Sulfur resistance and stability of yttrium-stabilized binary Co-Cu and Ni-Cu composites with zirconium dioxide in the oxidative conversion of methane

Binary Co-Cu and Ni-Cu composites with YSZ have demonstrated rather high thermal resistance (up to 1000 °C) and stability in the extensive oxidation of methane. The tendency of the nickel–copper composites to carbon deposition depends on the amount of nickel introduced. The higher stability was found for the sample with active phase containing 4% Ni, 16% Cu. The sulfur resistance of the palladium-doped Ni–Cu composite is attributed to the formation of an adsorbed [PdO·SO₂] complex. TPHR data indicated that the oxygen in this sample is less reactive in methane oxidation.     

Jahn-Teller-Verzerrungen von Übergangsmetallionen in tetraedrischer Koordination – die Strukturen von Cat[MII(NCS)4] (MII: Co,Ni, Cu) und von Spinellmischkristallen MIICr2O4(MII: Zn?Ni,Zn?Cu,Cu?Ni)

Jahn-Teller Distortions of Transition Metal Ions in Tetrahedral Coordination — The Structures of Cat[M^II(NCS)₄]^II (M^II: Co, Ni, Cu) and of Mixed Crystals M^IICr₂O₄(M^II: Zn? Ni, Zn? Cu, Cu? Ni) of the Spinel Type The structure determination of compounds Cat[M^II(NCS)₄] with Cat = p-xylylenebis(triphenylphosphonium)²⁺ and M^II = Co, Ni, Cu [space group P2₁/n, Z = 4] yielded pseudotetrahedral M^IIN₄-polyhedra, which are distorted by packing forces and vibronic coupling effects of the Jahn-Teller type. Spinel mixed crystals with M^II = Zn? Ni, Zn? Cu, Ni? Cu in the tetrahedral sites exhibit phase transition to tetragonal and o-rhombic structures, induced by cooperative Jahn-Teller interactions. The distortion symmetries of the M^IIN₄ and M^IIO₄ tetrahedra are analysed on the basis of the respective electronic groundstate and the possible Jahn-Teller active vibrational modes.     

The use of hydrogenated Schiff base ligands in the synthesis of multi-metallic compounds II

Tris(2-hydroxybenzylaminoethyl)amine (H₃L) complexes of nickel, copper and zinc are investigated as potential metallo-ligands ([(H_xL)M]; x = 0, 1: M = Ni, Cu, Zn). The homometallic complexes formed are dimetallic ([{(HL)Ni}Ni(OAc)₂] and [{(L)Zn}ZnCl]), tetrametallic ([{(L)Cu}Cu]₂²⁺) and hexametallic ([{(L)Ni}Ni₂(μ-OH)₂(OEt)(OH₂)]₂). Hetero-dimetallic complexes can be formed with [(HL)Ni] and copper chloride ([{(HL)Ni}CuCl₂]) or zinc bromide ([{(HL)Ni}ZnBr₂]). The metallo-ligand acts as a chelating agent using phenolate pairs. The remaining phenolate either does not coordinate or can be used to increase the number of metals included in the scaffold from two to four or six. Not all combinations are possible and [(HL)Cu]⁺ produces a charge separated species with zinc chloride rather than a complex. An exchange reaction is observed to take place when [(HL)Zn]⁺ is treated with the halides of nickel or copper producing [(HL)M]⁺ (M = Ni, Cu, respectively).     

Modifizierung von Schichtsilicaten mit sterisch anspruchsvollen Metallkomplexen. 3. Synthese und Intercalation der planar-quadratischen Komplexe [Cu(bppep)(H2O)](ClO4)2 und [Ni(bppep)(Cl)Cl] (bppep = 2,6-Bis[1-phenyl-1-(pyridin-2-yl)ethyl]pyridin) in Hectorit

