Hydroxylammonium fluorometalate: synthesis and characterisation of a new fluorozincate

Abstract  

A new coordination compound of zinc fluoride and hydroxylammonium, (NH₃OH)₂ZnF₄, was obtained after dissolving zinc powder in hydrofluoric acid (40%) and adding solid hydroxylammonium fluoride. The colourless crystals were characterised chemically, magnetically, structurally by single-crystal X-ray diffraction analysis, and thermogravimetrically by TGA and DSC analysis. The structure consists of NH₃OH⁺ cations and ZnF₆ octahedra in which the metal ion lies on the inversion centre. Each of the ZnF₆ octahedra shares four of its vertices in a way that each vertex is shared between two octahedra. Oxygen and nitrogen atoms of hydroxylammonium cations are donors of hydrogen bonds. Hydroxylamonium fluorozincate crystallizes monoclinic, P21/c, with cell parameters a = 8.1604(4) ?, b = 5.8406(3) ?, c = 5.6586(2) ? and β = 94.745(3)°. The compound decomposes above 373 K in four steps, obtaining ZnO as the final residue. Magnetic properties of the compound were studied between 2 and 300 K, giving the prevailing diamagnetic behaviour with room temperature susceptibility of −9 × 10⁻⁵ emu mol⁻¹.     

Untersuchungen der Hydroxylammonium-Aluminate

Summary Two microcristalline phases have been isolated from aqueous solutions: (NH₃OH)₂AlF₅(A) and (NH₃OH)AlF₄·H₂O(B). They crystallize in the orthorhombic system with cell parameters for A:a=6.475 (3) Å,b=7.295 (3) Å,c=10.827 (5) Å, and for B:a=7.003 (3) Å,b=8.489 (4) Å,c=10.745 (5) Å. The Hydroxylammonium-aluminates were characterized by vibrational spectroscopy and their thermal decomposition studied by DSC and TG analysis.

     

Dissolving the insoluble: CdF<Subscript>2</Subscript> and moist ammonia form cadmium(II) difluoride monohydrate—synthesis and crystal structure of [Cd(NH<Subscript>3</Subscript>)<Subscript>6</Subscript>]F<Subscript>2</Subscript>·H<Subscript>2</Subscript>O

Abstract  

Hexaamminecadmium(II) fluoride monohydrate (1:1) [Cd(NH₃)₆]F₂·H₂O was synthesized from CdF₂ and liquid ammonia in open reaction vessels, so that moisture from the air was in contact with the solvent. The compound crystallizes in the chiral space group P3₁21- (No. 152) in the form of needle-shaped, colorless crystals with a = 6.8974(1) ?, c = 17.7156(5) ?, V = 729.89(3) ?³, and Z = 3.     

Two New Dawson-Type Polyoxometalates: 1D Chain Made by Mono-Dawson Units and 2D Layer Made by Double-Dawson Units

Abstract  

Two new Dawson-Type POTs, (H₂en)H₂[Cu(en)₂][Cu(en)(H₂O)₃][Cu(en)₂ (H₂O)](P₂W₁₇CuO₆₁)·8H₂O (1, en = ethylenediamine) and H₁₀K₆(P₂W₁₇CuO₆₁)₂·34H₂O (2), have been synthesized under hydrothermal conditions and characterized by IR spectroscopy, TG, XRD and single-crystal X-ray structural analysis. Crystal data for 1: triclinic, P[`1] {P}{\bar{1}} , a = 11.6855(26) ?, b = 13.2679(29) ?, c = 28.1540(60) ?, α = 80.4009(75)°, β = 82.5150(79)°, γ = 67.1482(46)°, Z = 2. Crystal data for 2: monoclinic, C2/c, a = 43.5701(99) ?, b = 12.3078(25) ?, c = 29.3742(66) ?, β = 101.3749(21)°, Z = 4. Compound 1 exhibits a 1D chain, in which the [Cu(en)₂]²⁺ cations act as the linkages of mono-{P₂W₁₇Cu} units. Compound 2 shows a 2D layer, in which the double-Dawson units are connected by K⁺ cations.     

