Carbon in silica

The structure of paramagnetic centers (PMC) in carbon-doped silica is studied by the EPR and quantum chemistry methods. Three types of radicals, ≡Si-^·CH₂, (≡Si-)₂ ^·CH and (≡Si-)₃C^·, are identified in which the free valence is localized on the impurity carbon atom. Their structure is determined by using samples enriched by isotopes ²D, ²⁹Si, and ¹³C. The assignment of the obtained radiospectroscopic parameters of radicals is confirmed by quantum-chemical calculations of model systems. Based on the obtained data, a conclusion is made that paramagnetic centers (the so-called EX-centers) discovered earlier by the EPR method in silicon oxidation products have the structure (≡Si-)₃C^·, i.e. are not the intrinsic defects of the material but are related to impurity carbon atoms. Differences in the spectral characteristics of the (≡Si-)₃C^· groups observed in experiments are caused by the amorphous structure of silica. The kinetic nonequivalence of the (≡Si-)₃C^· radicals in the reaction of the hydrogen atom detachment from the H₂ molecule is established (the activation energies for different PMC fractions lie in the range from 10 to 17 kcal/mol). The quantum-chemical calculations of model systems performed in the paper suggest that the differences observed in the reactivity of radicals are related to their spatial structure. It is found that the high-temperature pyrolysis of the (≡Si-)₃C-H and (≡Si-O-)₃Si-H groups is accompanied by the quantitative regeneration of free radicals (≡Si-)₃C^· and (≡Si-O-)₃Si^·. The probable mechanism of carbon atom embedding from. (≡Si-O-)₃Si-O-CH₃ groups to silica accompanied by the formation of (≡Si-)₄C groups is analyzed.     

Silver thiolato complexes grafted on silica and dissolved in organic solution

The formation of a covalent, stable, silver-thiolato bond was used to compare the coordination of the silver cation with mercaptopropylsilane molecules grafted on silica and dissolved in organic solvents. The characterization of the homemade ≡SiLH trap, performed by DRIFT, ²⁹Si- and ¹³C-CP-MAS-n.m.r., showed the presence of a ligand monolayer on the silica surface. This ligand was characterized by its free S—H function. The coordination of Ag⁺ ions was illustrated by the color change of the surface from white to yellow, the disappearance of the S—H vibration and the downfield shift of the carbon atoms located near the S atom. All these changes were also observed for the silver thiolates synthesized in homogeneous medium. Three molecular complexes were isolated as yellow solids and characterized using physicochemical techniques. Monomeric [HNEt₃][Ag(NO₃)L²] (1), tetrameric (AgL²)₄ (2) and trimeric (AgL³)₃ (3) species, each with a linearly coordinated silver cation, were proposed. L²H, (MeO)₃Si(CH₂)₃SH, and L³H, N(C₂H₄O)₃Si(CH₂)₃SH, are respectively trimethoxysilyl- and silatranyl- propanethiols. The silver salt and the steric hindrance of the ligand influenced the nuclearity of the molecular silver complexes. Optimization of the ≡SiLH trapping conditions with pH and time indicated that the best trapping of the Ag⁺ cation was performed for pH values 5–7 and 30 min in batch experiments. Safety discharged waters were obtained after percolation through an ≡SiLH filled column. The mercaptopropyl-modified silica gel was regenerated with a 1 M thiourea solution at pH 1.     

Paramagnetic centers by X-ray-irradiation of aluminium hydroxide

EPR spectra of paramagnetic centers originating from X-ray-irradiation of aluminium hydroxide at room temperature have been measured. The EPR spectrum represents a superposition of EPR spectra of ionic centers O^–, holes of type and trapped electrons. Radiation chemical yield of paramagnetic centers observed at room temperature (293 K) is G(spins.)=4.4±0.6) spins per 100 eV absorbed energy. The decay of paramagnetic centers in irradiated Al(OH)₃ was oberved at 293 K. The rate constant of the paramagnetic centers decay in irradiated Al(OH)₃ is K₂=(0.0980±0.0019) kg·mol^–1·min^–1 and their half-life is 9.43±0.18 days.Dedicated to the memory of the late Genrikh Markovis Kolyiari.     

