Synthese und Kristallstrukturen der Nitridodiolato-Osmate(VI) PPh4[OsNCl2(O2C2H4)] und PPh4[OsNCl2(O2C2Me4)] · 2 THF

Syntheses and Crystal Structures of the Nitridodiolato Osmates(VI) PPh₄[OsNCl₂(O₂C₂H₄)] and PPh₄[OsNCl₂(O₂C₂Me₄)] · 2 THF The title compounds were prepared by the reaction of PPh₄[OsNCl₄] with glycole and pinacole, respectively, in CH₂Cl₂ and THF, respectively, in the presence of triethylamine, forming orange-red single crystals. According to the crystal structure determinations the compounds have ionic structures. In the anions the nitrido ligand occupies the apical position of the distorted tetragonal pyramid, and the two chlorine atoms and the two oxygen atoms of the diolato ligands are in equatorial positions. PPh₄[OsNCl₂(O₂C₂H₄)] : Space group P2₁/n, Z = 4, 3 331 observed unique reflections, R = 0.031. Lattice dimensions at 19°C: a = 1 750.3, b = 816.8, c = 1 816.5 pm, β = 95.16°. PPh₄[OsNCl₂(O₂C₂Me₄)] · 2 THF : Space group P1 , Z = 2, 5 238 observed unique reflections, R = 0.051. Lattice dimensions at -80°C: a = 898.9, b = 1 405.1, c = 1 518.6 pm, α = 93.66°, β = 92.89°, γ = 92.51°.     

Halogeno-Nitrosylkomplexe von Molybdän und Wolfram. Die Kristallstrukturen von [Na2(15-Krone-5)2(CH3CN)][MoCl4(NO)2] und [Na(15-Krone-5)]2[MoF4Cl(NO)]

Halogeno-Nitrosyl Complexes of Molybdenum and Tungsten. Crystal Structures of [Na₂(15-Crown-5)₂(CH₃CN)][MoCl₄(NO)₂] and [Na(15-Crown-5)]₂[MoF₄Cl(NO)] MoCl₂(NO)₂ and WCl₂(NO)₂, respectively, react with excess sodium fluoride in acetonitrile at room temperature and in the presence of 15-crown-5 to give crystalline mixtures, which consist of the title compounds, respectively of [Na(15-crown-5)]₂[WCl₄(NO)₂] and [Na(15-crown-5)]₂[WF₄Cl(NO)], and which can be separated by selection. The complexes are characterized by their i.r. spectra, the molybdenum compounds additionally by crystal structure determinations. [Na₂(15-crown-5)₂(CH₃CN)][MoCl₄(NO)₂]: Space group P2₁, Z = 2, 5415 independent unique reflexions, R = 0.039. Lattice dimensions at ?10°C: a = 984.3, b = 1231.1, c = 1483.0 pm, β = 105.67°. The compound consists of cations [Ne(l5-crown-5)(CH₃CN)]⁺, in which the sodium ion is surrounded by the five O-atoms of the crown ether and by the N-atom of the acetonitrile molecule, as well as of anions, which form an ion pair {Na(15-crown-5)[MoCl₄(NO)₂]}^?. In the in pairs the sodium ion is coordinated by the five oxygen atoms of the crown ether and by two chlorine atoms of the [MoCI₄(NO)₂]^2? unit. The nitrosyl ligands take the cis-position a t the molybdenum atom which is in a distorted octahedrally fashion. [Na(15-crown-5)]₂[MoF₄Cl(NO)]. Space group C2/c, Z = 4, 1933 independent unique reflexions, R = 0.078. Lattice dimensions at ?7O°C: D : 1.585.8, b = 1171.5, c = 1771.5 pm, β = 114.91°. The compound forms an ion triple, in which the sodium ions are linked to five oxygen atoms each of the crown ether molecules, and to two F-atoms of the [MoF₄Cl(NO)]^2? unit. The F-atom which is arranged in trans-position to the nitrosyl ligand coordinates with both sodium ions; thus an unusual T-shaped arrangement results for this F-atom. The sole terminal F-Atom and the Cl-atom are disordered in two positions.     