Modification of Layer Silicates by Sterically Demanding Metal Complexes: Synthesis and Intercalation of the Square Planar Complexes [Cu(bppep)(H₂O)](ClO₄)₂ and [Ni(bppep)(Cl)]Cl (bppep = 2,6-Bis[1-phenyl-1-(pyridine-2-yl)ethyl]pyridine) in Hectorite Sodium-aqua hectorite reacts with [Cu(bppep)(H₂O)](ClO₄)₂ and [Ni(bppep)(Cl)]Cl with exchange of the sodium-aqua cations against the complex cations [Cu(bppep)(H₂O)]²⁺ and [Ni(bppep)(Cl)]⁺, respectively. In addition, cation-anion pairs of [Cu(bppep)(H₂O)](ClO₄)₂ and [Ni(bppep)(Cl)]Cl are also intercalated between the hectorite layers (intersalation). On the other hand, it is possible to synthesize [Cu(bppep)(H₂O)]²⁺ or [Ni(bppep)(H₂O)]²⁺ modified hectorites without additional ion-pair intercalation (intersalation) by reaction of nickel- and copper-hectorites with the bppep ligand.     

Electrochemical Behaviour of HOPG and CVD‐Grown Graphene Electrodes Modified with Thick Anthraquinone Films by Diazonium Reduction

Highly oriented pyrolytic graphite (HOPG) and graphene grown on Ni (Ni‐Gra) or Cu (Cu‐Gra) by chemical vapour deposition were modified with thick anthraquinone (AQ) films (7?60 nm) by redox grafting of the pertinent diazonium salt. Glassy carbon (GC) electrodes were used for comparison. The AQ‐modified GC electrodes showed excellent blocking properties towards the Fe(CN)₆^3?/4? redox probe, although it was noted that in the case of Ni‐Gra and Cu‐Gra, the blocking ability depended strongly on the underlying substrate. Oxygen reduction studies revealed good electrocatalytic activity of AQ‐modified HOPG, Ni‐Gra, and Cu‐Gra, compared with the bare electrodes.     

Vergleichende atomabsorptionsspektrometrische untersuchungen zur elementspurenbestimmung in Urin

When using a direct determination procedure with graphite-furnace a.a.s. (e.t.a.a.s.), it is sufficient to make an addition of nitric acid in order to arrive at the optimal reduction of the spectral background. A “matrix modifier” (NH₄NO₃, (NH₄)₂HPO₄) produces a background which often cannot be compensated completely. Detection limits of the direct determination technique are: Cd 0.1, Co 8, Cu 4, Ni 5, Pb 2 and Tl 3 (μg l^?1). A similar power of detection can be achieved as with flame-a.a.s. due to a preceding preconcentration step (trace adsorption on highly dispersed silicic acid). After preconcentration and determination with e.t.a.a.s., the detection limits are: Cd 0.002, Co 0.1, Cu 0.05, Ni 0.09, Pb 0.09 and Tl 0.06 (μg l^?1). The trace concentrations in urine of healthy persons were found to be: Cd 0.2–0.8, Co ? 0.1, Cu 4–10, Ni 1–3, Pb 6–10 and Tl 0.7–1.3 (μg l^?1). Direct e.t.-a.a.s. is, therefore, found to be suitable for the determination of Cd, Cu and Pb. For the determination of Co, Ni and Tl concentrations, a preconcentration is required. Cobalt was not found in any of the urine samples at the limit of detection of 0.1 μg l^?1.     

1-Bis(carboxymethyl)amino-butandion-2,3-dioxim als ambifunktioneller Ligand in Komplexen der 3d-Elemente

1-Bis(carboxymethyl)amino-butanedione-2,3-dioxime as an Ambifunctional Ligand in Complexes of 3d Elements In acid solution 1-bis(carboxymethyl)amino-butanedione-2,3-dioxime H₄A affords octahedral 1,1 complexes M^II(H₂A)(H₂O)_x (M^II = Cu, Ni, Co) coordinating as a tetradentate ligand by the imino diacetic acid group and the oxime group in 2-position. At 4.5 < pH < 8 Ni(H₂A)(H₂O)_x and Cu(H₂A)(H₂O)_x are deprotonated, in addition to Ni(HA)^? the binuclear chelate [Ni₂(HA)₂]^2? is formed. In solution containing a surplus of ligand H₄A also the planar chelate [Ni(HA)₂]^4? with the donor set N₄ can be detected. The transition from [Ni(HA)]^? to [Ni(HA)₂]^4? is connected with a change of the coordination sphere (imino diacetic acid group → dioxime group) and the cis-trans isomerization of at least one oxime group. Protonation and stability constants are given and the properties of solid complexes are described.     

