Nitridation of niobium oxide films by rapid thermal processing

The possibility of forming niobium oxynitride through the nitridation of niobium oxide films in molecular nitrogen by rapid thermal processing (RTP) was investigated. Niobium films 200 and 500 nm thick were deposited via sputtering onto Si(100) wafers covered with a thermally grown SiO₂ layer 100 nm thick. These as-deposited films exhibited distinct texture effects. They were processed in two steps using an RTP system. The as-deposited niobium films were first oxidized under an oxygen atmosphere at 450 °C for various periods of time and subsequently nitridated under a nitrogen atmosphere at temperatures ranging from 600 to 1000 °C for 1 min. Investigations of the oxidized films showed that samples where the start of niobium pentoxide formation was detected at the surface and the film bulk still consisted of a substoichiometric NbO_x phase exhibited distinctly lower surface roughness and microcrack densities than samples where complete oxidation of the film to Nb₂O₅ had occurred. The niobium oxide phases formed at the Nb/substrate interface also showed distinct texture. Zones of niobium oxide phases like NbO and NbO₂, which did not exist in the initial oxidized films, were formed during the nitridation. This is attributed to a “snow-plough effect” produced by the diffusion of nitrogen into the film, which pushes the oxygen deeper into the film bulk. These oxide phases, in particular the NbO₂ zone, act as barriers to the in-diffusion of nitrogen and also inhibit the outdiffusion of oxygen from the SiO₂ substrate layer. Nitridation of the partially oxidized niobium films in molecular nitrogen leads to the formation of various niobium oxide and nitride phases, but no indication of niobium oxynitride formation was found. Figure Schematic representation of the phase distribution in 200 nm Nb film on SiO₂/Si substrate after two steps annealing using an RTP system. The plot below represents the SIMS depth profiles of the nitridated sample with the phase assignment     

Nitridation of Niobium Pentoxide Films in Ammonia by Rapid Thermal Processing

The feasibility of niobium oxynitride formation through nitridation of niobium pentoxide films in ammonia by rapid thermal processing (RTP) was investigated. Niobium films 200 and 500 nm thick were deposited by sputtering on Si(100) wafers covered by a 100 nm thick thermally grown SiO₂ layer. These as‐deposited films exhibited distinct texture effects. They were processed in three steps using an RTP system. The as‐deposited niobium films were first nitridated in an ammonia atmosphere at 1000 °C for 1 min and then oxidised in molecular oxygen at temperatures ranging from 400 to 600 °C. Those samples in which a single Nb₂O₅ phase was determined after oxidation were additionally nitridated in ammonia at 1000 °C for 1 min. Investigations show that surface roughness of the samples after oxidation of niobium films first nitridated in ammonia is lower than after direct oxidation of as‐deposited films in oxygen, although the niobium pentoxide phase formed after annealing was the same in both cases. We explain this result as being due to the large expansion of the niobium lattice during the direct oxidation of the niobium film in molecular oxygen and also to the high oxidation rate of the as‐deposited niobium film in oxygen. By incorporation of oxygen in the crystal lattice of niobium and rapid formation of niobium pentoxide, substantial intrinsic stress was built up in the film, frequently resulting in delamination of the film from the substrate. Nitrogen hinders the diffusion of oxygen in nitridated films, which leads to a decrease of the oxidation rate and thus slower formation of Nb₂O₅. Nitridation of the completely oxidised niobium films in ammonia leads to the formation of niobium oxynitride and niobium nitride phases.     

Phase relations in the system V/Nb/O. V. Investigation of mixed crystals V1-xNbxO2

Mixed crystals V_1-xNb_xO₂ exist over the whole area of the quasibinary line VO₂-NbO₂. The existence of Nb_{5+ beside V3+ and V4+ on the V-rich side and V3+ beside Nb5+ and Nb4+ on the Nb-rich side of the mixed crystals is demonstrated by XANES-measurements. The compound VNbO}4_(V0.5_Nb0.5_O2_{) is described as a double oxide with vanadium only as V3+ and niobium only as Nb5+. At this point the electric resistivity of the solid solution shows a maximum.} Received: 11 May 1998 / Revised: 4 August 1998 / Accepted: 10 August 1998     

Structural Variety of Niobium(V) Polyoxo Clusters Obtained from the Reaction with Aromatic Monocarboxylic Acids: Isolation of {Nb2O}, {Nb4O4} and {Nb8O12} Cores