[Na(12-Krone-4)2]2[Ni(Se4)2] · DMF; Synthese,Kristallstruktur und magnetisches Verhalten

[Na(12-Crown-4)₂]₂[Ni(Se₄)₂] · DMF; Synthesis, Crystal Structure, and Magnetic Behaviour The title compound has been prepared from NiCl₂ and sodium polyselenide in dimethylformamide solution in the presence of 12-crown-4, forming black crystal needles. They were characterized by an X-ray structure determination, by FIR spectroscopy as well as by the magnetic behaviour. [Na(12-crown-4)₂]₂[Ni(Se₄)₂] · DMF crystallizes monoclinically in the space group P2₁, 3650 observed unique reflections, R = 0.046. Lattice dimensions at ?80°C: a = 1020.3(2); b = 1889.5(2); c = 1498.7(3) pm; β = 108.29(1)°. The compound has an ionic structure, in which the sodium atoms of the [Na(12-crown-4)₂]⁺ cations are coordinated by the oxygen atoms of the crown ether molecules in an antiprismatic fashion. The nickel atom of the anion [Ni(Se₄)₂]^2? is surrounded by four selenium atoms of the tetraselenide chelates in an almost planar environment. The DMF molecules are inserted in the lattice without a bonding interaction. The magnetic susceptibility observed in the temperature interval 4.2 to 330K can be interpreted by means of a ³E ground term and D₂ as local symmetry, which was established by X-ray crystallography.     

Die Kristallstrukturen von {Li3(12-Krone-4)2[HC(CN)2]3}, {Na(15-Krone-5)-[HC(CN)2]} und {Na[N(nBu)4][HC(CN)2]2 · THF}

The Crystal Structures of {Li₃(12-crown-4)₂[HC(CN)₂]₃}, {Na(15-crown-5)[HC(CN)₂]}, and {NaN(nBu)₄[HC(CN)₂]₂ · THF} The preparation and the crystal structures of the title compounds 1 — 3 are described. 1 forms a polymeric chain structure, in which one of the lithium ions is linked by Li…NCC(H)CN… bridges. The remaining lithium ions form (12-crown-4)Li[NCC(H)CN] units, which are coordinated by one of the nitrogen atoms of the dicyanomethanide ions with the lithium ions of the chain. 2 forms an ion pair, in which the sodium ion is coordinated by the five oxygen atoms of the crown ether molecule and by one nitrogen atom of the dicyanomethanide ion. 3 has a threedimensional network, in which the sodium ions are coordinated in a distorted tetrahedral manner by the nitrogen atoms of the dicyanomethanide ions. In the cavities of the network the tetrabutylammonium ions and the THF molecules are found.     

Die Kristallstruktur von [TeCl3(15-Krone-5)]SbCl6

The Crystal Structure of [TeCl₃(15-crown-5)]SbCl₆ The title compound is synthesized by the reaction of tellur tetrachloride, 15-crown-5 and antimony pentachloride in acetonitrile solution, forming colourless crystals, which were characterized by IR spectroscopy and an X-ray structure determination. Space group Pnma, Z = 4, 1966 observed unique reflections, R = 0.072, R_w = 0.052. The compound forms ions [TeCl₃(15-crown-5)]⁺ and SbCl₆^?; in the cation the tellurium atom is eightfold coordinated by the three chlorine atoms and the five oxygen atoms of the crownether molecule (Te? O bond lengths 266 and 279 pm).     

(n‐Butyl­di­phenyl­phosphine)­di­chloro(η6‐p‐cymeme)­ruthenium(II)

The title ruthenium complex, [RuCl₂(C₁₀H₁₄)(C₁₆H₁₉P)], contains a monodentate (C₄H₉)PPh₂ ligand coordinated by the P atom. Coordination about the metal centre is completed by a η⁶‐p‐cymene ligand and two Cl atoms.     

[Bis(2‐diphenylphosphinoethyl) sulfide‐κ3P,S,P′](triphenylphosphine‐κP)platinum(II) diperchlorate acetone solvate

In the title compound, [Pt(C₁₈H₁₅P)(C₂₈H₂₈P₂S)]­(ClO₄)₂·­C₃H₆O or [Pt(PPh₃)(PSP)](ClO₄)₂·CH₃COCH₃, where PSP is the potentially tridentate chelate ligand bis(2‐di­phenyl­phosphinoethyl) sulfide, all three donor groups of the PSP ligand are coordinated to the central Pt atom, with Pt—P = 2.310 (1) Å and Pt—S = 2.343 (1) Å. The fourth coordination site is occupied by the P donor of the tri­phenyl­phosphine ligand [Pt—P = 2.289 (1) Å]. The complex cation has exact mirror symmetry, with the S atom, the Pt atom and the P atom of the PPh₃ ligand in the mirror plane. The Pt atom has a distorted square‐planar coordination geometry. A π–π interaction is present between the phenyl rings of the PPh₃ ligand and the terminal –PPh₂ group of the PSP chelate.     

