Crystal structure of EuLnAgS<Subscript>3</Subscript> (Ln = Gd and Ho) compounds

The crystal structures of the first prepared EuLnAgS₃ (Ln = Gd and Ho) compounds, which have two polymorphs, were determined by X-ray powder diffraction. α-EuLnAgS₃ phases are isostructural to BaErAgS₃ (monoclinic crystal system, space group C2/m): a = 17.3168(10) Å, b = 3.9683(2) Å, c = 8.3174(4) Å, β = 103.94° (EuGdCuS₃); a = 17.1729(12) Å, b = 3.9367(3) Å, c = 8.2905(6) Å, β = 103.9° (EuHoCuS₃). β-EuLnAgS₃ phases belong to the AgBiS₂ structure type (cubic crystal system, space group Fm-3m): a = 5.739(2) Å (EuGdCuS₃) and a = 5.678 Å (EuHoCuS₃). In the α-EuLnAgS₃ crystal structure, LnS₆ octahedra and AgS₅ trigonal bipyramids share edges to form a three-dimensional (3D) structure with channels accommodating Eu²⁺ ions. A decrease in Ln³⁺ ionic radius gives rise to the crystal-chemical contraction of the 3D structure.     

Synthesis and structure investigation of Co(III) complex salts with the perrhenate anion

Complex salts of the composition [Co(NH₃)₆](ReO₄)₃·2H₂O (I), [Co(en)₃](ReO₄)₃ (II), [Co(NH₃)₅H₂O](ReO₄)₃·2H₂O (III), and [Co(NH₃)₅Cl](ReO₄)₂·0.5H₂O (IV) are obtained. Their crystal structures are determined by single crystal XRD. Crystallographic characteristics: (I) a = 9.9797(3) Å, b = 12.6994(3) Å, c = 14.7415(4) Å, β = 102.870(1)°, C2/c space group; (II) a = 8.0615(3) Å, b = 8.4483(4) Å c = 8.8267(4) Å, α = 61.923(2)°, β = 89.552(2)°, γ = 72.295(2)°, P1 space group; (III) a = 8.0086(4) Å, b = 12.9839(6) Å, c = 17.5122(7) Å, β=91.858(1)°, P2₁/n space group; (IV) a = 14.9446(3) Å, b = 14.6562(4) Å, c = 12.2434(4) Å, Cmc2₁ space group.     

Synthesis and structure of diethylenetriammonium tetrachloroaurates(III)

The (DienH₃)[AuCl₄]₃ · H₂O (I) and (DienH₃)₂[AuCl₄]Cl₅ (II) compounds were obtained by the reaction of HAuCl₄ with diethylenetriamine trihydrochloride (DienH₃Cl₃) in hydrochloric acid. The compounds were characterized by elemental analysis, X-ray diffraction, thermogravimetry, and IR spectroscopy. Crystals of I and II are monoclinic with space group P2₁/n. For I, a = 12.2314(3) Å, b = 14.6077(5) Å, c = 13.2680(5) Å, β = 106.7350(10)°, V = 2270.22(13) ų, Z = 8. For II, a = 6.62990(10) Å, b = 17.9026(5) Å, c = 10.3661(3) Å, β = 101.9230(10)°, V = 1203.83(5) ų, Z = 2. Both structures are ionic. The gold atoms in I and II have a 4 + 2 coordination environment. The Au-Cl bond lengths are within 2.276–2.294 Å, and the axial Au…Cl contacts are within 3.315–3.405 Å. The diethylenetriammonium cation in I and II has different conformations.     

Synthesis and study of ammonium decamolybdodimetallates

Ammonium decamolybdodimetallates (NH₄)_n[M₂Mo₁₀O₃₄(OH)₄] · 7H₂O, where M = Cr³⁺ (n = 6), Cu²⁺ (n = 8), or Ni²⁺ (n = 8), were synthesized for the first time and studied by X-ray diffraction, thermogravimetry, and IR spectroscopy. The compounds crystallize in the triclinic system with the following unit cell parameters: a = 10.68(2) Å, b = 9.46(2) Å, c = 7.97(2) Å, α = 75.12(3)°, β = 96.82(3)°, γ = 102.21(3)°, V = 754.4(3) ų, ρ_calcd = 4.05 g/cm³, Z = 1 for the chromium compound; and a = 10.57(2) Å, b = 9.29(2) Å, c = 8.47(2) Å, α = 73.91(3)°, β = 96.05(3)°, γ = 104.71(3)°, V = 854.3(3) ų, ρ_calcd = 3.68 g/cm³, Z = 1 (for the copper compound); and a = 10.96(2) Å, b = 8.95(2) Å, c = 7.40(2) Å, α = 71.76(3)°, β = 97.04(3)°, γ = 102.91(3)°, V = 875.3(3)ų, ρ_calcd = 3.65 g/cm₃, Z = 1 for the nickel compound.     