Evidence of quasi-intramolecular redox reactions during thermal decomposition of ammonium hydroxodisulfitoferriate(III), (NH4)2[Fe(OH)(SO3)2]·H2O

Synthesis of ammonium hydroxodisulfitoferriate(III), (diammonium catena-{bis(μ ²-sulfito-κO,κO)-μ ²-hydroxo-κ²O}ferrate(III) monohydrate) (NH₄)₂[Fe(OH)(SO₃)₂]·H₂O (compound 1) and its thermal behavior is reported. The compound is stable in air. Its thermal decomposition proceeds without the expected quasi-intramolecular oxidation of sulfite ion with ferric ions. The disproportionation reaction of the ammonium sulfite, formed from the evolved NH₃, SO₂ and H₂O in the main decomposition stage of 1, results in the formation of ammonium sulfate and ammonium sulfide. The ammonium sulfide is unstable at the decomposition temperature of 1 (150 °C) and transforms into NH₃ and H₂S which immediately forms elementary sulfur by reaction with SO₂. The formation and decomposition of other intermediate compounds like (NH₄)₂S_nO_x (n = 2, x = 3 and n = 3, x = 6) results in the same decomposition products (S, SO₂ and NH₃). Two basic iron sulfates, formed in different ratios during synthesizing experiments performed under N₂ or in the presence of air, have been detected as solid intermediates which contain ammonium ions. The final decomposition product was proved to be α-Fe₂O₃ (mineral name hematite).

     

Strukturen und thermische Zersetzung von enH2(H3O)[AlF6] und enH2[AlF5(H2O)]

Structures and Thermal Decomposition of enH₂(H₃O)[AlF₆] and enH₂[AlF₅(H₂O)] By precipitation with ethylene diamine (en) from a hydrofluoric acid solution of aluminium enH₂(H₃O)[AlF₆] is formed. It crystallizes in the orthorhombic space group Pnma, a = 1084.9(1), b = 1079.4(1), c = 682.0(1) pm, R = 0.032. H₃O⁺ cations and [AlF₆]^3– anions are connected via strong H bonds to layers which are further linked to a 3 D network by H bonds from the enH₂²⁺ cations. By recrystallization from water or precipitation from a less acid solution enH₂[AlF₅(H₂O)] is formed, which crystallizes monoclinic in the space group P2₁ (a = 660.0(1), b = 563.5(1), c = 994.4(2) pm, β = 98.44(3)°, R = 0.029). The [AlF₅(H₂O)]^2– anions are linked by strong O–H…F bonding to form ‘einer-double chains' interconnected again via the enH₂²⁺ cations to a 3 D framework. Thermoanalytical investigations show that enH₂[AlF₅(H₂O)], by loss of water above 150 °C, as well as enH₂(H₃O)[AlF₆], by loss of water and HF above 120 °C, transform to enH₂AlF₅. The subsequent decomposition goes over NH₄⁺ containing intermediates towards β-AlF₃. Before decomposition the oxonium fluoroaluminate reveals a reversible phase transition at 99 °C.     

Structure of a new compound synthesized by microwave heating: [H3N(CH2)6NH3)]·AlF5

A new hybrid material was synthesized by the microwave route from a mixture of Al₂O₃/HF/1,6 diaminohexane/EtOH. The structure of the hybrid fluoroaluminate, determined by single crystal X-ray diffraction, reveals a [H₃N(CH₂)₆NH₃]·AlF₅ formulation and a monoclinic symmetry with the space group P2₁, with a=7.898(1) Å, b=5.514(1) Å, c=12.672(3) Å, β=103.69(2)°, V=536.2(2) ų and Z=2. The unit cell contains infinite inorganic chains of [AlF₆] corner-sharing octahedra, linked each other by hexanediammonium cations.     

Preparation, Thermal Behaviour, and Crystal Structure of MgAl2F8(H2O)2

 Single crystals of MgAl₂F₈(H₂O)₂ have been obtained under hydrothermal conditions (250°C, 14 d) from a starting mixture of AlF₃ and MgAlF₅(H₂O)₂ in a 5% (w/w) HF solution. The crystal structure has been determined and refined from single crystal data (Fmmm (#69), Z = 4, a = 7.2691(7), b = 7.0954(16), c = 12.452(2) ?, 281 structure factors, 27 parameters, R(F ² > 2σ (F ²)) = 0.0282, wR(F ² all) = 0.0885). The obtained crystals were systematically twinned according to (010/100/001) as twinning matrix, reflecting the pseudo-tetragonal metric. The crystal structure is composed of perowskite-type layers built of corner sharing AlF₆ octahedra with an overall composition of AlF₄ ⁻ which are connected via common fluorine atoms of [MgF_4/2(H₂O)_2/1] octahedra. Group-subgroup relations of MgAl₂F₈(H₂O)₂ to WO₃(H₂O)_0.33 and to other M(II)M(III)₂ F₈(H₂O)₂ structures are briefly discussed. Above 570°C, MgAl₂F₈(H₂O)₂ decomposes under elimination of water into α-AlF₃, β-AlF₃, and MgF₂.     