The reactivity of aryl monocarboxylic acids (benzoic, 1- or 2-naphtoic, 4’-methylbiphenyl-4-carboxylic, and anthracene-9-carboxylic acids) as complexing agents for the ethoxide niobium(V) (Nb(OEt)₅ precursor has been investigated. A total of eight coordination complexes were isolated with distinct niobium(V) nuclearities as well as carboxylate complexation states. The use of benzoic acid gives a tetranuclear core Nb₄(μ₂-O)₄(L)₄(OEt)₈] (L=benzoate ( 1 )) with four Nb−(μ₂-O)−Nb linkages in a square plane configuration. A similar tetramer, 7 , was obtained with 2-naphtoic acid by using a 55 % humid atmosphere synthetic route. Two types of dinuclear brick were identified with one central Nb−(μ₂-O)−Nb linkage; they differ in their complexation state, with one bridging carboxylate ([Nb₂(μ₂-O)(μ₂-OEt)(L)(OEt)₆], with L=1-naphtoate ( 3 ) or anthracene-9-carboxylate ( 5 )) or two bridging carboxylate groups ([Nb₂(μ₂-O)(L)₂(OEt)₆], with L=4’-methylbiphenyl-4-carboxylic ( 4 ) or anthracene-9-carboxylate ( 6 )). An octanuclear moiety [Nb₈(μ₂-O)₁₂(L)₈(η₁-L)_4−x(OEt)_4+x] (with L=2-naphtoate, x=0 or 2; 8 ) was obtained by using a solvothermal route in acetonitrile; it has a cubic configuration with niobium centers at each node, linked by 12 μ₂-O groups. The formation of the niobium oxo clusters was characterized by infrared and liquid ¹H NMR spectroscopy in order to analyze the esterification reaction, which induces the release of water molecules that further react through oxolation with niobium atoms, in different {Nb₂O}, {Nb₄O₄} and {Nb₈O₁₂} nuclearities.     

Phase relations in the system V/Nb/O. V. Investigation of mixed crystals V1-xNbxO2

Mixed crystals V_1-xNb_xO₂ exist over the whole area of the quasibinary line VO₂-NbO₂. The existence of Nb_{5+ beside V3+ and V4+ on the V-rich side and V3+ beside Nb5+ and Nb4+ on the Nb-rich side of the mixed crystals is demonstrated by XANES-measurements. The compound VNbO}4_(V0.5_Nb0.5_O2_{) is described as a double oxide with vanadium only as V3+ and niobium only as Nb5+. At this point the electric resistivity of the solid solution shows a maximum.}     

Effect of Brønsted/Lewis Acid Ratio on Conversion of Sugars to 5‐Hydroxymethylfurfural over Mesoporous Nb and Nb‐W Oxides

A series of mesoporous Nb and Nb‐W oxides were employed as highly active solid acid catalysts for the conversion of glucose to 5‐hydroxymethylfurfural (HMF ). The results of solid state ³¹P MAS NMR spectroscopy with adsorbed trimethylphosphine as probe molecule show that the addition of W in niobium oxide increases the number of Brønsted acid sites and decreases the number of Lewis acid sites. The catalytic performance for Nb‐W oxides varied with the ratio of Brønsted to Lewis acid sites and high glucose conversion was observed over Nb₅W₅ and Nb₇W₃ oxides with high ratios of Brønsted to Lewis acid sites. All Nb‐W oxides show a relatively high selectivity of HMF , whereas no HMF forms over sulfuric acid due to its pure Brønsted acidity. The results indicate fast isomerization of glucose to fructose over Lewis acid sites followed by dehydration of fructose to HMF over Brønsted acid sites. Moreover, comparing to the reaction occurred in aqueous media, the 2‐butanol/H₂O system enhances the HMF selectivity and stabilizes the activity of the catalysts which gives the highest HMF selectivity of 52% over Nb₇W₃ oxide. The 2‐butanol/H₂O catalytic system can also be employed in conversion of sucrose, achieving HMF selectivity of 46% over Nb₅W₅ oxide.     