Structure of A Coordination Polymer [Cu(En)<Subscript>2</Subscript>CrO<Subscript>4</Subscript>]<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript>

The crystal structure of [Cu(En)₂CrO₄]_n (En is ethylenediamine) is determined: a = 14.7359(4) Å, b = 9.8083(3) Å, c = 14.2664(4) Å, V = 2061.98(10) ų, space group Cmce, Z = 8, d_x = 1.931 g/cm³. It is demonstrated that the studied phase is isostructural with [Сu(Еn)₂SO₄]_n. A pseudotetragonal copper atom coordination (Cu–N 2.0204 Å and 2.0244 Å, ∠N–Cu–N 84.73°) is completed to distorted octahedral by two oxygen atoms of chromate anions (Cu–O 2.433 Å and 2.380 Å).     

Hexa(isothiocyanato)chromates(III) of Some Yttrium Group Lanthanide(III) and Europium Complexes with Nicotinic Acid: Synthesis and Crystal Structures

Double ionic complexes [M(C₅H₅NCOO)₃(H₂O)₂][Cr(NCS)₆] · nH₂O, where M = Eu (I), n = 1.15; Dy (II), Er (III), n = 1.5; M = Yb (IV), n = 2, have been synthesized by the reaction between M(NO₃)₃, M = Eu, Dy, Er, Yb, K₃[Cr(NCS)₆], and nicotinic acid (C₅H₅NCOO) in an aqueous solution and studied by chemical analysis, IR spectroscopy, and X-ray diffraction. Crystals of complexes I–IV are monoclinic, space group P2₁/n, Z = 4; a = 9.5358(2) Å, b = 25.4871(5) Å, c = 15.4303(4) Å, β = 105.513(1)°, V = 3613.6(1) ų, ρ_calcd = 1.799 g/cm³ for I, a = 9.5901(5) Å, b = 25.8599(15) Å, c = 15.6316(9) Å, β = 106.829(2)°, V = 3710.6(4) ų, ρ_calcd = 1.782 g/cm³ for II, a = 9.5640(3) Å, b = 25.8936(11) Å, c = 15.6498(7) Å, β = 106.895(2)°, V = 3708.3(3) ų, ρ_calcd = 1.791 g/cm³ for III, and a = 9.5049(2) Å, b = 25.6378(4) Å, c = 15.5120(3) Å, β = 106.934(1)°, V = 3616.1(1) ų, ρ_calcd = 1.864 g/cm³ for IV.     

Synthesis and structure of bis(1,2-diaminoethane) copper(II) bis(<Emphasis Type="Italic">o</Emphasis>-hydroxybenzoate) monohydrate and <Emphasis Type="Italic">trans</Emphasis>-diaquabis(1,2-diaminoethane)copper(II) bis(<Emphasis Type="Italic">o</Emphasis>-aminobenzoate)

X-ray structural analysis has been performed for two complex compounds: Cu(en)₂(o-HB)₂H₂O (I) (a = 16.873(4) Å, b = 8.713(2) Å, c = 14.803(3) Å, β = 91.15(2)°, V = 2175.8(8) ų, C2/c, Z = 4, R(F) = 0.0263, 1516 reflections with I > 3σ (I)) and [Cu(en)₂(OH₂)₂]²⁺(o-AB^?)₂ (II) (a = 7.488(5) Å, b = 22.122(8) Å, c = 7.856(5) Å, β = 118.77(2)°, V = 1140.7(11) ų, P2₁/n, Z = 2, R(F) = 0.0432, 1684 reflections with I > 3σ(I)) synthesized under identical conditions (en is ethylenediamine, o-HB is o-hydroxybenzoate, and o-AB is o-aminobenzoate). Although the compounds were assumed to have similar structures and the Cu-Lig bond lengths and the cis and trans angles are acceptable for an octahedral structure, the geometric parameters of o-HB suggest that the copper atom has a plane square environment.     

