S. I. Ali

Photoexcitation of octacyano complexes of molybdenum(IV) and tungsten(IV) with ethylene diamine. Kinetics and reaction mechanism

SummaryThe kinetics of thermal reactions of photochemically generated aquaheptacyano MoIV and WIV complexes and their protonated and deprotonated forms have been studied spectrophotometrically in buffer solutions at pH 5.0–10.0, and ionic strength, 8×10−2 M at 25°C. A reaction scheme for the photochemical and thermal reactions of the MoIV and WIV octacyano complexes with ethylene diamine is proposed. Rate constants and quantum yields for these systems are maximal at pH 8.0. At pH>8.0, the reverse reaction, generating octacyano complexes from heptacyano species, is faster; at low pH the ligand is protonated and is less reactive. Quantum yields are higher for Mo than for W owing to the shorter life time of excited state species. This is because physical deactivation is expected to be more rapid in the heavier element due to enhanced spin-orbit coupling. Furthermore Mo-induced splitting is larger in [W(CN)8]4− as compared to [Mo(CN)8]4− which results in greater bond strength for tungsten.

Photosubstitution reactions in potassium octacyanomolybdate(IV) and octacyanotungstate(IV) in the presence of 1,10-phenanthroline and 2,2-́bipyridyl

Abstract Substitution reactions take place following the photonic excitation of aqueous K4M(CN)8 (where M = Mo or W) in the presence of 1,10-phenanthroline and 2,2 - bipyridyl. Changes in absorbance with time show that the overall reaction is dependent on photochemical activation of potassium octacyanomolybdate(IV) and -tungstate(IV). The species [K2Mo(CN)4(OH)2(phen)], [K2W(CN)4(OH)2(phen)], [K2Mo(CN)4(OH)2(bipy)] and [K2W(CN)4(OH)2(bipy)] exist in solution. The final photosubstitution products [Mo(OH)3(CN)(phen)2] · 2H2O], [Mo(OH)3(CN)(bipy)2] · 3H2O, [W(OH)3(CN)(phen)2] · 2H2O and [W(OH)3(CN)(bipy)2] · H2O have been isolated in the solid state. Their IR spectra have been discussed. The quantum yield of the photosubstitution reactions has been determined and its variation with change of concentration of the complex as well as the H+ ion concentration has been studied.

Characterization, kinetics and mechanism of thermal decomposition of photosubstituted ethylenediamine complexes of molybdate(IV) and tungstate(IV) with chromium(III)

Abstract Photoinitiated substitution complexes of [M(CN)8]4− (where M= Mo(IV) or W(IV)) and ethylenediamine with chromium(III) have been synthesized and characterized. On the basis of elemental analysis, the complexes have been assigned formulas as folows: Cr[Mo(CN)(C 2 H 8 N 2 )(OH) 6 ]·2H 2 O I for Mo(IV); and Cr[W(C 2 H 8 N 2 )(O 2 )(OH) 3 ]·H 2 O II for W(IV) The characteristic IR absorption peaks for different entities present support the assigned formulas. Complex I shows the absorption peaks due to ν(CN) stretching bond, NH asymmetric deformation, NH symmetric deformation and NH3 rocking mode showing the presence of cyanide and ethylenediamine. The loss of the absorption peak due to ν(CN) stretching in the spectra of complex II confirms the substitution of all the cyanide ligands. The thermal degradation of the complexes has been studied by TG and DSC techniques. Both the complexes have a similar thermal decomposition behavior: involving expulsion of water molecules in the first step followed by the expulsion of other ligands. Kinetics and a thermal decomposition mechanism have been proposed for each complex. Thermodynamic parameters such as activation energy (Ea), pre-exponential factor (A) and entropy of activation (ΔS#) have been calculated for each step, employing different integral methods of Doyle, Coats and Redfern, and Arrhenius. The reaction enthalpy is obtained from DSC data

Thermal, spectroscopic and kinetic characterization of reaction products of copper(II) chloride with photoproducts of octacyanocomplexes of Molybdenum(IV) and Tungsten(IV) with ethylenediamine