Post-Nickelation of a Crystalline Trinuclear Copper Organic Framework for Synergistic Photocatalytic Carbon Dioxide Conversion

Rational regulation of electronic structures and functionalities of framework materials still remains challenging. Herein, reaction of 4,4′,4′′-nitrilo-tribenzhydrazide with tris(μ₂-4-carboxaldehyde-pyrazolato-N,N′)-tricopper (Cu₃Py₃) generates the crystalline copper organic framework USTB-11(Cu). Post-modification with divalent nickel ions affords the heterometallic framework USTB-11(Cu,Ni). Powder X-ray diffraction and theoretical simulations reveal their two-dimensional hexagonal structure geometry. A series of advanced spectroscopic techniques disclose the mixed Cu^I/Cu^II state nature of Cu₃Py₃ in USTB-11(Cu,Ni) with a uniform bistable Cu₃⁴⁺(Cu^I₂Cu^II) : Cu₃⁵⁺(Cu^ICu^II₂) (ca. 1 : 3) oxidation state, resulting in a significantly improved formation efficiency of the charge-separation state. This endows the Ni sites with enhanced activity and USTB-11(Cu,Ni) with outstanding photocatalytic CO₂ to CO performance with a conversion rate of 22 130 μmol g⁻¹ h⁻¹ and selectivity of 98 %.     

Microstructure of metallic copper nanoparticles/metallic disc interface in metal–metal bonding using them

This paper describes a metal–metal bonding technique using metallic Cu nanoparticles prepared in aqueous solution. A colloid solution of metallic Cu particles with a size of 54 ± 15 nm was prepared by reducing Cu²⁺ (0.01 M (CH₃COO)₂Cu) with hydrazine (0.6 M) in the presence of stabilizers (5 × 10^?4 M citric acid and 5 × 10^?3 M cetyltrimethylammonium bromide) in water at room temperature in air. Discs made of metallic materials (Cu, Ni/Cu, or Ag/Ni/Cu) were successfully bonded under annealing at 400 °C and pressurizing at 1.2 MPa for 5 min in H₂ gas with help of the metallic Cu particle powder. Shear strength required for separating the bonded discs was 27.9 ± 3.9 for Cu discs, 28.1 ± 4.1 for Ni/Cu discs, and 13.8 ± 2.6 MPa for Ag/Ni/Cu discs. Epitaxial crystal growth promotes on the discs with a good matching for the lattice constants between metallic nanoparticles and metallic disc surfaces, which leads to strong bonding. Copyright © 2013 John Wiley & Sons, Ltd.     

Metal‐Organic Niccolite: Synthesis,Structures, Phase Transition,and Magnetic Properties of [CH3NH2(CH2)2NH2CH3][M2(HCOO)6] (M=divalent Mn,Fe, Co,Ni, Cu and Zn)

We report the synthesis, crystal structures, thermal and magnetic characterizations of a family of metal‐organic frameworks adopting the niccolite (NiAs) structure, [dmenH₂²⁺][M₂(HCOO)₆²⁻] (dmen=N,N′‐dimethylethylenediamine; M=divalent Mn, 1Mn ; Fe, 2Fe ; Co, 3Co ; Ni, 4Ni ; Cu, 5Cu ; and Zn, 6Zn ). The compounds could be synthesized by either a diffusion method or directly mixing reactants in methanol or methanol–water mixed solvents. The five members, 1Mn , 2Fe , 3Co , 4Ni , and 6Zn are isostructural and crystallize in the trigonal space group P 1c, while 5Cu crystallizes in C2/c. In the structures, the octahedrally coordinated metal ions are connected by anti–anti formate bridges, thus forming the anionic NiAs‐type frameworks of [M₂(HCOO)₆²⁻], with dmenH₂²⁺ located in the cavities of the frameworks. Owing to the Jahn–Teller effect of the Cu²⁺ ion, the 3D framework of 5Cu consists of zigzag Cu‐formate chains with Cu OCHO Cu connections through short basal Cu O bonds, further linked by the long axial Cu O bonds. 6Zn exhibits a phase transition probably as a result of the order–disorder transition of the dmenH₂²⁺ cation around 300 K, confirmed by differential scanning calorimetry and single crystal X‐ray diffraction patterns under different temperatures. Magnetic investigation reveals that the four magnetic members, 1Mn , 2Fe , 3Co , and 4Ni , display spin‐canted antiferromagnetism, with a Néel temperature of 8.6 K, 19.8 K, 16.4 K, and 33.7 K, respectively. The Mn, Fe, and Ni members show spin‐flop transitions below 50 kOe. 2Fe possesses a large hysteresis loop with a large coercive field of 10.8 kOe. The Cu member, 5Cu , shows overall antiferromagnetism (both inter‐ and intra‐chains) with low‐dimensional characteristics.     