Extrahierte Verbindungen von Gallium, Indium und Thallium in Verteilungssystemen mit Tributylphosphat, Cyclohexanon und Isobutylmethylketon

Zusammenfassung Das Verteilungsverhalten der Halogenide und Halogenometallate von Gallium, Indium und Thallium mit den drei Solventien (S) Tributylphosphat (TBP), Cyclohexanon (Cyclo) und Isobutylmethylketon (IBMK) wurde untersucht. Die extrahierten Verbindungen wurden nach der Geradenmethode nach Asmus, der logarithmischen Methode nach McKay, der Methode der kontinuierlichen Variation, durch Analyse der beiden Phasen und durch konduktometrische Extraktionstitration nachgewiesen. Identifiziert wurden folgende Verbindungen: [GaCl₄]^–·2 S, Ga-(SCN) ₃·3 TBP, [Ga(SCN)₄]^–·2 TBP, [InCl₄]^–·2 TBP, [InBr₄]^–·2TBP, [InBr₄]·x Cyclo, [InBr₄]^–·x IBMK, [InJ₄]^–·2 S, In(SCN)₃·3 TBP, [In(SCN)₄]^–·2 TBP, TlCl₃·1 TBP, [TlCl₄]^–·2 S, TlBr₃·1 TBP, [Tl-Br₄] ^–·2 S, TlJ₃·x TBP und [TlJ₄]^–·xS. Wegen der nicht eindeutig definierten Oxydationsstufe von Thalliumjodiden ergaben sich bei den Versuchen experimentelle Schwierigkeiten. Daher wurde in diesem System zusätzlich das radioaktive Isotop ²⁰⁴Thallium verwendet.

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Extracted compounds of gallium, indium and thallium in distribution systems with tributyl phosphate, cyclohexanone and isobutylmethylketone

The behaviour of distribution of the halides and halogenometallates of gallium, indium and thallium with the three solvents (S) tributylphosphate (TBP), cyclohexanone (Cyclo) and isobutylmethylketone (IBMK) are investigated. The extracted compounds are detected with the straight-line method of Asmus, the logarithmic method of McKay, the method of continuous variation, by analysis of the two phases, and with the conductometric extraction-titration. The following compounds were identified: [GaCl₄]^–·2S, Ga(SCN)₃·3TBP, [Ga(SCN)₄]^–·2TBP, [InCl₄]^–·2TBP, [InBr₄]^–·2TBP, [InBr₄]·x Cyclo, [InBr₄]^–·x IBMK, [InJ₄]^– ·2S, In(SCN)₃·3TBP, [In(SCN)₄]^–·2TBP, TlCl₃·1TBP, [TlCl₄]^–·2S, TlBr₃ ·1TBP, [TlBr₄]^–·2S, TlJ₃·x TBP and [TlJ₄]^–·x S. The not unequivocally defined stage of oxidation of thallium iodides resulted in experimental difficulties. Thus, in this system the radioactive isotope ²⁰⁴thallium was additionally used.

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Herrn Professor Dr. E. Asmus zum 60. Geburtstag gewidmet.

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Wie danken Herrn Priv.-Doz. Dr. H. Nickel für die freundliche Unterstützung bei den in der KFA Jülich durchgeführten radioaktiven Messungen.     

Fragmentation behavior of Si2Cln+ cations (n = 1—6)

Sector-field mass spectrometry was used to probe the fragmentation patterns of the cationic silicon chlorides Si₂Cl_n ⁺ (n = 1—6). For almost all Si₂Cl_n ⁺ ions, Si—Si fragmentation predominates the Si—Cl bond cleavage both in the metastable ion and collisional activation mass spectra. Analysis of the fragmentation patterns indicates that the long-lived radical cation Si₂Cl₆ ^·+ corresponds to a complex [SiCl₂·SiCl₄]^·+ rather than the intact molecular ion of hexachlorodisilane. The behavior of Si₂Cl₅ ⁺ is consistent with the formation of the (trichlorosilyl)dichlorosilyl cation Cl₃SiSICl₂ ⁺. Structural aspects are also discussed for the other Si₂Cl_n ⁺ species. A semi-quantitative analysis of the fragmentation patterns in conjunction with the literature thermochemistry data was used to estimate some thermochemical properties of the Si₂Cl_n ⁺ cations.     