Investigation of pentaamminechloroplatinum(IV) perrhenate dihydrate

The crystal structure of the [Pt(NH₃)₅Cl](ReO₄)₃·2H₂O salt is determined. Crystallographic data: a = 10.3476(2) Å, b = 12.8955(2) Å, c = 14.3536(3) Å, β = 105.241(10)°, V = 1847.94(6) ų, space group P ₂1/n, Z = 4, d _x = 3.962 g/cm³. Thermal decomposition of the compound is studied in a helium and hydrogen atmosphere. A two-phase product arises in the former case, in the latter a substitution Re_0.75Pt_0.25 solid solution with unit cell parameters: a = 2.767(2) Å, c = 4.441(3) Å, space group P6₃/mmc.     

Structure of Potassium and Cesium Barbiturates

The structures of catena-[K(μ₆-Hba?O,O,O,O′,O′,O″)] (I) and catena-[Cs(μ₆-Hba–O,O,O′,O′,O″,O″)] (II), where Н₂ba is barbituric acid C₄H₄N₂O₃, were characterized by powder X-ray diffraction. Crystallographic data: a = 14.1603 (4) Å, b = 3.68977 (9) Å, c = 10.9508 (3) Å, β = 82.226 (1)°, V = 566.90 (3) ų, space group P2₁/n, Z = 4 for I; a = 14.652 (1) Å, b = 11.7275 (7) Å, c = 3.8098 (3) Å, β = 79.140 (6)°, V = 642.90 (8) ų, space group C2/m, Z = 4 for II. The structural topologies of alkali metal complexes with barbituric acid and some its derivatives were compared. The thermal stability of complexes I and II in an air atmosphere was studied.     

Structure and properties of terbium(III) dipivaloylmethanate and its adducts with Bipy and Phen

The complex of terbium(III) with dipivaloylmethane (2,2,6,6-tetramethylheptane-3,5-dione = Htmhd) [Tb(tmhd)₃]₂ (1) and two its adducts with bipyridyl (Bipy) and phenanthroline (Tb(tmhd)₃·Bipy (2) and Tb(tmhd)₃·Phen (3)) are synthesized and analyzed by single crystal X-ray diffraction. The crystals of [Tb(tmhd)₃]₂ (1) belong to the monoclinic crystal system: P2₁/n space group, a = 12.2238(2) Å, b = 27.6369(5) Å, c = 21.8740(4) Å, β = 105.146(1)°, V = 7133.0(2)ų, Z = 4; the crystals of Tb(tmhd)₃·Bipy (2) and Tb(tmhd)₃·Phen (3) belong to the triclinic crystal system with unit cell parameters: (2) \(P\bar 1\) space group, a = 11.0554(6) Å, b = 12.2761(7) Å, c = 17.7096(8) Å, α = 77.457(2)°, β = 85.557(2)°, γ = 69.659(2)°, V = 2199.8(2) ų, Z = 2; (3) \(P\bar 1\) space group, a = 10.8814(3) Å, b = 12.2852(4) Å, c = 18.3590(6) Å, α = 80.463(1)°, β = 87.587(1)°, γ = 68.640(1)°, V = 2253.6(1) ų, Z = 2. The structures of the complexes are molecular and involve isolated [Tb₂(tmhd)₆] (1), Tb(tmhd)₃·Bipy (2), and Tb(tmhd)₃·Phen (3) molecules. The thermal properties of the obtained terbium complexes are studied by TG-DTA.     