A novel mononuclear square-planar copper(II) complex (Pip-H+)2[CuL4]2? with 2-cyano-3-(2,5-dimethoxyphenyl)acrylic acid as ligand: synthesis, crystal structures, spectral and thermal studies

Abstract  

2-Cyano-3-(2,5-dimethoxyphenyl)acrylic acid and its novel mononuclear square-planar copper(II) complex dipiperidinium tetrakis[2-cyano-3-(2,5-dimethoxyphenyl)acrylic acid]copper(II) ((Pip-H⁺)₂[CuL₄]²⁻) were synthesized and characterized by elemental analyses, FT–IR, UV–Vis spectroscopy, and thermogravimetric analysis. Moreover, the ligand was characterized by ¹H and ¹³C NMR spectroscopy. The structures of the ligand and its copper(II) complex were confirmed by single-crystal X-ray crystallography. Whereas the ligand crystallizes in the triclinic space group Pī with unit cell parameters a = 4.6911(2) ?, b = 9.0181(4) ?, c = 13.7084(6) ?, α = 74.946(4)°, β = 87.152(4)°, γ = 89.220(4)°, V = 559.34(4) ?³, and Z = 2, the complex crystallizes in the orthorhombic space group Pccn with unit cell parameters a = 27.5486(5) ?, b = 12.9484(2) ?, c = 15.8822(3) ?, V = 5,665.34(17) ?³, and Z = 4.     

Bismuth flux crystal growth of RERh6P4 (RE?=?Sc, Yb, Lu): new phosphides with a superstructure of the LiCo6P4 type

Abstract  

The rhodium-rich phosphides RERh₆P₄ (RE = Sc, Yb, Lu) were synthesized from the constituent elements in bismuth fluxes and their structures were refined from X-ray single-crystal diffractometer data: P3, a = 6.968(2), c = 3.666(2) ?, wR (F ²) = 0.0481, 895 F ² for ScRh₆P₄; a = 6.971(1), c = 3.673(1) ?, wR (F ²) = 0.0614, 700 F ² for YbRh₆P₄; a = 6.971(2), c = 3.682(1) ?, wR (F ²) = 0.0828, 722 F ² for LuRh₆P₄ with 37 variables per refinement. All three crystals are twinned. The twinning and the structural relationship with the aristotype LiCo₆P₄, space group P[`6]m2P\bar 6m2 are discussed on the basis of a group–subgroup scheme. The RERh₆P₄ phosphides belong to the large number of metal-rich compounds with a metal-to-phosphorus ratio near 2:1. The isolated phosphorus atoms have trigonal prismatic metal coordination by RE and Rh atoms. The high rhodium content leads to a pronounced rhodium substructure (278–293 pm Rh–Rh in ScRh₆P₄). From a geometrical point of view, the RERh₆P₄ structures can be viewed as intergrowth variants of slightly distorted ThCr₂Si₂-related slabs as realized for KRh₂P₂.     

Phase equilibria in binary subsystems of urea–biuret–water system

Joint results of the differential scanning calorimetry (DSC) and thermogravimetry (TG) experiments were the basis for the fusion enthalpy and temperature determination of the biuret (NH₂CO)₂NH (synthesis by-product of the urea fertilizer (NH₂)₂CO). Recommended values are Δ_m H = (26.1 ± 0.5) kJ mol⁻¹, T _m = (473.8 ± 0.4) K. The DSC method allowed for the phase diagrams of “water–biuret,” “water–urea,” “urea–biuret” binary systems to be studied; as a result, liquidus and solidus curves were precisely defined. Stoichiometry and decomposition temperature of the biuret hydrate identified, composition of the compound in “urea–biuret” system was suggested.     