Synthesis and structures of the dinuclear tin(II) complexes [R = Ph, X(Z) = CPh; R = SiMe3, X(Z) = PPh2] and of related compounds

Tin(II) compounds containing the ligands [CH(C₆H₃Me₂-2,5)C(Bu^t)NSiMe₃]⁻ (≡ L¹), [CH(Ph)C(Ph)NSiMe₃]⁻ (≡L²), [CH(SiMe₃)P(Ph)₂NSiMe₃]⁻ (≡ L³),

Full-size image (3K)

(≡ L⁴), [C(Ph)C(Ph)NSiMe₃]²⁻ (≡ L⁵), and [C(SiMe₃)P(Ph)₂NSiMe₃]²⁻ (≡ L⁶) are reported: the transient SnBr(L¹) (1) and SnBr(L²) (2), Sn(L¹)₂ (3) [P.B. Hitchcock, J. Hu, M.F. Lappert, M. Layh, J.R. Severn, J. Chem. Soc., Chem. Commun. (1997) 1189], the labile Sn(L²)₂ (4), [Sn(L⁵)]₂ (5), SnCl(L³) (6), Sn(L³)₂ (7), [Sn(L⁶)]₂ (8), Sn(L⁴)₂ (9) and Pb(L⁴)₂ (10). They were prepared from (i) SnBr₂ and K(L¹) (1, 3) or K(L²) (2, 4, 5); (ii) SnCl₂ and Li(L³) (6–9); or (iii) PbCl₂ and Li(L⁴) (10). Each of 1, 3 and 5–10 has been characterised by multinuclear NMR spectra; 3, 5, 6, 8, 9 and 10 by EI-mass spectra, but only 3, 5, 8, 9 and 10 were isolated pure and furnished X-ray quality crystals. Of greatest novelty are the title binuclear fused tricyclic ladder-like compounds 5 and 8. Quantum chemical calculations, on alternative pathways to 5 from 2 and to 8 from 7, are reported.     

Kinetics of ammoniation of some halobis(ethylenediamine)-rhodium(III) perchlorates in liquid ammonia

Summary The ammoniation ofcis-[Rh(en)₂Cl₂] · (ClO₄) in liquid NH₃ was studied at constant ionic medium of 0.20 m perchlorate in the 0 to 35° range. The complex reacts in two distinct steps to givecis-[Rh(en)₂(NH₃)₂] · (ClO₄)₃, with the intermediate formation ofcis-[Rh(en)₂(NH₃)Cl] · (ClO₄)₂. Both steps follow a conjugate-base mechanism. Activation parameters were obtained for the acid-base preequilibrium and the rate-determining step. The entropies of activation for the rate-determining step are 0 and –42 JK^–1mol^–1 for the first and second ammoniations respectively. These values are considerably lower than those found for the cobalt(III) analogues. The entropy changes for the acid-base equilibria are –84 and –36 JK^–1mol^–1 respectively, which is less negative than those values found for the cobalt(III) analogues. Trans-[Rh(en)₂I₂] · (ClO₄) ammoniates totrans-[Rh(en)₂(NH₃)I] · (ClO₄)₂. The contribution of spontaneous ammoniation to the overall reaction oftrans-[Rh(en)₂I₂] · (ClO₄) is negligible, so the uniqueness oftrans-[Co(en)₂Cl₂] · (ClO₄) among cobalt(III) complexes in this respect is not reproduced for thetrans-dihalotetraamine structure in rhodium(III) complexes. A comparison of cobalt(III) and rhodium(III) amines with respect to activation parameters and the influence of formal charge of the metal complex on reactivity indicates a more associative type of activation for rhodium(III).     

Organosilicon Amine Gels Based on 3-Aminopropyltriethoxysilane, Cobalt(II) or Chromium(III) Clorides, and Triethoxysilane

Organosilicon gels [Co(NH₂R²)₂Cl₂] and [Cr(NH₂R²)₃Cl₃], containing a diaminodichloride complex of cobalt(II) and triaminotrichloride complex of chromium(III) (R² = CH₂CH₂CH₂SiO(OEt)), were synthesized by the hydrolysis of complexes [Co(NH₂R¹)₂Cl₂] (I) and [Cr(NH₂R¹)₃Cl₃] (II) incorporating peripheral triethoxysilyl groups (R¹ = CH₂CH₂CH₂Si(OEt)₃). The coprecipitated [Co(NH₂R²)₂Cl₂] · 4NH₂R³, [Cr(NH₂R²)₃Cl₃] · 6NH₂R³, [Co(NH₂R²)₂Cl₂] · 2SiO₂, and [Cr(NH₂R²)₃Cl₃] ·xSiO₂ · (3 – x)SiHO_1.5 (R³ = CH₂CH₂CH₂SiO_1.5) gels were obtained by cohydrolysis of complexes I and II with 3-aminopropyltriethoxysilane or triethoxysilane. Interaction with SiH(OEt)₃ is accompanied by the decomposition of silicon hydride groups and the formation of tetraethoxysilane derivatives. The heating of dry gels in a flow of argon or oxygen to 600° results in the formation of amorphous silica having a specific surface area 2–467 m²/g and containing crystalline metals, their chlorides, oxides, silicates, or carbides.     