Synthesis and structure of Pt(II) acetamidate complexes containing <Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-dimethyl-substituted ethylenediamine and trimethylenediamine

Reactions of acetamide with platinum(II) diamines [Pt(N,N-DimeEn)Cl₂], [Pt(Tm)Cl₂], and [Pt(N,N-DimeTm)Cl₂] (N,N-DimeEn = (CH₃)₂N(CH₂)₂NH₂, Tm = NH₂(CH₂)₃NH₂, N,N-DimeTm = (CH₃)₂N(CH₂)₃NH₂) with preliminary precipitation of chlorine ions by silver salts gave binuclear Pt(II) acetamidates [Pt₂(CH₃)₂N(CH₂)₂NH₂)₂(μ-NHCOCH₃)₂](NO₃)₂ · H₂O (I), [Pt₂(NH₂(CH₂)₃NH₂)₂)(μ-NHCOCH₃)₂](NO₃)₂ · H₂O (II), and [Pt₂(CH₃)₂N(CH₂)₃NH₂)₂(μ-NHCOCH₃)₂](HSO₄)₂ (III), whose crystal structures were determined. Crystals of I are monoclinic: a = 14.459(2) Å, b = 17.197(3) Å, c = 9.822(2) Å, β = 105.923(10)°, V = 3348.6(8) ų, space group P2(1)/c, Z = 4, R _hkl = 0.0419 for 6663 reflections. Complex I is a binuclear acetamidate with bridging (NHCOCH₃)^? ligands, one of which is bound to two Pt atoms through the N and O atoms, and the other ligand is bound only through the N atom. The Pt-Pt distance is 2.987(1) Å. Crystals of II are monoclinic: a = 10.213(7) Å, b = 13.373(9) Å, c = 16.533(11) Å, β = 97.971(9)°, V = 2236(3) ų, space group P2(1)/n, Z = 4, R _hkl = 0.557 for 6462 reflections. The Pt-Pt distance is 3.057(1) Å. Crystals of III are monoclinic: a = 10.557(12) Å, b = 18.531(2) Å, c = 14.4744(17) Å, β = 108.705(2)°, V = 2682(5) ų, space group P2(1)/n, Z = 4, R _hkl = 0.569 for 8506 reflections. The Pt-Pt distance is 3.202(1) Å. Complexes II and III are binuclear acetamidates, in which two chelating Pt(Tm) or Pt(N,N-DimeTm) moieties are coordinated through the N and O atoms of (NHCOCH₃)^? cis-bridges.     

Crystal structure and properties of [M(NH<Subscript>3</Subscript>)<Subscript>5</Subscript>Cl](NO<Subscript>3</Subscript>)<Subscript>2</Subscript>, (M = Ir,Rh, Ru)

The crystal structures of compounds from the series [M(NH₃)₅Cl](NO₃)₂, (M = Ir, Rh, Ru) were described. The compounds crystallized in the tetragonal crystal system, space group I4, Z = 2. Crystal data for [Ir(NH₃)₅Cl](NO₃)₂ (I): a = 7.6061(1) Å, b = 7.6061(1) Å, c = 10.4039(2) Å, V = 601.894(16) ų, ρ_calc = 2.410 g/cm³, R = 0.0087; [Rh(NH₃)₅Cl](NO₃)₂ (II): a = 7.5858(5) Å, b = 7.5858(5) Å, c = 10.41357(7) Å, V = 599.24(7) ų, ρ_calc = 1.926 g/cm³, R = 0.0255; [Ru(NH₃)₅Cl](NO₃)₂ (III): a = 7.5811(6) Å, b = 7.5811(6) Å, c = 10.5352(14) Å, V = 605.49(11) ų, ρ_calc = 1.896 g/cm³, R = 0.0266. The compounds were defined by IR spectroscopy and XRPA and thermal analyses.     

Crystal Structure of <Emphasis Type="Italic">DL</Emphasis>-Valinium Tetrafluoroantimonate(III) Monohydrate

The crystal structure of an antimony(III) fluoride complex of the composition (C₅H₁₂NO₂)SbF₄·H₂O (I) involving a cation of α-amino isovaleric acid (DL-valine, Val) is determined. Crystals are monoclinic: a = 12.2024(2) Å, b = 6.1636(1) Å, c = 15.5167(3) Å, Z = 4, space group P2₁/c. The structure is formed of DL-valinium (C₅H₁₂NO₂)⁺ cations, complex [SbF₄]_n^n? anions having a polymeric chain structure, and crystallization water molecules. The [SbF₄]_n^n? complex anions consist of trigonal SbF4E bipyramids joined together by asymmetric bridging Sb–F(3)···Sb bonds. The structural units are organized into a threedimensional framework via N–H···F, N–H···O, and O–H···F hydrogen bonds.     