Preparation,Thermal Behaviour,and Crystal Structure of MgAl<Subscript>2</Subscript>F<Subscript>8</Subscript>(H<Subscript>2</Subscript>O)<Subscript>2</Subscript>

Summary.  Single crystals of MgAl₂F₈(H₂O)₂ have been obtained under hydrothermal conditions (250°C, 14 d) from a starting mixture of AlF₃ and MgAlF₅(H₂O)₂ in a 5% (w/w) HF solution. The crystal structure has been determined and refined from single crystal data (Fmmm (#69), Z = 4, a = 7.2691(7), b = 7.0954(16), c = 12.452(2) ?, 281 structure factors, 27 parameters, R(F ² > 2σ (F ²)) = 0.0282, wR(F ² all) = 0.0885). The obtained crystals were systematically twinned according to (010/100/001) as twinning matrix, reflecting the pseudo-tetragonal metric. The crystal structure is composed of perowskite-type layers built of corner sharing AlF₆ octahedra with an overall composition of AlF₄ ⁻ which are connected via common fluorine atoms of [MgF_4/2(H₂O)_2/1] octahedra. Group-subgroup relations of MgAl₂F₈(H₂O)₂ to WO₃(H₂O)_0.33 and to other M(II)M(III)₂ F₈(H₂O)₂ structures are briefly discussed. Above 570°C, MgAl₂F₈(H₂O)₂ decomposes under elimination of water into α-AlF₃, β-AlF₃, and MgF₂. Received October 29, 2001. Accepted (revised) December 6, 2001     

Hydrolysis behavior of a precursor for bridged polysilsesquioxane 1,4-bis(triethoxysilyl)benzene: a <Superscript>29</Superscript>Si NMR study

The hydrolysis behavior of 1,4-bis(triethoxysilyl)benzene (BTB), a precursor of bridged polysilsesquioxane, was investigated with high-resolution ²⁹Si nuclear magnetic resonance (²⁹Si NMR) spectroscopy at ambient temperature in a system with BTB:ethanol:water:HCl = 1:10:x:0.8 × 10⁻⁴ (x = 3, 6 or 9). Signals due to hydrolyzed triethoxysilyl groups as well as unhydrolyzed triethoxysilyl groups [−Si(OEt)₃, −Si(OEt)₂(OH), −Si(OEt)(OH)₂ and −Si(OH)₃ (OEt = OCH₂CH₃)] formed four sub-regions based on the number of hydroxyl groups bound to a silicon atom. In addition, one silicon environment influenced the other silicon environment by an intra-molecular interaction between two silicon atoms, and each sub-region for monomeric species thus contained four signals. Based on the development of signal intensity, it is revealed that one of the two triethoxysilyl groups in BTB is hydrolyzed preferentially. Thus, when a triethoxysilyl group is hydrolyzed, the −Si(OH) _x (OEt)_3−x (x = 1, 2) groups formed undergo further hydrolysis, which is opposite to the tendency expected from the hydrolysis behavior of organotrialkoxysilanes under acidic conditions.     

Sandwich-type Uranium-Substituted of Bismuthotungstate: Synthesis and Structure Determination of [Na(UO2)2(H2O)4(BiW9O33)2]13?

The sandwich-type [Na(UO₂)₂(H₂O)₄(BiW₉O₃₃)₂]¹³⁻ uranium (VI) has been synthesized by reacting the trivacant species of B-α-[BiW₉O₃₃]⁹⁻ with and investigated by IR and UV–Vis spectroscopy, and elemental analysis. The X-ray single crystal analysis was carried out on Na₁₃[Na(UO₂)₂(H₂O)₄(BiW₉O₃₃)₂] · 33H₂O (I) which crystallizes in the orthorhombic system, space group Pna2₁ with a = 33.8454(19) ?, b = 21.1484(12) ?, c = 13.2403(7) ?, α = 90°, β = 90°, γ = 90°, and Z = 4. The polyanion consists of two lacunary B-α-[BiW₉O₃₃]⁹⁻ groups which sandwich two uranyl cations and one sodium cation. The uranium atoms adopt distorted pentagonal–bipyramidal coordination, achieved by two equatorial bonds to each BiW₉O₃₃ unit and one external water ligand. The coordination of each uranium atom is evident by the shift of ν_as(W–O_b–W) and ν_as(Bi–O) stretching vibrational bonds. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

The 20-Tungsto-4-Tellurate(IV) [H2Te4W20O80]22− and the 15-Tungstotellurate(IV) [NaTeW15O54]13−