Synthesis and study of binuclear vanadyl complexes with acyldihydrazones of salicylaldehyde and dicarboxylic acids

The binuclear vanadyl(ii) complexes [(VO)₂·2Py·2EtOH]·mH₂O with acyldihydrazones of salicylaldehyde (H₄L) and dicarboxylic acids were synthesized and studied. In these complexes, two chelate vanadyl(ii) complexes with the tridentate bicyclic ligands are linked to each other by the polymethylene bridges —(CH₂) _n — of different lengths varying from one to four units. The ESR spectra of solutions of these complexes, unlike those of analogous copper(ii) complexes, have an isotropic signal with an eight-line hyperfine structure (g = 1.972, a _V = 93·10^–4 cm^–1) typical of monomeric vanadyl complexes, which indicates that no exchange interactions occur between the paramagnetic centers through the polymethylene chain.     

Sulfito- und Thiosulfato-Komplexe des Kobalts(III) mitα-Benzildioxim Überα-Dioximinkomplexe der Übergangsmetalle, 52. Mitt.

Some new ligand exchange reactions of [Co(diph·H)₂Cl(H₂O)] and [Co(diph·H)₂(SO₃)(H₂O)]^– complexes with N₃ ^–, S₂O₃ ^2– and with aromatic and heterocyclic amines were carried out. A series of derivatives of the types [Co(diph·H)₂(SO₃)X] ^n– (X=N₃ ^–, S₂O₃ ^2– oramine) and [Co(diph·H)₂(S₂O₃)₂]^3– were described and characterized. Some structural problems are resolved and discussed on the basis of UV and IR spectral data.     

Chemie der Seltenerdmetalle, 11. Mitt.: Yttriumtartratkomplexe im sauren Bereich

Zusammenfassung Es wurde ein systematisches Studium des Systems im sauren Bereich durchgeführt. Aus den Ergebnissen der pH-Messungen wurden die Gleichgewichtskonstanten der Komplexe [YH₃ T]²⁺, [YH₂ T]⁺, [Y₂H₂ T]⁴⁺, [Y(H₂ T)₂]^– und HYT bestimmt. Es wurden die Verbindungen Y₂(H₂ T)₃ · 8 H₂O, Y₂(H₂ T)₃ · 5 H₂O und H[Y(H₂ T)₂] · 3 H₂O isoliert. Diese wurden mit Hilfe von Röntgenstreuung, Thermoanalyse und IR-Absorptionsspektren untersucht.

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A systematic investigation of the system in the acidic range was undertaken. The equilibrium constants of the complexes [YH₃ T]²⁺, [YH₂ T]^–, [Y₂H₂ T]⁴⁺, [Y(H₂ T)₂]^– and HYT were determined, making use of the results of p_H-measurements. The compounds Y₂(H₂ T)₃ · 8 H₂O, Y₂(H₂ T)₃ · 5 H₂O and H[Y(H₂ T)₂] · 3 H₂O were isolated. Their X-ray diffraction, thermal analysis and IR spectra were investigated.

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Mit 2 Abbildungen

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Zugleich 24. Mitt. der Reihe: Koordinationsverbindungen von organischen Oxoubstanzen; H₄ T=C₄H₆O₆.     

Interaction of Phosphorus Iminoilides with Metal Acetates. Crystal and Molecular Structure of Cu[(2-O–)(5-NO2)C6H3N–CH=CH–+PPh3]2 · 2CHCl3

The structure of the Cu[(2-O^–)(5-NO₂)C₆H₃N–CH=CH–⁺PPh₃]₂ complex with the CuN₂O₂ coordination core of distorted square-planar geometry was established by X-ray diffraction analysis. The molecules in the crystal structure of the Cu[(2-O^–)(5-NO₂)C₆H₃N–CH=CH–⁺PPh₃]₂ · 2CHCl₃ solvate are bound via hydrogen bonds of two types, namely, C(sp ²)–H···O and C(sp ³)–H···O.     