Synthesis of Nb<Subscript>2</Subscript>O<Subscript>5</Subscript>〈B〉 solid precursors and LiNbO<Subscript>3</Subscript>〈B〉 batches and their phase compositions

A process has been developed for preparing boron-doped niobium pentoxides Nb₂O₅〈B〉 to be used as precursors in the sysnthesis of nithium biobate batches LiNbO₃〈B〉 having tailored dopant concentrations. Solutions of various origins were used to isolate Nb₂O₅〈B〉. A method has been advanced to account for boron loss as volatile compounds upon the heat treatment of niobium hydroxide in order to determine the boron amount to be added to niobium hydroxide in the form of H₃BO₃. The boron concentration in LiNbO₃〈B〉 during lithium niobate synthesis is shown to be independent of the origin of the Nb₂O₅〈B〉 precursor with the same as-batch boron concentration. The phase compositions of Nb₂O₅〈B〉 and LiNbO₃〈B〉 have been characterized by X-ray powder diffraction and IR spectroscopy and boron concentrations have been determined for the synthesis of single-phase lithium niobate batches for use in the production of optically uniform single crystals and pore-free piezoelectric ceramics.     

(NH4)3[M2NCl10] (M = Nb,Ta): Synthese,Kristallstruktur und Phasenumwandlung

(NH₄)₃[M₂NCl₁₀] (M = Nb, Ta): Synthesis, Crystal Structure, and Phase Transition The nitrido complexes (NH₄)₃[Nb₂NCl₁₀], and (NH₄)₃[Ta₂NCl₁₀] are obtained in form of moisture-sensitive, tetragonal crystals by the reaction of the corresponding pentachlorides with NH₄Cl at 400 °C in sealed glass ampoules. Both compounds crystallize isotypically in two modifications, a low temperature form with the space group P4/mnc and a high temperature form with space group I4/mmm. In case of (NH₄)₃[Ta₂NCl₁₀] a continuous phase transition occurs between –70 °C and +60 °C. For the niobium compound this phase transition is not yet fully completed at 90 °C. The structure of (NH₄)₃[Nb₂NCl₁₀] was determined at several temperatures between –65 °C und +90 °C to carefully follow the continuous phase transition. For (NH₄)₃[Ta₂NCl₁₀] the structure of the low temperature form was determined at –70 °C, and of the high temperature form at +60 °C. The closely related crystal structures of the two modifications contain NH₄⁺ cations and [M₂NCl₁₀]^3– anions. The anions with the symmetry D_4h are characterized by a symmetrical nitrido bridge M=N=M with distances Nb–N = 184.5(1) pm at –65 °C or 183.8(2) pm at 90 °C, and Ta–N = 184.86(5) pm at –70 °C or 184.57(5) pm at 60 °C.     

Effects of Nb substitution on structure and electrochemical properties of LiNi<Subscript>0.7</Subscript>Mn<Subscript>0.3</Subscript>O<Subscript>2</Subscript> cathode materials

Nb-doped cathode materials with the formula Li(Ni_0.7Mn_0.3)_1?xNb_xO₂ (x?=?0, 0.01, 0.02, 0.03, 0.04) have been prepared successfully by calcining the mixtures of LiOH·H₂O, Nb₂O₅, and Ni_0.7Mn_0.3(OH)₂ precursor formed through a simple continuous co-precipitation method. The effects of Nb substitution on the crystal structure and electrochemical properties of LiNi_0.7Mn_0.3O₂ were studied systematically by X-ray diffraction (XRD), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), and various electrochemical measurements. The results show that the lattice parameters of the Nb substitution LiNi_0.7Mn_0.3O₂ samples are slightly larger than that of pure LiNi_0.7Mn_0.3O₂, and the basic α-NaFeO₂ layered structure does not change with the Nb doping. What’s more, better morphology, lower resistance, and good cycle stability were obtained after Nb substitution. In addition, CV test exhibits that Nb doping results in lower electrode polarization and XPS results indicate that the valence of Mn kept constant but the component of Ni³⁺ decreased after doping. All the results indicate that Nb doping in LiNi_0.7Mn_0.3O₂ is a promising method to improve the properties of Ni-rich lithium-ion batteries positive-electrode materials.     

Niobium isocyanide complexes,Nb(CNAr)6, with Ar = 2,6‐dimethylphenyl (Xyl), a diamagnetic dimer containing four reductively coupled isocyanides,and Ar = 2,6‐diisopropylphenyl (Dipp), a paramagnetic monomer analogous to the highly unstable hexacarbonylniobium(0)

