a₆]^1– and [(W₆Brⁱ₈)Br^a₆])]^2–, respectively, with the mean distances and angles: ( I ) d(W–W) = 2.648 Å, d(W–Brⁱ) = 2.617 Å, d(W–Br^a) = 2.575 Å, d(Brⁱ…Brⁱ) = 3.700 Å, d(Brⁱ…Br^a) = 3.692 Å, ∠W–Brⁱ–W = 60.78°. ( II ) d(W–W) = 2.633 Å, d(W–Brⁱ) = 2.624 Å, d(W–Br^a) = 2.613 Å, d(Brⁱ…Brⁱ) = 3.710 Å, d(Brⁱ…Br^a) = 3.707 Å, ∠W–Brⁱ–W = 60.23°. The Ag⁺ cations are trigonal antiprismatically coordinated in ( I ) with d(Ag–Br) = 2.855 Å, but distorted trigonally planar in ( II ) with d(Ag–Br) = 2.588–2.672 Å. The structural details of hitherto known compounds with [W₆Br₁₄] anions will be discussed.     

Crystal and Molecular Structure of the bis-Ethyl Urethane of 5,7-Dodecadiyn-1,12,diol (ETCD)

Grown from ethyl acetate solution, the bis-ethylurethane of 5,7-dodecadiyn-1,12-diol is a monoclinic crystal, a = 16.9740(16), b = 4.9770(5), c = 11.0874(11) Å; β = 101.869(6)°; Z = 2; V = 916.63(16) ų. The crystal structure contains two N─H…O hydrogen bonds per molecule and has nearly ideal parameters (d = 4.977 Å, ? = 45.8°, R = 3.477 Å) for solid-state polymerization.     

Syntheses and Crystal Structures of the Cluster Compounds A2[(W6Br)Br] with A = K,Rb, Cs

K₂W₆Br₁₄ ( I ), Rb₂W₆Br₁₄ ( II ), and Cs₂W₆Br₁₄ ( III ) were formed by reactions of W₆Br₁₂ with the corresponding alkali metal bromides in evacuated silica tubes with a temperature gradient of 925 K/915 K. ( I ) crystallizes in the cubic space group Pn3 (no. 201), a = 13.808 Å, Z = 4, cP88. ( II ) crystallizes in the monoclinic space group C2/c (no. 15), a = 20.301 Å, b = 15.396 Å, c = 9.720 Å, β = 115.69°, Z = 4, mC88. ( III ) crystallizes in the trigonal space group P31c (no. 163), a = 10.180 Å, c = 15.125 Å, Z = 2, hP44. The crystal structures are composed of the isolated [(W₆Br)Br]^2– cluster anions and the alkali metal cations (d(W–W) = 2.635(2) Å, d(W–Brⁱ) = 2.624(4) Å, d(W–Br^a) = 2.595(4) Å). The shape of the anions is influenced by the crystal field symmetry, but the mean bond lengths are not changed by the cation size. The packing of the cluster anions corresponds to ccp pattern in ( I ) and hcp pattern in ( II ) and ( III ), respectively. The alkali metal cations in the octahedral holes are coordinated only by the Br^a ligands while those in the tetrahedral and trigonal-bipyramidal cavities are surrounded by Br^a and Brⁱ ligands. The details will be discussed and compared with other structures.     

Synthesis,Crystal Structure and Magnetic Properties of Na3OsO5

Na₃OsO₅ has been synthesized by solid state reaction of Na₂O₂ and osmium powder under a flow of oxygen. Na₃OsO₅ crystallizes trigonal in space group P3₁21 with a = 5.5529(2) Å, c = 13.4726(8) Å, V = 359.77(3) ų, Z = 3, 958 independent reflections, R₁ = 1,97 %, wR₂ = 4.27 %. The crystal structure consists of OsO₅ trigonal bipyramids separated by sodium cations, and is isostructural to Na₃ReO₅. The osmium atoms adopt a packing analogous to ccp, where Na occupies the octahedral and tetrahedral vacancies, so the cation structure is derived from the Li₃Bi structure type. Features of the synthesis of Na₃OsO₅ and related osmates are discussed. Na₃OsO₅ shows paramagnetic behaviour down to 25 K where it orders antiferromagnetically. Below 7 K a weak ferromagnetic contribution is detected. The paramagnetic region of the 5d¹ system has been successfully described in the temperature range 50 – 330 K accounting for strong spin‐orbit coupling, ligand‐field potential of D_3h symmetry (corresponding to the trigonal bipyramidal unit), and cooperative magnetic effects (molecular field parameter λ_MF).     