Synthesis and Crystal Structure of Dinitratotetra(hexamethylphosphoric Triamide)-Lanthanum(III)Tetra(Isothiocyanato)Diammine Chromate(III)

A new coordination compound having the formula [La(HMPA)₄(NO₃)₂][Cr(NH₃)₂(NCS)₄] (I), where HMPA is ((CH₃)₂N)₃PO, has been synthesized and studied by X-ray diffraction. Studied crystals of compound I are monoclinic, space group P2₁/n, a = 15.0360(3) Å, b = 15.1214(3) Å, c = 26.7529(7) Å, β = 100.6610(10)°, V = 5977.7(9) Å3, Z = 2, ρ_calc = 1.442 g/cm³, and R₁ = 0.0453 for 7344 reflections with F_o ≥ 4σ(F_o).     

Structure and properties of the volatile isomers of bis(1,1,1-trifluoro-5,5-dimethylhexane-2,4-dionato) of platinum(II)

In the work, isomeric complexes of platinum(II) with the (ptac)^–1 pivaloyltrifluoroacetonate ion (Pt((CH₃)₃–CO–CH–CO–CF₃)₂) are studied. The synthesis and chromatographic separation of Pt(ptac)₂ isomers are described, TGA data for the separated isomers are given, and the crystal structures of the solid phases are studied. The cis-Pt(ptac)₂ complex crystallizes in the space group P-1, a = 10.7091(4) Å, b = 12.7787(6) Å, c = 16.0154(8) Å, α = 92.389(2)°, β = 90.868(2)°, γ = 112.1260(10)°, V = 2027.39(16) ų, Z = 4, d _calc = 1.918 g/cm³. The trans-Pt(ptac)₂ complex crystallizes in the space group C2/m, a = 13.3235(5) Å, b = 8.5515(3) Å, c = 9.6694(3) Å, β = 118.5880(10)°, V = 967.38(6) Å3, Z = 2, d _calc = 2.010 g/cm3. The structures of the complexes are molecular, the Pt atom has a square coordination of four oxygen atoms of two ligands; for cis-Pt(ptac)2, the Pt–Oav distance is 1.968 Å, for trans-Pt(ptac)2 it is 1.980 Å.     

Synthesis and crystal structures of two silver(I) complexes derived from 2-amino-6-methylpyridine with nicotinic acid and isonicotinic acid

The reaction of Ag₂O and 2-amino-6-methylpyridine (AMP) with nicotinic acid (HNA) and isonicotinic acid (HINA), respectively, afforded two silver(I) complexes, [Ag₂(NA)₂(AMP)₂] _n (I) and [Ag₂(INA)₂(AMP)₂] _n (II). Both complexes were characterized by elemental analyses and X-ray single-crystal diffraction. Complex I is a pyridine-3-carboxylate bridged polynuclear silver(I) complex, in which the Ag atom is in a tetrahedral geometry, while complex II is a pyridine-4-carboxylate bridged polynuclear silver(I) complex, in which the Ag atom is in a distorted T-shaped geometry. The crystal of I is monoclinic: space group P2₁/c, a = 8.079(2), b = 17.150(3), c = 8.912(2) Å, β = 98.106(2)°, V = 1222.5(5) ų, Z = 4. The crystal of II is monoclinic: space group P2₁/c, a = 7.225(1), b = 12.049(1), c = 15.053(2) Å, β = 102.050(1)°, V = 1281.6(3) ų, Z = 4.     

X-ray diffraction study of the monoclinic modification of [Cu(NH<Subscript>3</Subscript>)<Subscript>4</Subscript>](ReO<Subscript>4</Subscript>)<Subscript>2</Subscript> in the range 100-410 K

The monoclinic modification of [Cu(NH₃)₄](ReO₄)₂ complex salt in the range 100-410 K is studied by single crystal X-ray diffraction. The crystallographic data for 300 K are as follows: a = 10.6123(3) Å, b = 7.5443(2) Å, c = 15.2261(4) Å, β = 108.406(1)°, V = 1156.67(5) ų, space group Р2₁/n, Z = 4, d_x = 3.623 g/cm³. The coordination environment of the Cu atom, being a distorted square formed by four nitrogen atoms with Cu–N of 1.997-2.018 Å, is completed by the contacts with two oxygen atoms Cu…O of 2.472 Å and 2.598 Å. The comparative crystal chemical analysis with the triclinic modification of [Cu(NH₃)₄](ReO₄)₂ known in the literature is performed.     