The 20-tungsto-4-tellurate(IV) polyanion [H₂Te₄W₂₀O₈₀]^22? (1) has been synthesized and isolated in the form of its hydrated sodium salt Na₂₂[H₂Te₄W₂₀O₈₀]·64H₂O (Na-1). Na-1 has been characterized in the solid state by FTIR and TGA. Single-crystal X-ray diffraction analysis revealed that Na-1 crystallizes in the triclinic space group P ${\bar 1}The 20-tungsto-4-tellurate(IV) polyanion [H₂Te₄W₂₀O₈₀]²²⁻ (1) has been synthesized and isolated in the form of its hydrated sodium salt Na₂₂[H₂Te₄W₂₀O₈₀]·64H₂O (Na-1). Na-1 has been characterized in the solid state by FTIR and TGA. Single-crystal X-ray diffraction analysis revealed that Na-1 crystallizes in the triclinic space group P , with a = 12.741(2) ?, b = 16.842(3) ?, c = 17.197(4) ?, α = 93.961(10)°, β = 107.466(8)°, γ = 108.548(8)°, V = 3281.5(11) ?³ and Z = 1. The polyanion 1 comprises two [HTe₂W₁₀O₄₀]¹¹⁻ fragments, connected through Te−O–W μ₂-oxo bridges, and each containing a pair of face-shared WO₆ octahedra. Furthermore, the 15-tungstotellurate(IV) polyanion [NaTeW₁₅O₅₄]¹³⁻ (2) was synthesized and crystallized as a sodium salt in the orthorhombic space group Pccn, with a = 11.8841(5) ?, b = 20.8934(11) ?, c = 31.801(2) ?, V = 7896.3(7) ?³ and Z = 4. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Dedicated to Professor C. N. R. Rao on the occasion of his 75th birthday     

Synthesis of chiral α-ethylphenylamine salts of tartaric acid and novel application to cyanosilylation of prochiral ketones

Abstract  

Chiral α-ethylphenylamine tartaric acid salts were synthesized from α-ethylphenylamine by direct reaction with chiral tartaric acid. The crystal structure of S-(−)-α-ethylphenylamine-(2R,3R)-(−)-dihydroxybutanedioic acid was determined. The crystal is monoclinic, of space group P2_1/n , with a = 6.331(5) ?, b = 14.209(11) ?, c = 7.495(6) ?, α = 90.00o, β = 107.000(13)o, γ = 90.00o, λ = 0.7103 Ǻ, V = 644.7(9), Z = 2, D _c = 1.397 g/cm³, M _r  = 271.27 and F(000) = 288, R = 0.0477, and ωR = 0.0838 for 1388 observed reflections with I > 2σ(I). We then used the chiral α-ethylphenylamine tartaric acid salts as catalysts in the cyanosilylation of prochiral ketones, and moderate conversions were obtained.     

Synthesis, structure and spectroscopic characterization of a new organic cation diphosphate: [2,6-(C2H5)2C6H3NH3]2H2P2O7?·?2H2O

The chemical preparation, crystal structure and spectroscopic characterization of [2,6-(C₂H₅)₂C₆H₃NH₃]₂H₂P₂O₇ · 2H₂O have been reported. The compound crystallizes in the monoclinic system in space group P2₁/c and cell parameters a = 14.323(2), b = 11.158(3), c = 16.387(2) ? and β = 96.34(3)°; V = 2602.8(9) ?³ and Z = 4. Crystal structure has been determined and refined to R = 0.044, using 3528 independent reflections. The atomic arrangement of the title compound shows anionic layer of formulae [H₂P₂O₇(H₂O)₂] _n ²ⁿ⁻ stacked along the c-axis. The 2,6-diethylanilinium cations establish on both sides of these inorganic layer hydrogen bonds so as to contribute to the intralayer cohesion in the network. The different building species are held together by means of O–H···O and N–H···O intermolecular hydrogen bonds in addition to electrostatic and van der Waals interactions.     

Two Coordination Modes of Bidentate Aminopyrazine Ligands in Cubane-type Cluster Complex Re4Te4Cl8(C4N3H4)4 · 2DMF

Abstract  A new cubane-type cluster complex Re₄Te₄Cl₄(C₄H₄N₃)₄ · 2DMF has been synthesized by reaction of Re₄Te₄Cl₈(TeCl₂)₄ with 2-aminopyrazine C₄H₅N₃ in DMF. The crystal structure of compound has been solved by X-ray single crystal diffraction method. Crystal data for Re₄Te₄Cl₄(C₄N₃H₄)₄ · 2DMF: a = 22.8718(16) ?, b = 8.5936(7) ?, c = 20.5720(17) ?, β ^o = 106.493(2), V = 3877.1(5) ?³, R ₁ = 0.0466, R _w(F ²) = 0.1191. In the complex bidentate aminopyrazine ligands are coordinated in two different types, namely, two of four aminopyrazine ligands bind to a single rhenium atom, and each of two other ligands is coordinated as bridge between two rhenium atoms. Graphical Abstract  A new cubane-type cluster complex Re₄Te₄Cl₄(C₄H₄N₃)₄  · 2DMF with two coordination modes of bidentate aminopyrazine ligands has been synthesized and structurally characterized.      