Extraction of heterometal ruthenium(II) complexes by diphenyl(dibutylcarbamoylmethyl)phosphine oxide from nitrate-nitrite solutions

The synergistic extraction of [RuNO(NO₂)₄OH]^2? by diphenyl(dibutylcarbamoylmethyl)phosphine oxide (L) in the presence of nonprecious metal cations (M²⁺) is studied; the extraction occurs on the account of the formation of heterometal complexes [RuNO(NO₂)₄OHML_m] (M = Zn, Cu, Co, Ni) due to the addition of M²⁺ to ruthenium through the oxygen atoms of the OH and NO₂ groups and the bidentate coordination of L to M²⁺. The extraction constants for Ru/M complexes and ML_n(NO₃)₂ are determined. The variation in the extraction constants with changing M (Co, Zn, Cu > Ni) does not agree with the Irwing-Williams row, unlike the extraction with monodentate PO-containing extractants (Zn > Cu > Co > Ni). The feasibility of ruthenium extraction in the form of Ru/M complexes from complex nitrate-nitrite solutions is demonstrated.     

First homo- and hetero-nuclear complexes of a chemical messenger-histamine: Cu(II) complex being a supramolecular assembly based on hydrogen bond, Ni(II)?π and C-H?π non-covalent interactions

In this study, the first homo- and hetero-nuclear cyanocomplexes of histamine (His), namely, [Cu(His)₂][Ni(CN)₄], [Ni(His)₂Ni(CN)₄]_n and [Cd(His)Ni(CN)₄]_n are investigated by X-ray diffraction (XRD) technique, electron paramagnetic resonance (EPR) and infrared (IR) spectroscopy. Besides being the first hetero-nuclear complex of histamine, [Cu(His)₂][Ni(CN)₄] complex has an interesting property as being a supramolecular structure constructed by three different non-covalent interactions as hydrogen bond, Ni(II)?π and C-H?π interactions. In [Cu(His)₂][Ni(CN)₄] complex histamine exists in gauche conformation and N^τ-H tautomeric form, and plays an important role in supramolecular structure formation by participating in non-covalent interactions through its aminoethyl side chain and imidazole group. The shifts and splittings in the stretching vibrations of cyano groups show that [Ni(His)₂Ni(CN)₄]_n and [Cd(His)Ni(CN)₄]_n complexes are one-dimensional and three-dimensional coordination polymers, respectively. In [Ni(His)₂Ni(CN)₄]_n complex, histamine acts as a chelating ligand by adopting gauche conformation. In [Cd(His)Ni(CN)₄]_n complex, Cd(II) ions and [Ni(CN)₄]²⁻ anions form two-dimensional layered structure and histamine has a novel bonding mode as a bridging ligand between these layered structures. It is concluded that histamine may have trans conformation and Nπ-H tautomer as a bridging ligand in [Cd(His)Ni(CN)₄]_n complex, which has not been reported so far for the solid structures of bidentate histamine. EPR studies on [Cu(His)₂][Ni(CN)₄] and Cu²⁺-doped [Cd(His)Ni(CN)₄]_n complexes show that the ground state of the unpaired electron in both complexes is dominantly d_x²-y².     