K2[Mo2O4(C2O4)2(H2O)2]·3H2O

The crystal and molecular structure of dipotassium di‐μ‐oxo‐bis[aqua(oxalato‐O¹,O²)oxomolybdenum(III)] trihydrate, K₂­[Mo₂O₄(C₂O₄)₂(H₂O)₂]·3H₂O, has been determined from X‐ray diffraction data. In the dimeric anion, which has approximate twofold symmetry, each Mo atom is in a distorted octahedral coordination, being bonded to one terminal oxo‐O atom, two bridging O atoms, two O atoms from the oxalato ligand and one from the water mol­ecule. Bond lengths trans to the multiple‐bonded terminal oxo ligand are larger than those in the cis position, confirming the trans influence as a generally valid rule.     

Technetium Complexes with 2‐Mercapto‐methyltetrazolate

2‐Mercapto‐methyltetrazolate, Smetetraz^–, acts as monoanionic, monodentate ligand in a number of technetium compounds. Anionic Tc^V complexes of the types [TcO(Smetetraz)₄]^– and [TcN(Smetetraz)₄]^2– are formed when (Bu₄N)[Tc^VOCl₄] or (Bu₄N)[Tc^VINCl₄], respectively, react with Na(Smetetraz). Reduction of the metal takes place in the latter case. (Bu₄N)₂[TcN(Smetetraz)₄] crystallises in the monoclinic space group Pc (a = 9.701(5), b = 17.570(5), c = 16.821(10) Å, β = 96.50(3)°, Z = 2). The Tc atom is situated 0.580(3) Å above the basal plane of a square pyramid which is formed by the sulfur atoms and the nitrido ligand as its apex. The Tc–S bond lengths lie between 2.384(3) and 2.410(3) Å. [Tc(PPh₃)(Smetetraz)₃(CH₃CN)] is formed during the reaction of [TcCl₃(PPh₃)₂(CH₃CN)] with NaSmetetraz as blue needles with co‐crystallised solvent toluene (space group C2/c, a = 24.188(4), b = 14.373(1), c = 25.617(5) Å, β = 109.48(1)°, Z = 8). The metal atom is coordinated by PPh₃ and CH₃CN in the axial position of a trigonal bipyramid. All three aryl rings are on the sterically less strained side of the plane defined by the sulfur atoms. The Tc–S bond lengths range between 2.233(2) and 2.247(2) Å.     

Synthesis,chemical characterization,X-ray crystal structure and magnetic properties of oxalato-bridged copper(II) binuclear complexes with 2,2′-bipyridine and diethylenetriamine as peripheral ligands

Two new μ-oxalato binuclear copper(II) complexes, [{Cu(NO₃)(H₂O)(bipy)}₂(ox)] (1) and [{Cu(dien)}₂(ox)](NO₃)₂ (2), with ox=oxalate, dien=diethylenetriamine and bipy=2,2′-bipyridine, have been synthesized and their crystal and molecular structures have been determined by single-crystal X-ray diffraction methods. The crystal structure of 1 consists of centrosymmetric neutral dimers where the copper atoms lie in a strongly elongated octahedral environment, surrounded by two nitrogen atoms of a bipy molecule and two oxygen atoms of the bridging oxalato group in the equatorial plane and oxygen atoms of water molecules and nitrate ions in the axial positions. Crystal structure of 2 is made up of non-coordinated nitrate anions and asymmetric binuclear cations in which copper atoms are in a distorted square–pyramidal coordination with three atoms of a diethylenetriamine ligand and an oxygen atom of the asymmetrically coordinated oxalato bridge building the basal plane and the other oxygen atom of the oxalato ligand filling the apical position. Both compounds have been also characterized by Fourier transform infrared (FT-IR) and electron spin resonance (ESR) spectroscopies, thermal analysis and variable temperature magnetic susceptibility measurements. The two compounds exhibit antiferromagnetic exchange with a singlet–triplet separation of −382 and −6.5 cm⁻¹ for 1 and 2, respectively. Magnetic and ESR results are discussed with respect to the crystal structure of the compounds.     