Abstract The thermal dissociation of complexes formed by copper(II) chloride with photoproducts of M(CN) 4− 8 [where M=Mo or W] and ethylenediamine has been studied by thermogravimetry (TG), differential scanning calorimetry (DSC) and IR spectroscopy. The observed IR bands for different groups support the assigned composition. Both Mo(IV) and W(IV) show the same stoichiometric behaviour towards complex formation but a different decomposition behaviour. In case of Mo(IV) decomposition takes place in four steps with cyanide and oxide of copper and tetrachloro molybdenum(IV) as residue, while in case of W(IV) the decomposition occurs only in three steps up to 298°C. The copper cyanide along with tetrachloro tungstate(IV) is found as residue. DSC for Mo complex displays four transitions, two exothermic and two endothermic. In case of W, DSC displays three endothermic transitions corresponding to three decomposition steps with three different Δ H values. On the basis of TG and DSC, mechanism for decomposition of each complex has been proposed. Kinetic parameters like activation energy ( E a ), frequency factor ( A ), entropy of activation (Δ S # ) for each step has been calculated involving differential methods like Doyle, Coats and Redfern and Arrhenius. The heat of the reaction is obtained from DSC curves.

Snythesis, characterization and thermal dissociation of cobalt(II) complexes of the photoproducts of octacyanomolybdate(IV) and -tungstate(IV) with ethylenediamine

Abstract Photosubstituted mixed ligand complexes of Co(II) with irradiated solutions of Mo(CN) 8 4− and W(CN) 8 4− with ethylenediamine have been synthesized. The complexes have been isolated and characterized by their elemental analysis and IR spectroscopy. The assigned formulae are Co 2 [Mo(CN) 2 (C 2 H 8 N 2 ) 2 (OH) 2 ]Cl 4 .2H 2 O I and Co[W(CN) 2 (C 2 H 8 N 2 ) 2 (OH) 2 ]Cl 2 .2H 2 O II for Mo(IV) and W(IV) complexes, respectively. The IR peaks observed for both the complexes show N–H stretching, H–N–H bending and stretching vibrations of the C–N and C–C bonds. Depending on the nature of the absorption bands, complex I is assigned as - trans and complex II as - cis configuration. The thermal decomposition of these complexes has been studied by TG and DSC techniques. The reaction scheme for decomposition of each complex has been proposed. The activation energy ( E a ), pre-exponential factor ( A ) and entropy of activation (Δ S # ) have been calculated by employing the integral methods like Arrhenius, Coats–Redfern and Doyle. Enthalpy (Δ H ) values for each transition are obtained from DSC data.

Photocatalytic system: kinetics and mechanism of the photoreactions of octacyano complexes of molybdenum(IV) and tungsten(IV) with 1,2,3-indane-trione-hydrate

Abstract The ligand field excitation of octacyano complexes of molybdenum(IV) and tungsten(IV) produces [M(CN)7OH]4− and a free cyanide ion. [M(CN)7OH]4− (M = Mo, W) reacts with 1,2,3-indane-trione-hydrate (ninhydrin) in 1:1 stoichiometry. The rate constants and quantum yields are at a maximum at pH 8.0. The rate of the reaction and the quantum yield increase with an increase in the ligand concentration and decrease with an increase in [M(CN)8]4− concentration. Quantum yields are higher for molybdenum than for tungsten owing to the shorter lifetime of the excited state species. This is because physical deactivation is expected to be more rapid in the heavier element due to enhanced spin—orbit coupling. Furthermore, molecular-orbital-induced splitting is larger in [W(CN)8]4− than in [Mo(CN)8]4− which results in a greater bond strength for tungsten.