Synthesis,Crystal Structures,and Thermolysis Studies of Heteronuclear Transition Metal Aluminum Alcoholates

Heteronuclear alcoholate complexes [M{Al(OiPr)₄}₂(bipy)] ( 2-M , M = Fe, Co, Ni, Cu, Zn) and [M{Al(OcHex)₄}₂(bipy)] ( 3-M , M = Fe, Co, Ni, Zn) are formed by adduct formation of [M{Al(OiPr)₄}₂] ( 1-M , M = Fe, Co, Ni, Cu, Zn) with 2,2'-bipyridine and transesterification reaction with cHexOAc. According to crystal structure analyses, in 2-M and 3-M the central transition metal ion M²⁺ is coordinated by two chelating Al(OR)₄^– moieties and one bipyridine ligand in an octahedral arrangement. Treating 1-Cu with 2,2'-bipyridine leads to a reduction process, whereat the intermediate [Cu{Al(OiPr)₄}(bipy)₂][Al(OiPr)₄] ( 4 ) could be structurally characterized. During conversion of the iso-propanolate ligands in 1-Cu to cyclohexanolate ligands, Cu²⁺ is reduced to Cu⁺ forming [Cu{Al(O^cHex)₄}(py)₂] ( 5 ). UV/Vis-spectra and results of thermolysis studies by TG/DTA-MS are reported.     

Thermal, spectral and magnetic characterization of Co(II), Ni(II) AND Cu(II) 4-chloro-2-nitrobenzoates

Physico-chemical properties of 4-chloro-2-nitrobenzoates of Co(II), Ni(II), and Cu(II) were studied. The complexes were obtained as mono- and trihydrates with a metal ion to ligand ratio of 1:2. All analysed 4-chloro-2-nitrobenzoates are polycrystalline compounds with colours depending on the central ions: pink for Co(II), green for Ni(II), and blue for Cu(II) complexes. Their thermal decomposition was studied only in the range of 293–523 K, because it was found that on heating in air above 523 K 4-chloro-2-nitrobenzoates decompose explosively. Hydrated complexes lose crystallization water molecules in one step and anhydrous compounds are formed. The final products of their decomposition are the oxides of the respective transition metals. From the results it appears that during dehydration process no transformation of nitro group to nitrite takes place. The solubilities of analysed complexes in water at 293 K are of the order of 10^–4–10^–2 mol dm^–3. The magnetic moment values of Co²⁺, Ni²⁺ and Cu²⁺ ions in 4-chloro-2-nitrobenzoates experimentally determined at 76–303 K change from 3.89 to 4.82 μ_B for Co(II) complex, from 2.25 to 2.98 μ_B for Ni(II) 4-chloro-2-nitrobenzoate, and from 0.27 to 1.44 μ_B for Cu(II) complex. 4-chloro-2-nitrobenzoates of Co(II), and Ni(II) follow the Curie–Weiss law. Complex of Cu(II) forms dimer.     

Magnetic, spectral, and thermal behaviour of 2-chloro-4-nitrobenzoates of Co(II), Ni(II), and Cu(II)

Some physicochemical properties of 2-chloro-4-nitrobenzoates of Co(II), Ni(II), and Cu(II) were studied. The complexes were obtained as mono-and dihydrates with a metal ion—ligand mole ratio of 1: 2. All complexes are polycrystalline compounds. Their colours depend on the kind of central ion: pink for Co(II) complex, green for Ni(II), and blue for Cu(II) complexes. Their thermal decomposition was studied only in the range of 293 K–523 K because it was found that on heating in air above 523 K 2-chloro-4-nitrobenzoates decompose explosively. Hydrated complexes lose crystallization water molecules in one step. During dehydration process no transformation of the nitro group to nitrito one took place. Their solubilities in water at 293 K are of the orders of 10⁻³-10⁻² mol dm⁻³. The magnetic moment values of 2-chloro-4-nitrobenzoates determined in the range of 76 K–303 K change from 3.48μ_B to 3.82μ_B for Co(II) complex, from 2.24μ_B to 2.83μ_B for Ni(II) 2-chloro-4-nitrobenzoate, and from 0.31μ_B to 1.41μ_B for Cu(II) complex. 2-Chloro-4-nitrobenzoates of Co(II) and Ni(II) follow the Curie—Weiss law, but the complex of Cu(II) forms dimer.     