The crystal structure of NaAs4O6Br

The crystal structure of NaAs₄O₆Br [a = 5.237(1), B = 8.043(1), C = 18.978(2) Å; space group Pmcn-D¹⁶_2h; Z = 4] was solved by a direct method strategy and was refined to an R value of 0.038 for 1515 intensities and 68 variables. The structure is characterized by neutrally charged and slightly waved As₂O₃ sheets arranged parallel to (001). These sheets are combined by the Na and Br atoms. The Na atom is coordinated to nine oxygen atoms and one bromine atom and the Br atom is coordinated to six arsenic atoms and one sodium atom. The compound NaAs₄O₆Br was synthesized by thermal treatment of NaBr and As₂O₃ in methanol solution [400(5) K, saturation vapor pressure].     

(PPh4)3Ag[WF5(C2I2)]2; synthese,IR-spektrum und kristallstruktur

The compound (PPh₄)₃Ag[WF₅(C₂I₂)]₂ is formed by the reaction of PPh₄[WCl₅(C₂I₂)] with an excess of silver fluoride in acetonitrile. The compound is soluble in CH₂Cl₂; when CCl₄ is added single red crystals are obtained. The complex is characterized by its IR spectrum and by an X-ray structural study (4060 observed, independent reflexions, R = 0.105). Crystal data: orthorhombic, space group P2₁2₁2, Z = 2, a 4464(2), b 1074(1), c 777,6(4) pm. The compound consists of PPh₄⁺ and Ag⁺ ions, and the anions [WF₅(C₂I₂)]²⁻, in which the tungsten atoms are seven-coordinated by five fluorine atoms and two carbon atoms. The diiodoacetylene ligand is symmetrically bonded sideways to the tungsten atom. The four equatorial F atoms have WF bond lengths of 191 pm, whereas the fluorine atom in trans-position to the WC₂ group is located 199 pm from the metal centre. The PPh₄⁺ ions are stacked in parallel columns.     

(PPh4)2[(SN)ReCl3(μ‐N)(μ‐NSN)ReCl3(THF)] – ein Nitrido‐Thionitrosyl‐Dinitridosulfato‐Komplex des Rheniums

(PPh₄)₂[(SN)ReCl₃(μ‐N)(μ‐NSN)ReCl₃(THF)] – a Nitrido‐Thionitrosyl‐Dinitridosulfato‐Complex of Rhenium The title compound has been prepared from PPh₄[Re^VIICl₄(NSCl)₂] with excess N(SiMe₃)₃ in dichloromethane solution to give red‐brown single crystals after recrystallisation from acetonitrile/THF solutions. As a by‐product PPh₄[ReNCl₄] is formed. (PPh₄)₂[(SN)ReCl₃(μ‐N)(μ‐NSN)ReCl₃(THF)] ( 1 ): Space group P2₁/n, Z = 4, lattice dimensions at –80 °C: a = 1024.1(1), b = 2350.2(1), c = 2315.4(2) pm, β = 94.09(1)°, R₁ = 0.0403. In the complex anion of 1 the rhenium atoms are connected by an asymmetric Re≡N–Re bridge as well as by a (NSN)^4–‐bridge to form a planar Re₂N(NSN) six‐membered heterocycle. Both rhenium atoms are coordinated by three chlorine atoms, one of them by a thionitrosyl ligand, the other one by the oxygen atom of a thf molecule.     

M+(12-crown-4) supramolecular cations (M+ = Na+, K+, Rb+, and NH4+) within Ni(2-thioxo-1,3-dithiole-4,5-dithiolate)2 molecular conductor

Monovalent cations (M+ = Na+, K+, Rb+, and NH4+) and 12-crown-4 were assembled to new supramolecular cation (SC+) structures of the M+(12-crown-4)n (n = 1 and 2), which were incorporated into the electrically conducting Ni(dmit)2 salts (dmit = 2-thioxo-1,3-dithiole-4,5-dithiolate). The Na+, K+, and Rb+ salts are isostructural with a stoichiometry of the M+(12-crown-4)2[Ni(dmit)2]4, while the NH4+ salt has a stoichiometry of NH4+(12-crown-4)[Ni(dmit)2]3(CH3CN)2. The electrical conductivities of the Na+, K+, Rb+, and NH4+ salts at room temperature are 7.87, 4.46, 0.78, and 0.14 S cm-1, respectively, with a semiconducting temperature dependence. The SC+ structures of the Na+, K+, and Rb+ salts have an ion-capturing sandwich-type cavity of M+(12-crown-4)2, in which the M+ ion is coordinated by eight oxygen atoms of the two 12-crown-4 molecules. On the other hand, the NH4+ ion is coordinated by four oxygen atoms of the 12-crown-4 molecule. Judging from the M(+)-O distances, thermal parameters of oxygen atoms, and vibration spectra, the thermal fluctuation of the Na+(12-crown-4)2 structure is larger than those of K+(12-crown-4)2 and Rb+(12-crown-4)2. The SC+ unit with the larger alkali metal cation gave a stress to the Ni(dmit)2 column, and the SC+ structure changed the pi-pi overlap mode and electrically conducting behavior.     