Hetero‐metallic Lanthanide CPs Involving Sodium: Synthesis,Crystal Structure,and Luminescence Properties

[TbNa(4‐msal)₄(phen)₂]_n ( 1 ) (4‐msal = 4‐methyl salicylic acid), a new hetero‐metallic lanthanide coordination polymer (CP) involving sodium was synthesized. It crystallizes in the monoclinic space group P2₁/n, with a = 20.4809(9) Å, b = 9.8183(2) Å, c = 26.1987(11) Å, α = 90.00°, β = 112.922(5)°, γ = 90.00°, V = 4852.2(3) ų, and Z = 4. The complex was characterized by single crystal and powder X‐ray diffraction, elemental analysis (EA), and Fourier transform infrared (FT‐IR) and luminescence spectroscopy. The luminescence properties of a powder sample of 1 were studied at room temperature and the luminescence lifetime and total quantum yield (QY) were determined.     

Four New Thioantimonates(III) with the General Formula [TM(tren)]Sb4S7 (TM = Mn,Fe, Co,Zn) with the Transition Metal as Part of a Thioantimonate(III) Network Synthesized under Solvothermal Conditions and Tuning of the Optical Band Gap by the Transition Metal Cation

Four new thioantimonate(III) compounds with the general formula [TM(tren)]Sb₄S₇, TM = Mn 1 , Fe 2 , Co 3 and Zn 4 , were synthesized under solvothermal conditions by reacting elemental TM, Sb and S in an aqueous solution of tren (tren = tris(2‐aminoethyl)amine). All compounds crystallize in the monoclinic space group P2₁/n with four formula units in the unit cell. Single crystal X‐ray analyses of 1 [a = 8.008(2), b = 10.626(2), c = 25.991(5) Å, β = 90.71(3)°, V = 2211.4(8) ų], 2 [a = 8.0030(2), b = 10.5619(2), c = 25.955(5) Å, β = 90.809(3)°, V = 2193.69(8) ų], 3 [a = 7.962(2), b = 10.541(2), c = 25.897(5) Å, β = 90.90(3)°, V = 2173.0(8) ų] and 4 [a = 7.978(2), b = 10.625(2), c = 25.901(5) Å, β = 90.75(3)°, V = 2195.2(8) ų] reveal that the compounds are isostructural. The [Sb₄S₇]^2‐ anions are composed of three SbS₃ trigonal pyramids and one SbS₄ unit as primary building units (PBU). The PBUs share common edges and corners to form semicubes (Sb₃S₄) which may be regarded as secondary building units (SBU). The SBUs and SbS₃ pyramids are joined in an alternating fashion yielding the equation/tex2gif-stack-1.gif[Sb₄S₇^‐] anionic chain which is directed along [100]. Weaker Sb‐S bonding interactions between neighbored chains lead to the formation of layers within the (001) plane which contain pockets that are occupied by the cations. The TM²⁺ ions are in a trigonal bipyramidal environment of four N atoms of the tren ligand and one S atom of the thioantimonate(III) anion. The optical band gaps depend on the TM²⁺ ion and amount to 3.11 eV for 1 , 2.04 eV for 2 , 2.45 eV for 3 , and 2.60 eV for 4 .     

Metal Vacancy Ordering in an Antiperovskite Resulting in Two Modifications of Fe2SeO

Small, red Fe₂SeO single crystals in two modifications were obtained from a CsCl flux. The metastable α‐phase is pseudo‐tetragonal (Cmce, a=16.4492(8) Å, b=11.1392(4) Å, c=11.1392(4) Å), whereas the β‐phase is trigonal (P3₁, a=9.8349(4) Å, c=6.9591(4) Å)) and thermodynamically stable within a narrow temperature range. Both crystal structures were solved from twinned specimens. The enantiomers of the β‐phase appear as racemic mixtures. Selenium and oxygen form two individual interpenetrating primitive cubic lattices, giving a bcc packing. A quasi‐octahedrally coordinated iron atom is found close to the center of each surface of the selenium sublattice. The difference between the α‐ and β‐phases is the distribution of iron at 2/3 of the surfaces. α‐ and β‐Fe₂SeO are comparable with metal‐vacancy‐ordered antiperovskites. Each Fe/O lattice can also be described in terms of vertex‐sharing OFe₄ tetrahedra, with a crystal structure similar to that of an antisilicate. Iron is divalent and has a high‐spin d⁶ (S=2) configuration. The β‐phase exhibits magnetoelectric coupling.