Mononuclear cobalt (III) complexes with <Emphasis Type="Italic">N</Emphasis>-salicylidene-2-hydroxy-5-bromobenzylamine and <Emphasis Type="Italic">N</Emphasis>-salicylidene-2-hydroxy-5-chlorobenzylamine

Cobalt (III) complexes with N-salicylidene-2-hydroxy-5-bromobenzylamine (H₂sbba) and N-salicylidene-2-hydroxy-5-chlorobenzylamine (H₂scba), [n-(C₄H₉)₄N][Co(sbba)₂] (I) and [n-(C₄H₉)₄N][Co(scba)₂] (II), were synthesized. The crystal structure of II was determined by the single-crystal X-ray diffraction method at 90 K confirming its crystallization in the monoclinic space group P2₁/n with a = 11.729(2) Å, b = 16.901(3) Å, c = 21.483(4) Å, β = 98.840(4)°, V = 4208.2(14) ų, D_x = 1.295 g cm^?3, and Z = 4. The R1 [I > 2σ(I)] and wR2 (all data) values of 0.0664 and 0.1920, respectively, for all 9521 independent reflections. The compound is composed of a tetra(n-butyl)ammonium cation and an octahedral cobalt(III) complex anion with two scba^2? ligands in a meridional fashion. The electronic spectral features of I and II are consistent with the octahedral cobalt(III) ion with an N₂O₄ donor set.     

Structural investigation of salts containing ions [Pd(NH<Subscript>3</Subscript>)<Subscript>4</Subscript>]<Superscript>2+</Superscript> and [IrF<Subscript>6</Subscript>]<Superscript>2–</Superscript>

Double complex salts (DCS) α-[Pd(NH₃)₄][IrF₆]·H₂O (P2₁/m, a = 6.3181(3) Å, b = 10.8718(5) Å, с = 7.4526(4) Å, β = 103.568(2)°), β-[Pd(NH₃)₄][IrF₆]·H₂O (P2₁/с, a = 8.5773(3) Å, b = 10.8791(4) Å, с = = 12.6741(3) Å, β = 122.497(2)°), [Pd(NH₃)₄]₃[IrF₆]₂Cl₂·H₂O (P-1, a = 7.6080(2) Å, b = 7.6274(2) Å, с = 11.8070(3) Å, β = 122.497(2)°), and [Pd(NH₃)₄]₂[IrF₆]NO₃ (Fm-3m, a = 11.21210(10) Å) have been synthesized and structurally characterized for the first time. The existence of polymorphs for the DCS has been revealed. The influence of the chemical composition of the initial reagents on the reaction course and, respectively, the products, has been demonstrated. A hypothesis on the influence of the second coordination sphere on the formation of one or the other polymorph of the DCS has been suggested. It has been shown that the series α-[Pd(NH₃)₄][МF₆]·H₂O (M = Pt, Pd) exhibits isostructurality.     

Crystal structures of tetrafluoroantimonates(III) of single and double protonated 3-amino-1,2,4-triazolium cations

Crystal structures are determined by X-ray crystallography for tetrafluoroantimonates(III) of single and double protonated 3-amino-1,2,4-triazolium cations of the composition (C₂H₅N₄)SbF₄ (I) (monoclinic: a = 4.7723(6) Å, b = 19.643(2) Å, c = 7.6974(9) Å, β = 97.239(2)°, Z = 4, Cc space group) and (C₂H₆N₄)(SbF₄)₂ (II) (monoclinic: a = 4.7617(3) Å, b = 15.512(1) Å c = 7.4365(5)Å β = 107.706(1)°, Z = 2, P2₁/n space group). The structure of I is built from complex [SbF₄]^? anions and single charged (C₂H₅N₄)⁺ cations; the structure of II is built from the same anion and double charged 3-amino-1,2,4-triazolium cation: (C₂H₆N₄)²⁺. In the structure, weak interactions Sb…F join the anions in polymeric layers [SbF₄] _n ^n? that are assembled in a 3D framework by N-H…F hydrogen bonds. The formation of the double protonated 3-amino-1,2,4-triazolium cation (C₂H₆N₄)²⁺, found in the crystal structure of II, is observed for the first time.