Treatment of bis(mesitylene)niobium(0) with 6–7 equivalents of 2,6‐dimethylphenyl isocyanide (CNXyl) affords two products with the empirical formula Nb(CNXyl)_n (n = 7 or 6), which have been shown to be the diamagnetic dimers bis[μ‐N,N′,N′′,N′′′‐tetrakis(2,6‐dimethylphenyl)squaramidinato(2?)]bis[pentakis(2,6‐dimethylphenyl isocyanide)niobium(I)], [Nb₂(C₉H₉N)₁₀(C₃₆H₃₆N₄)] or [Nb(CNXyl)₅]₂[μ‐C₄(NXyl)₄]·xSolvent, 1 , and bis[μ‐N,N′,N′′,N′′′‐tetrakis(2,6‐dimethylphenyl)squaramidinato(2?)]bis[tetrakis(2,6‐dimethylphenyl isocyanide)niobium(I)] tetrahydrofuran trisolvate, [Nb₂(C₉H₉N)₈(C₃₆H₃₆N₄)]·3C₄H₈O or [Nb(CNXyl)₄]₂[μ‐C₄(NXyl)₄]·3THF (THF = tetrahydrofuran), 2 . Each contains Nb^I bound to either five or four terminal isocyanides, respectively, and to an unprecedented bridging tetraarylsquaramidinate(2?) unit, coordinated as a bidentate ligand to each niobium center, symmetrically due to the crystallographic inversion center that coincides with the centroid of the central C₄ unit. Thus, in the presence of CNXyl, the bis(mesitylene)niobium(0) is oxidized to niobium(I), resulting in the facile loss of both mesitylene groups and the reductive coupling of two CNXyl groups per niobium to provide the first examples of tetraarylsquaramidinate(2?) ligands, [cyclo‐C₄N₄Ar₄]^2?, coordinated to metals. In contrast, bis(mesitylene)niobium(0) reacts with the more crowded 2,6‐diisopropylphenyl isocyanide (CNDipp) to afford the paramagnetic monomer hexakis(2,6‐diisopropylphenyl isocyanide)niobium(0), [Nb(C₁₃H₁₇N)₆] or Nb(CNDipp)₆, 3 , the first zero‐valent niobium isocyanide analog of the highly unstable Nb(CO)₆, which is presently only known to exist in an argon matrix at 4.2 K.     

Kinetic Analysis of Calorimetric Measurements of Niobium–Aluminum Nb/Al Multifilament Strands

The formation of different phases for the reaction of Nb and Al in M/s Hitachi Ltd made wires using differential scanning calorimetry (DSC) has been investigated. The interfacial diffusion reaction has been studied in the temperature range 100–990 °C. Niobium (Nb) and aluminum (Al) react to form the phase NbAl₃, subsequently NbAl₃ reacts with the remaining Nb to form the A15 phase. The interfacial reactions play an important role. At higher heating rates, NbAl₃ and bcc‐structured NbAl are formed prior to the formation of Nb₃Al, but at lower heating rates the phase observed indicates σ phase Nb₂Al. DSC has been performed at different heating rates under nonisothermal conditions aimed to measure activation energy of crystallization for different phases: employing Kissinger's equation, Matusita–Sakka theory, and the Augis‐Bennett method. Activation values calculated from these three different methods are found to be in good agreement with each other. The activation energy for the first phase (NbAl₃) is lower than the other two phases (Nb₃Al) A15 phase and Nb₂Al, suggesting that NbAl₃ formation occurs easily. The value of n relating to the nucleation and growth mechanisms has also been calculated using the modified Kissinger method at different temperatures.     

Electrochemical formation of anodic oxide films on Nb surfaces: ellipsometric and Raman spectroscopical studies

Electrochemical formation of anodic oxide films on niobium (Nb) surfaces in 1 M H₂SO₄ solutions was studied using ellipsometry and Raman spectroscopy. By in situ ellipsometric measurements, the coefficient of film thickness growth and the complex index of refraction of anodic oxide films in the voltage range between 0 and 100 V were determined. The Raman spectra reveal that the thin passive films are amorphous. In the beginning of crystallization, the anodic oxide films consist of mixtures of NbO₂ and Nb₂O₅, while NbO₂ is completely transformed to Nb₂O₅ for thicker and well-crystallized films.     

Das neue ternäre Borid Mg8Pt4B und die neue intermetallische Verbindung PtMg2

The New Ternary Boride Mg₈Pt₄B and the New Intermetallic Compound PtMg₂ The new magnesium platinum boride Mg₈Pt₄B was obtained from a reaction of the elements in sealed niobium tubes. It crystallizes isotypically with Mg₈Rh₄B in the cubic space group with a =12.2481(1) Å and can be structurally derived from the Ti₂Ni structure type, where boron occupies cavities, which are formed by four magnesium and four platium atoms. The new intermetallic compound PtMg₂ was also prepared by reaction of the elements in a sealed Nb container and adopts the tetragonal CuAl₂ type structure, space group I4/mcm with a = 6.334(1) Å and c = 5.621(1) Å.     