A 2-D bimetallic assembly with bridging cyanide ions

A novel cyanide-bridged bimetallic assembly, [Cu(1,3-Pn)₂]₂[Fe^III(CN)₆]ClO₄ · 2H₂O (1,3-Pn = 1,3-diaminopropane), derived from [Fe(CN)₆]^3– building blocks and four-coordinated bisdiamine metal(II) ions [Cu(1,3-Pn)₂]²⁺ is described and characterized by X-ray crystal analysis. The compound contains a two-dimensional network structure extended through Fe^III—CN—Cu linkages. Mössbauer experimental results indicate that the iron is ferric (Fe³⁺) in the complex. Cryomagnetic measurements reveal an antiferromagnetic exchange interaction between the nearest paramagnetic metal ions in the compound. The exchange mechanism was also discussed.     

Adsorption properties of crystalline silicas: (II) Adsorption of anionic surfactants and delamination

Lamellar crystalline silicas (crystalline silicic acids, chemical composition SiO₂·xH₂O; examples: H₄Si₁₄O₃₀·xH₂O, H₄Si₂₀O₄₂·xH₂O) are distinguished from the amorphous forms by their layered structure and exceptional adsorption properties. One outstanding example is the reaction with anionic surfactants. Several types of crystalline silicas (typical H₄Si₂₀O₄₂·xH₂O) can intercalate ionic pairs consisting of surfactant anion and gegen ion into the interlayer space. The saturation value of SDS adsorption is 0.475 mmol SDS/g H₄Si₂₀O₄₂·3H₂O. The acid H₄Si₁₄O₃₀·xH₂O adsorbs anionic surfactants at the external surfaces only (saturation value 0.04 mmol/g H₄Si₁₄O₃₀·0.8 H₂O). When anionic surfactants are adsorbed in the interlayer space, the layer separation increases to such an extent that the crystals disarticulate in a fan-like manner or delaminate into thinner packets of layers or smaller aggregates. Washing-out the SDS ionic pairs or drying reconstitutes the parallel layer orientation and leads to re-aggregation of the packets and fragments.     

Mn2 Dimers Encapsulated in Silicon Cages: A Complex Challenge to MC-SCF Theory

MC-SCF wavefunctions for three endohedral Mn/Si clusters, Mn₂Si₁₀, Mn₂Si₁₂, and [Mn₂Si₁₃]⁺, show evidence for strong static correlation, both in the Mn-Si bonds (‘in–out correlation’) and between the two Mn centers (‘up–down correlation’). We use both Restricted and Generalized Active Spaces (RAS and GAS) to place constraints on the configurations included in the trial wavefunction, showing that, particularly in the high-symmetry cases, the GAS approach captures more of the static correlation. The important correlating pairs are similar across the series, indicating that the electronic structure of the endohedral Mn₂ unit is, to a first approximation, independent of the size of the silicon cage in which it is embedded.     

Self-assembled macrocyclic molecular squares of Ni(II) derived from carbohydrazones and thiocarbohydrazones: Structural and magnetic studies

Four novel molecular square grids were achieved by self-assembly using the flexible ligands bis(di-2-pyridyl ketone) thiocarbohydrazone (H₂L¹), bis(quinoline-2-carbaldehyde) thiocarbohydrazone (H₂L²), bis(di-2-pyridyl ketone) carbohydrazone (H₂L³) and bis(2-benzoylpyridine) carbohydrazone (H₂L⁴). Three complexes were given a general formula of [Ni(HL)]₄[PF₆]₄ · nH₂O and one [Ni₂(HL²)L²]₂(PF₆)₂ · 7H₂O. The MALDI-MS spectra reveal the formation of tetranuclear molecular squares. The square grid of the Ni(II) centers in all the complexes were organized by deprotonated ligands. The complex [Ni(HL¹)]₄[PF₆]₄ · 11H₂O crystallized as [Ni(HL¹)]₄(PF₆)₄ · 0.5 CH₃CH₂OH · 2.8H₂O and X-ray study revealed octahedral geometries around the Ni(II) centers. Variable temperature magnetic studies suggest intramolecular antiferromagnetic coupling between the Ni(II) electrons by a super exchange mechanism through intervening sulfur/oxygen atoms.     