Anderson-type heteropolyanions of molybdenum(VI) and tungsten(VI)

The previously reported preparation of some Anderson-type molybdopolyanions containing divalent metal ions (Zn, Cu, Co or Mn) as a heteroatom has been reinvestigated. The molybdopolyanions of Zn(II) and Cu(II) were confirmed, although the Cu(II) polyanion was not stable and could not be recrystallized. On the other hand, the polyanions of Co(II) and Mn(II) could not be reproduced. Another type of heteropoly compound, [X(H₂O)_6-x(Mo₇O₂₄)]⁴⁻ [X = Cu(II), Co(II) or Mn(II)], was isolated as solids, which are not stable thermally. The mixed-type Anderson polyanions, [Ni(II)Mo_6-xW_x,O₂₄H₆]⁴⁻, which have been questioned as mixtures of species with different x values, were also reinvestigated using IR, UV absorption and MCD spectra. They are single species, but not mixtures, although some positional isomers may be present for the compounds where x = 2-4. The possibility of oxidation of the heteroatom with the Anderson structure maintained was examined. The oxidation of [Ni(II)Mo₆O₂₄H₆]⁴⁻ by the S₂O²⁻₈ ion in aqueous solution gave the Waugh-type [Ni(IV)Mo₉O₃₂]⁶⁻ polyanion, whereas the oxidation of [Ni(II)W₆O₂₄H₆]⁴⁻ gave no heteropoly compound.     

The relationship between the structures of Cu(II) complexes and their chemical transformations

The thermal dehydration of the compounds M ₂ ^I [M^II(H₂O)₆](SeO₄)₂, where M^I=NH₄, K, Rb, Cs and Tl, and M=Cu and Ni, was studied in order to correlate the course of the decomposition with the known crystal structures. It was found that the stoichiometry of the reactions is the same as that established for the analogous sulphato compounds of Cu(II) and Ni(II), respectively. Because of the discrepancies between the room-temperature crystal structures and the observed decomposition stoichiometries, high-temperature powder diffractograms were taken. These indicated structural changes of the copper(II) compounds during heating. The powder patterns for different structure changes were calculated and compared with the experimental ones. It was shown that during the heating two axial CuH₂O bonds are shortened and two equatorial bonds are lengthened. The observed decomposition stoichiometry is compatible with the formation of four nearly equal Cu-H₂O bonds. The activation energies (E^*) and pre-exponential factors (log A) for the first dehydration reaction of the Cu(II) compounds display the following sequence of M^I: Tl > Rb > NH₄ > K, and they are the higher, the shorter the split equatorial Cu(II) bonds. For the compounds of Ni(II) the sequence of E^* and log A values is K > Tl > NH₄ > Rb > Cs.

---

Zusammenfassung Zur Aufklärung des Zusammenhanges zwischen dem Zersetzungsweg und der bekannten Kristallstruktur wurde die thermische Dehydration der Verbindungen M ₂ ^I [M^II(H₂O)₆](SeO₄)₂ mit M^I=NH₄, K, Rb, Cs and Tl sowie mit m^II=Cu und Ni untersucht. Man fand für diese Reaktion die gleiche Stöchiometrie wie für die analogen Sulfatverbindungen von Cu(II) bzw. Ni(II). Wegen des Widerspruches zwischen der Kristallstruktur bei Raumtemperatur und der festgestellten Stöchiometrie der Zersetzungsreaktion wurden auch Pulverdiffraktionsaufnahmen bei höheren Temperaturen angefertigt. Bei Cu(II)-Verbindungen konnte während des Erhitzens eine Strukturänderung festgestellt werden. Für verschiedene Strukturänderungen wurden Pulveraufnahmen berechnet und mit den experimentellen verglichen. Es konnte gezeigt werden, da sich während des Erhitzens zwei axiale Cu-H₂O-Bindungen verkürzen und zwei äquatoriale Bindungen strecken. Die beobachtete Zersetzungsstöchiometrie entspricht der Bildung von vier anänhernd gleichen Cu-H₂O-Bindungen. Die Aktivierrungsenergie (E^*) und der präexponentielle Faktor (log A) und der ersten Dehydratationsreaktion der Cu(II)-Verbindungen sinken in folgender Reihenfolge für M^I:Tl, Rb, NH₄, K und sind umso größer, je kürzer die gespaltenen äquatorialen Cu(II)-Bindungen sind. Für Ni(II)-Verbindungen nehmen E^* und log A in folgenden Reichenfolge ab: K, Tl, NH₄, Rb, Cs.