Synthesis, crystal and molecular structures of an isomorphic N, S-bridged [Cu2(μ2-I)2(PPh3)2(μ2-N, S-pymSH)] dimer and S-bonded [CuX(η1-S-pymSH)(PPh3)2] monomers (X = Cl, Br)

Abstract  Monoclinic crystals of [Cu₂(μ-I)₂(PPh₃)₂(μ-N, S-pymSH)] · CH₃CN) (1), were obtained by equimolar reaction of copper(I) iodide with pyrimidine-2-thione (pymSH), followed by the addition of triphenylphosphine (PPh₃) in acetonitrile. Crystal data for 1: space group P2₁, Z = 2, a = 9.896, b = 18.378, c = 11.703 ?, β = 101.73°. It has an iodo-bridged Cu(μ-I)₂Cu core and the pyrimdine-2-thione binds to both Cu centers via N, S-bridging across the Cu(μ-I)₂Cu core. This N, S-bridging, a rare coordination mode for pyrimidine-2-thione, leads to a short Cu···Cu separation of 2.675(2) ? (sum of van der Waals radius of Cu atoms, 2.80 ?). The geometry around each Cu center is distorted tetrahedral with angles varying in the range, ca. 102–119°. Copper(I) chloride and bromide also yielded monoclinic crystals of S-bonded tetrahedral monomers, [CuBr(pymSH)(PPh₃)₂] 2 and [CuCl(pymSH)(PPh₃)₂] 3. Crystal data for 2: space group P2₁/n, Z = 8, a = 12.825, b = 43.122, c = 13.396 ?, β = 90.79°. Crystal data for 3: space group P2₁/c, Z = 4, a = 14.340, b = 10.111, c = 24.200 ?, β = 94.36°. Compound 2 has two crystallographically independent molecules in crystal lattice. The ³¹P NMR spectrum of 1 showed two signals for PPh₃ ligands bonded to two Cu centers with different coordination cores: CuI₂PN and CuI₂PS. Both 2 and 3 showed one signal each for PPh₃ in their ³¹P NMR spectra. Graphical abstract  Reaction of copper(I) iodide with pyrimidine-2-thione and triphenylphosphine formed monoclinic crystals of dimer 1 with unusual N, S-bridging across Cu(μ₂-I)₂Cu core.      

Polymorphism and Pressure Driven Thermal Spin Crossover Phenomenon in [Fe( abpt )2(NC X )2] ( X =?S, and Se): Synthesis, Structure and Magnetic Properties

Summary.  The monomeric compounds [Fe(abpt)₂(NCX)₂] (X = S (1), Se (2) and abpt = 4-amino-3,5-bis(pyridin-2-yl)-1,2,4-triazole) have been synthesized and characterized. They crystallize in the monoclinic P2₁/n space group with a = 11.637(2) ?, b = 9.8021(14) ?, c = 12.9838(12) ?, β = 101.126(14)°, and Z = 2 for 1, and a = 11.601(2) ?, b = 9.6666(14) ?, c = 12.883(2) ?, β = 101.449(10)°, and Z = 2 for 2. The unit cell contains a pair mononuclear [Fe(abpt)₂(NCX)₂] units related by a center of symmetry. Each iron atom, located at a molecular inversion center, is in a distorted octahedral environment. Four of the six nitrogen atoms coordinated to the Fe(II) ion belong to the pyridine-N(1) and triazole-N(2) rings of two abpt ligands. The remaining trans positions are occupied by two nitrogen atoms, N(3), belonging to the two pseudo-halide ligands. The magnetic susceptibility measurements at ambient pressure have revealed that they are in the high-spin range in the 2 K–300 K temperature range. The pressure study has revealed that compound 1 remains in high-spin as pressure is increased up to 4.4 kbar, where an incomplete thermal spin crossover appears at around T _1/2 = 65 K. Quenching experiments at 4.4 kbar have shown that the incomplete character of the conversion is a consequence of slow kinetics. Relatively sharp spin transition takes place at T _1/2 = 106, 152 and 179 K, as pressure attains 5.6, 8.6 and 10.5 kbar, respectively. Corresponding author. E-mail: jose.a.real@uv.es Received June 12, 2002; accepted July 1, 2002