Kronenetherkomplexe von Blei(II). Die Kristallstrukturen von [PbCl(18-Krone-6)][SbCl6], [Pb(18-Krone-6)(CH3CN)3][SbCl6]2, and [Pb(15-Krone-5)2][SbCl6]2

Crown Ether Complexes of Lead(II). The Crystal Structures of [PbCl(18-Krone-6)][SbCl₆], [Pb(18-Krone-6)(CH₃CN)₃][SbCl₆]₂ und [Pb(15-Krone-5)₂][SbCl₆]₂ . [PbCl(18-crown-6)][SbCl₆] has been prepared in low yield besides [Pb(CH₃)₂(18-crown-6)][SbCl₆]₂ by the reaction of Pb(CH₃)₂Cl₂ with antimony pentachloride in acetonitrile solution in the presence of 18-crown-6, forming pale-yellow crystals. The other two title compounds are formed as colourless crystals by the reaction of PbCl₂ with antimony pentachloride in acetonitrile solutions in the presence of 18-crown-6 and 15-crown-5, respectively. The complexes were characterized by IR spectroscopy and by crystal structure determinations. [PbCl(18-crown-6)][SbCl₆]: Space group P2₁/c, Z = 8, 5 003 observed unique reflections, R = 0.046. Lattice dimensions at - 80°C: a = 1 386.9; b = 1 642.7; c = 2 172.1 pm, β = 92.95°. The lead atom in the cation [PbCl(18-crown-6)]⁺ is surrounded in an almost hexagonal-planar construction by the six oxygen atoms of the crown ether and an axially oriented Cl atom. [Pb(18-crown-6)(CH₃CN)₃][SbCl₆]₂: Space group P1 , Z = 2, 6 128 observed unique reflections, R = 0.076. Lattice dimensions at - 70°C: a = 1 228.0; b = 1 422.9; c = 1 463.2 pm, α = 69.08°; β = 65.71°; γ = 64.51°. In the cation [Pb(18-crown-6)(CH₃CN)₃]²⁺ the lead atom is coordinated by the six oxygen atoms of the crown ether and by the three nitrogen atoms of the acetonitrile molecules. The structure determination is restricted by disorder. [Pb( 15-crown-5)₂][SbCI₆]₂: Space group P6₃/m, Z = 6, 5 857 observed unique reflections, R = 0.059. Lattice dimensions at -70°C: a = b = 2 198.5; c = 1499.4 pm, α = β = 90°, γ = 120°. In the cation [Pb(l5-crown-5)₂]² the lead atom is sandwich-like coordinated by the ten oxygen atoms of the two crown ether molecules. The structure determination is restricted by disorder.     

Interaction of K2PdCl4 with aminoalkyldiphosphonic acids

Complexing of K₂PdCl₄ with 3-amino-1-hydroxypropylidene-1,1-diphosphonic acid (AHPDP) and 1-aminoethylidene-1,1-diphosphonic acid (AEDP) was studied by pH titration, spectrophotometry, and ³¹P NMR spectroscopy using metal to ligand mole ratios of 1: 1 and 1: 2. In equimolar complexes, AHPDP is coordinated to palladium(II) via two phosphonic oxygen atoms, whereas AEDP is coordinated via the amino nitrogen atom and a phosphonic oxygen atom. In the bisligand palladium(II) complex with AEDP, both ligand molecules are coordinated in a bidentate mode by the amino nitrogen atom and a phosphonic oxygen atom.     