     

Studies in nickel(IV) chemistry. Kinetics of the Cu(II) ion-mediated acid decomposition of tris(dimethylglyoximato) nickelate(IV) in aqueous acidic medium

Kinetics of the Cu(II) ion-mediated acid decomposition of tris (dimethylglyoximato)nickelate(IV), Ni(dmg)₃^2? (dmg^2? = dimethylglyoximate dianion), are reported in aqueous medium in the range of 3.6 ? pH ? 6.6 at 35°C and μ = 0.57 M. The pseudo-first-order rate constants of the disappearance of Ni(IV) k_obs(M) satisfy the equation where k_ad refers to the pseudo-first-order rate constants for the proton-assisted decomposition of the Ni(IV) complex determined independently and is a function of [H⁺], and k_dec(M) to that for the Cu(II) ion-mediated route and is a function of [H⁺] and [Cu²⁺]. Both k_obs(M) and k_dec(M) are found to increase with increasing [Cu(II)]₀, tending to attain limiting values at higher relative [Cu(II)]₀. At low [Cu(II)]₀ the k_dec(M) is found to register a decrease with increasing pH in the pH range of 3.6–4.4, then an increase in the range of 4.4–5.76, and again a decrease in the range of 5.76–6.6. Results on the Cu(II) ion-mediated acid decomposition are interpreted in terms of a probable mechanism involving pH-dependent adduct formation equilibria involving the one-protonated and the two-protonated species of Ni(IV) and the various species of Cu(II) ion in the media, followed by rate-determining acid decomposition of the adduct(s) to give Ni(II) aq. and Cu(dmgH)₂. While the two-protonated Ni(IV) complex apparently reacts about five orders of magnitude faster than the one-protonated species, the aquacopper(II) reacts about two orders of magnitude slower than the hydroxoaquacopper(II).     

On the relationship between the structures of CuII complexes and their chemical transformations

The thermal decomposition of the complexes M ₂ ^I Cu(SO₄)₂ · 6 H₂O and M₂Ni(SO₄)₂ · · 6 H₂O (M^I=NH₄, K, Rb, Tl) containing the complex cation M^II(H₂O)₆ ²+ (M^Il = =Cu, Ni) was studied. The values of the experimental activation energyE obtained for the dehydration reactions of both complex cations were found to be influenced in different ways by the outer-sphere cations present. It was therefore concluded that the activation energy of the decomposition of Cu(H₂O)₆ ²⁺ depends on the degree of tetragonal distortion of this cation, which increases with the ionic radius of cation M^I. TheΔH values of the studied reactions depend less on the structures of the coordination polyhedra.     

Octahedral CuII and NiII complexes manifesting with N′-[1-(pyridin-2-yl)ethylidene] acetohydrazide: Structural outlooks and spectral characteristics

A tridentate hydrazone precursor, N′-[1-(pyridin-2-yl)ethylidene]acetohydrazide (L) (1:1 refluxed product of acetichydrazide and 2-acetylpyridine), produced two octahedral Cu^II and Ni^II derivatives, [CuL₂]·NO₃ (1) and [NiL₂]·ClO₄·H₂O (2). Both are subjected to X-ray diffraction system, and structural investigation shows that the central metal atom (Cu^II or Ni^II) adopts a distorted octahedral geometry with N₄O₂ donor sets by coordination of a pair of independent hydrazone precursors. Besides X-ray study, IR and UV-vis spectra, thermal analysis and room temperature magnetic moments are utilized for establishing significant characteristics of both complexes. It is apparent that the M-N_pyridine bonds are slightly longer than the M-N_imino bonds, Cu1-N1 and Cu1-N4 [2.300(2) and 2.038(2) ?] for 1 and Ni1-N1 and Ni1-N4 [2.075(2) and 2.084(1) ?] for 2, Cu1-N2 and Cu1-N5 [2.062(1) and 1.932(1) ?] for 1 and Ni1-N2 and Ni1-N5 [2.008(2) and 1.975(2) ?] for 2, respectively. As per our observation, the effective magnetic moment value (μ_eff) is found to be 1.77 B.M. for 1 and 3.06 BM for 2, respectively.