Zur Präparation und Struktur gemischtvalenter Niob-Wolframoxide der Zusammensetzung (Nb,W)17O47

Preparation and Structure of Niobium Tungsten Oxides (Nb,W)₁₇O₄₇ with Mixed Valency The formal substitution of 2Nb⁵⁺ by Nb⁴⁺ or W⁴⁺, respectively, and W⁶⁺ leads to tungsten niobium oxides (Nb,W)₁₇O₄₇ with mixed valency. The phases Nb_8-nW_9+nO₄₇ with n = 1 to 5 could be obtained by heating (1 250°) mixtures of NbO₂ or WO₂, respectively, with Nb₂O₅ and WO₃. The products crystallize with the structure of Nb₈W₉O₄₇. This is proved by X-ray powder diffraction and transmission electron microscopy. A further decrease of the Nb-content results in two-phase products.     

Na3Al2Nb34O64 und Na (Si,Nb) Nb10O19: Clusterverbindungen mit isolierten Nb6-Oktaedern

Na₃Al₂Nb₃₄O₆₄ and Na (Si, Nb) Nb₁₀O₁₉. Cluster Compounds with Isolated Nb₆-Octahedra Hexagonal ormolu coloured plates of the new compounds Na₃Al₂Nb₃₄O₆₄ ( I ) and Na(Si, Nb)Nb₁₀O₁₉ ( II ) were prepared by heating pellets of NaF, Al₂O₃, NbO₂ and NbO (3:1:8:2) and NaF, NbO₂ and NbO (1:4:2), respectively, at approx. 850°C. I was contained in a sealed gold capsule, II in a silica tube. The Si incorporated in II originates from the container material. Both compounds crystallize in R 3 , I with a = 784.4(1), c = 7065(1) pm, Z = 3 and II with a = 784.1(1), c = 4221.8(5) pm, Z = 6. I and II represent new structure types. They contain the same characteristic structural units, namely discrete Nb₆O₁₂ clusters (d_Nb–Nb = 283 ± 4 pm) and Nb₂O₁₀ units with Nb–Nb dumbells (d_Nb–Nb ≈? 269 pm) in edgesharing coordination octahedra. In addition NbO₆ octahedra containing Nb in the oxidation state + 5 and NaO₁₂ cube-octahedra occur in both compounds besides AlO₄ and SiO₄ tetrahedra in I and II , respectively. The structures can be described in terms of a common closepacking of O and Na atoms together with Nb₆ octahedra.     

[{Cp2(tBuSe)Nb}2E] (E = O and Se) with bridging oxide or selenide ligands

The title compounds, μ‐oxido‐bis[(tert‐butylselenolato)bis(η⁵‐cyclopentadienyl)niobium(IV)] toluene solvate, [Nb₂(C₅H₅)₄(C₄H₉Se)₂O]·C₇H₈, and μ‐selenido‐bis[(tert‐butylselenolato)bis(η⁵‐cyclopentadienyl)niobium(IV)], [Nb₂(C₅H₅)₄(C₄H₉Se)₂Se], consist of niobium(IV) centres each bonded to two η⁵‐coordinated cyclopentadienyl groups and one tert‐butylselenolate ligand and are the first organometallic niobium selenolates to be structurally characterized. A bridging oxide or selenide completes the niobium coordination spheres of the discrete dinuclear molecules. In the oxide, the O atom lies on an inversion centre, resulting in a linear Nb—O—Nb linkage, whereas the selenide has a bent bridging group [Nb—Se—Nb = 139.76 (2)°]. The difference is attributable to strong π bonding in the oxide case, although the effects on the Nb—C and Nb—Se^tBu bond lengths are small.     

One-pot synthesis of Nb-modified Al<Subscript>2</Subscript>O<Subscript>3</Subscript> support for NiMo hydrodesulfurization catalysts