[H3tren] and [H4tren] fluoride zirconates or tantalates

Four new [H₃tren]³⁺ or [H₄tren]⁴⁺ fluoride zirconates and two new [H₃tren]³⁺ fluoride tantalates are evidenced in the (ZrF₄ or Ta₂O₅)-tren-HF_aq.-ethanol systems at 190 °C: the structurally related phases [H₄tren]·(Zr₂F₁₂)·H₂O and α-[H₄tren]·(Zr₂F₁₂) (P2₁2₁2₁), β-[H₄tren]·(Zr₂F₁₂) (P2₁/c), [H₃tren]₄·(ZrF₈)₃·4H₂O (I23), β-[H₃tren]₂·(Ta₃O₂F₁₆)·(F) (R32) and its monoclinic distortion α-[H₃tren]₂·(Ta₃O₂F₁₆)·(F) (C2/m). α and β-[H₄tren]·(Zr₂F₁₂) and [H₄tren]·(Zr₂F₁₂)·H₂O are built up from (Zr₂F₁₂) dimers of edge sharing ZrF₇ polyhedra while isolated ZrF₈ dodecahedra are found in [H₃tren]₄·(ZrF₈)₃·4H₂O. Linear (Ta₃O₂F₁₆) trimers build α and β-[H₃tren]₂·(Ta₃O₂F₁₆)·(F); they consist of two (TaOF₆) pentagonal bipyramids that are linked to two opposite oxygen atoms of one central (TaO₂F₄) octahedron. A disorder affects the equatorial fluorine atoms of the trimers and eventually carbon or nitrogen atoms of [H₃tren]³⁺ cations.     

Synthesis and X-Ray Crystal Structure of Two Novel Complexes: [M II(phen)3]2V4O12·phen·22H2O(M II=Co, Ni; phen=phenanthroline)

Summary. Two novel compounds, [Co(phen)₃]₂V₄O₁₂·phen·22H₂O (1) and [Ni(phen)₃]₂ V₄O₁₂·phen·22H₂O (2), were prepared from KVO₃–1,10-phenanthroline (phen)–Co(NO₃)₂, resp. NiCl₂–H₂O reaction systems. The compounds 1 and 2 are isomorphous and crystallize in triclinic system, space group P-1. Their crystal structures are formed by two types of layers parallel to 001: a cationic one consisting of [M^II(phen)₃]²⁺ ions and an anionic one containing the cyclic V₄O₁₂ ^4– anions. The solvate phenanthroline and crystal water molecules are located in the cationic and anionic layers, respectively. The IR spectra of 1 and 2 are consistent with the presence of the cyclic V₄O₁₂ ^4– anions in the complexes.Received November 13, 2002; accepted (revised) February 3, 2003 Published online June 2, 2003     

Transition metal complexes with thiosemicarbazide-based ligand – Part LV: Synthesis and X-ray structural study of novel Ni(II) complexes with pyridoxal semicarbazone and pyridoxal thiosemicarbazone

Reaction of aqueous solutions of Ni(NO₃)₂ and pyridoxal semicarbazone (PLSC) in the presence of NaN₃ afforded two complexes, viz. green, paramagnetic binuclear octahedral [Ni₂(PLSC)₂(μ_1,1-N₃)₂(N₃)₂] · 2H₂O (1) and, as admixture, red, octahedral [Ni(PLSC–H)₂] · 2H₂O (2) complex. Under the same reaction conditions, pyridoxal thiosemicarbazone (PLTSC) gave only one diamagnetic square-planar, red complex [Ni(PLTSC–H)N₃] · H₂O (3). In the absence of NaN₃, the reaction of PLTSC and Ni(NO₃)₂ yielded brown paramagnetic octahedral complex [Ni(PLTSC)₂](NO₃)₂ · H₂O (4).     

Thermally induced isomerisation and decomposition of diethylenetriamine complexes of nickel(II) in the solid state

Summary Complexes [NiL₂]X₂·nH₂O (L=diethylenetriamine; n=O when X=CF₃CO₂ or CCl₃CO₂; n=1 when X=Cl or Br, and n=3 when X=0.5SO₄ or 0.5SeO₄) and NiLX₂·nH₂O (n=1 when X=Cl or Br; n=3 when X=0.5SO₄ or 0.5SeO₄) have been synthesised and investigated thermally in the solid state. NiLSO₄ was synthesised pyrolytically in the solid state from [NiL₂]SO₄·[NiL₂]X₂ (X=Cl or Br) undergo exothermic irreversible phase transitions (242–282° C and 207–228° C; H=–11.3 kJ mol^–1 and –1.9 kJ mol^–1 for [NiL₂]Cl₂ and [NiL₂]Br₂, respectively). [NiL₂]-phenomenon (158–185° C; H=2.0 kJ mol^–1). NiLX₂· nH₂O (n=1 or 3) undergo simultaneous deaquation-isomerisation upon heating. All the complexes possess octahedral geometry.