(μ‐Oxalato‐O1,O2:O1′,O2′)bis[aqua(diethyl­enetri­amine)nickel(II)] bis(hexafluorophosphate) dihydrate

The title compound, [Ni₂(C₂O₄)(C₄H₁₃N₃)₂(H₂O)₂](PF₆)₂·‐2H₂O, contains a dinuclear oxalato‐bridged nickel(II) complex cation. The structure determination reveals the presence of a centrosymmetric binuclear complex where the oxalate ligand is coordinated in a bis­‐bidentate mode to the Ni atoms. The distorted octahedral environment of each Ni atom is completed by the three N atoms of the diethyl­enetri­amine ligand in a fac arrangement and by one O atom from a water mol­ecule. PF₆^? acts as counter‐anion. A two‐dimensional network of hydrogen bonds links the cations and anions and stabilizes the structure.     

Synthese und Kristallstruktur von [Ba(18-Krone-6)(DMF)4][Cd(Se4)2]

Synthesis and Crystal Structure of [Ba(18-Crown-6)(DMF)₄][Cd(Se₄)₂] The title compound has been prepared by the reaction of a DMF-solution of lithium polyselenide with BaSe₂ and cadmium acetate in the presence of 18-crown-6, forming black crystals. The compound was characterized by IR spectroscopy and by an X-ray structure determination. Space group P2/a, Z = 4, 5392 observed unique reflections, R = 0.048. Lattice dimensions at ?90°C: a = 2021.9(12); b = 1019.8(6); c= 2270.8(14)pm, ß = 106.98(4)°. The structure consists of [Ba(18-crown-6)(DMF)₄]²⁺ ions, in which the barium ions are coordinated by the six oxygen atoms of the crown ether molecule and by four oxygen atoms of the DMF molecules, and of [Cd(Se₄)₂]^2? ions. The cadmium atoms are coordinated by two tetraselenide ions in a chelating fashion.     

Synthesis,crystal structure,and vibrational spectrum of lithium <Emphasis Type="Italic">N</Emphasis>-(4′-benzo-15-crown-5)-5-bromo-2-hydroxyphenylaldiminatozinc perchlorate dihydrate

The synthesis, the IR absorption spectrum, and X-ray diffraction analysis of the complex [ZnLi(L¹)₂(H₂O)](ClO₄) · H₂O (I) (HL¹ = N-(4′-benzo-15-crown-5)-5-bromo-2-hydroxyphenylaldimine) are described. The crystals of I are monoclinic, a = 19.840(4) Å, b = 13.947(3) Å, c = 19.956(4) Å, β = 117.06(3)°, V = 4917.4(17) ų, Z = 4, space group P2₁/n, R = 0.0609 for 1409 reflections with I > 2σ(I). In the complex cation [ZnLi(L¹)₂(H₂O)]⁺, the Zn atom is bound to a distorted tetrahedral array of two N atoms (av. Zn-N, 2.027(10) Å) and two O atoms (av. Zn-O, 1.8968(8) Å) of two deprotonated L¹ ligands. The Li atom linked to the five ether oxygen atoms (av. Li-O_ether, 2.254(3) Å) sits atop the benzo-15-crown-5 (B15C5) macrocyclic plane of one coordinated L¹ ligand. The Li coordination is completed by water oxygen (Li-O(w1), 1.83(5) Å). The B15C5 cavity of the second coordinated ligand L¹ is vacant.     

Synthese und Kristallstruktur von [Na(12-Krone-4)2]2[Hg(Se4)2] · 1,5 DMF

Synthesis and Crystal Structure of [Na(12-Crown-4)₂]₂[Hg(Se₄)₂] · 1.5 DMF . The title compound has been prepared by the reaction of Na₂Se₄ with mercury acetate in DMF solution in the presence of 15-crown-5, forming dark red crystal needles. [Na(12-crown-4)₂]₂[Hg(Se₄)₂] · 1.5 DMF crystallizes in the space group C2/c with eight formula units per unit cell. The structure was determined with 3 824 observed unique reflections, R = 0.085. Lattice dimensions at - 70°C: a = 2 884(2), b = 1 407.7(7), c = 2 843(2) pm, β = 93.93(5)°. The structure consists of [Na(12-crown-4)₂]⁺ ions with a sandwichlike coordination of the crown ether molecules, and of [Hg(Se₄)₂]^2? ions, in which the mercury atom is coordinated by two tetraselenido ions in a chelating fashion. The [Hg(Se₄)₂]^2? ions are arranged to infinite chains via Se…?Se contacts.