The effect of Nb as a support modifier on the NiMo₆/Al₂O₃–Nb₂O₅(x) (x?=?0, 1, 4, and 8?wt% Nb) catalysts was studied. The supports were prepared by one-pot coprecipitation from soluble precursors. The XRF analysis of the catalysts showed that the contents of Mo and Ni increased slightly with the presence of Nb. Micropore area and pore volume augmented importantly with Nb content, resulting in pore diameters between 5.3 and 9.3?nm. XPS analysis showed that the presence of Nb decreases the active metal–support interaction, improving the Mo and Ni sulfidation degree. The Raman spectra of sulfided catalysts suggested an increase in the number of layers of MoS₂ in the presence of Nb. Generally, the thiophene HDS activity at normal pressure of sulfided NiMo₆/Al₂O₃–Nb₂O₅(8) was greater than that of the sulfided catalysts with x?=?0, 1, and 4?wt% Nb, which can be attributed to the Nb promotion that would have an effect on the type of active site (Brønsted or Lewis acidic sites), since the number of sites by CO chemisorption for sulfided NiMo₆/Al₂O₃–Nb₂O₅(x) did not show correlation with the catalytic activity. The high-pressure HDS activity of dibenzothiophene was also greater in the presence of Nb, and the hydrogenation route was preferred for the Nb-promoted solid, while the unpromoted one showed a larger yield of direct desulfurization products.

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Unexpected Synergy between Magnetic Iron Chains and Stacked B6 Rings in Nb6Fe1−xIr6+xB8

The synergistic combination of experiment and density functional theory has led to the discovery of the first ferromagnetic material, Nb₆Fe_1?xIr_6+xB₈, containing in its crystal structure iron chains embedded in stacked B₆ rings. The strong ferromagnetic Fe–Fe interactions found in the iron chains induce an unexpected strengthening of the B–B interactions in the B₆ rings. Beside these strong B–B interactions, strong interlayer metal–boron bonds (Ir–B and Nb–B) ensure the overall structural stability of this phase, while the magnetic Fe–Fe interactions are mainly responsible for the observed ferromagnetic ordering below T_C=350 K.     

A6Nb4S22 (A = Rb and Cs), compounds with the tetrameric complex anion [Nb4S22]6−: Preparation via the molten flux method and crystal structure determination

The new ternary niobium polysulfides A₆Nb₄S₂₂ were prepared at a low temperature of 350°C via the molten flux method by reacting A₂S₃ (A = Rb, Cs) with niobium metal and additional sulfur. The crystal structure is characterized by [Nb₄S₂₂]^6? anions. Two Nb₂S₁₀ subunits are joined by a S₂^2?. Nb⁵⁺ is coordinated by S₂^2? and S^2? ligands according to [Nb₂(μ-η², η¹-S₂)(η²-S₂)₃(S)₂]₂(μ-η¹-S₂)^6?. Every Nb is in a sixfold coordination, and the polyhedra can be regarded as strongly distorted pentagonal pyramids. Within the unit cell the anions are stacked in “rods” parallel to the crystallographic b-axis. These stacks are arranged in “layers” and the A⁺ ions are located between the layers.     

Thiocyanate Compounds of [Nb6Cl12]2+: The structure of A4[Nb6Cl12(NCS)6](H2O)4 (A = K,Rb, NH4)

New compounds of the general formula A₄[Nb₆Cl₁₂(NCS)₆](H₂O)₄ (A = K, Rb, NH₄) were synthesized from Nb₆Cl₁₄ and ASCN in aqueous solutions. X-ray structure refinements were performed on single-crystal data of the three compounds. They are isotypic and crystallize with the space group P1 (Z = 1) and the lattice parameters: a = 877.9(3) pm, b = 1176.6(3) pm, c = 1187.0(3) pm, α = 114.29(1)°, β = 98.96(2)°, γ = 100.91(2)° for K₄[Nb₆Cl₁₂(NCS)₆](H₂O)₄ ( 1 ); a = 887.6(3) pm, b = 1184.0(4) pm, c = 1195.4(4) pm, α = 114.95(2)°, β = 98.84(2)°, γ = 101.31(2)° for Rb₄[Nb₆Cl₁₂(NCS)₆](H₂O)₄ ( 2 ) and a = 886.0(4) pm, b = 1181.1(6) pm, c = 1183.9(6) pm, α = 114.49(2)°, β = 99.48(3)°, γ = 101.53(1)° for (NH₄)₄[Nb₆Cl₁₂(NCS)₆](H₂O)₄ ( 3 ). Each centrosymmetric [Nb₆Cl₁₂(NCS)₆]^4? ion of the isotypic compounds contains six terminal thiocyanate groups being bound to the corners of the octahedral niobium cluster through the nitrogen atoms (d_{Nb? N} = 221.5(6)–224.3(6) pm, bond angles Nb? N? C 168.6(5)–176.4(6)°). The [Nb₆Cl₁₂(NCS)₆]^4? ions are linked via A? S and A? Cl interactions with the A cations. Half of the cations occur to be disordered along two crystallographic sites.