Kinetics and mechanism of the interaction of hexaaquochromium(III) with octacyanomolybdate(IV) ions

Abstract The kinetics of the interaction of hexaaquochromium(III) ion with potassium octacyanomolybdate(IV) have been studied using conductance and spectrophotometric data. The mechanism of the reaction is discussed and the effect of H+ ion and the ionic strength on the rate of the reaction determined. The reaction is found to be pseudo-first order with respect to potassium octacyanomolybdate(IV) and inverse first order with [H3O+]. The rate of the reaction increases with increase in ionic strength and temperature. Activation parameters have been calculated using the Arrhenius equation and have the values ΔE* = 1.3 × 102 kJ mol−1, ΔH* = 129 kJ mol−1, ΔS* = −315 e.u., ΔF* = 2.3 × 102 kJ and A = 1.5 × 10−3. The mechanism proposed is based on ion-pair formation and the rate equation obtained is given by: kobs= [ kK E [H 3 O + ]+ k′K′k E k h ][Mo(CN) 8 4− ] [H 3 O + ]+ k h +[ K E [H 3 O + ]+ K′ E k h ][Mo(CN) 8 4− ]

Photoreactivity of octacyanotungstate (IV) with 1,2,3-benzotriazole; kinetics and mechanism of the reaction

Abstract The kinetics of the reactions of photochemically generated [W(CN) 7 OH] 4− with 1,2,3-benzotriazole were studied in buffer solutions of pH 5.8-10.7 at an ionic strength of 0.1 M at 25±0.2 °C. The quantum yield for formation of the photoproduct was calculated and was found to be dependent on the pH and ligand and [W(CN) 8 ] 4− concentrations. A reaction scheme for the photochemical reaction of [W(CN) 8 ] 4− and 1,2,3-benzotriazole is proposed. Rate constants and quantum yields are at a maximum at pH 8.7. At pH⪢ 8.7, the reverse reaction, generating octacyano complexes from heptacyano species, is faster; at low pH the ligand is protonated and is less reactive. At high concentrations of [W(CN) 8 ] 4− , first-order kinetics are obeyed, which fall off at low concentrations of [W(CN) 8 ] 4− to give eventually a second-order rate constant. The ionic strength does not affect the reaction rate, implying that the mechanism is not dissociative.

Synthesis and thermal behaviour of adducts of [Mo(CN)8]3− and [W(CN)8]3− with 8-hydroxyquinoline

The adducts of [Mo(CN)8]3− and [W(CN)8]3− with 8-hydroxyquinoline (oxine) synthesized were of the type K3[Mo(CN)8]·(C9H7ON)8·4H2O and K3[W(CN)8]·(C9H7ON)6·3H2O. The FTIR spectra show the presence of the (CN) and oxine group in the adduct compounds through the peaks in the range 2047–2108 cm−1 and 1015–1461 cnf−1 respectively. The lower region of FTIR spectra show the M=O stretching while the higher range to v(N-H) and v(OH) modes. The uncoordinated water in these adducts was removed at around 110°C in a single step. The decomposition of adduct compounds starts from 125°C and continues to higher temperatures upto 850°C in different stages. The second stage of decomposition was predominant with the removal of oxine molecules with the formation of polymeric oxide of the type K2O·M2O5 (whereM=Mo or W) obtained as the pyrolysis product.ZusammenfassungDie hergestellten Addukte von [Mo(CN)8]3− und von [W(CN)8]3− mit 8-Hydroxyquinolin (Oxin) haben die allgemeine Formel K3[Mo(CN)8](C9H7ON)8·4H2O bzw. K3[W(CN)8](C9H7ON)6·3H2O. Die FTIR-Spektren beweisen die Gegenwart der (CN)- bzw. der Oxingruppen in den Adduktverbindungen durch die Peaks im Bereich 2047–2108 cm bzw. 1015–1461 cm−1. Die untere Region des FTIR-Spektrums zeigt die M=O Valenzschwingung, die obere Region (N-H) und (OH). Nichtkoordiniertes Wasser wird in diesen Addukten in einem einzigen Schritt bei 110°C abgegeben. Die Zersetzung der Adduktverbindungen beginnt bei 125°C und setzt sich in verschiedenen Schritten bis hin zu 850°C fort. Der zweite Schritt der Zersetzung wird durch die Abgabe von Oxinmolekülen beherrscht, wobei polymere Oxide der allgemeinen Formel K2OM2O5 (mitM= Mo oder W) als Pyrolyseprodukte erhalten werden.

Stability constants and protonation constants of tetracyano bis(phenanthroline) molybdate(iv) and tetracyano bis(bipyridyl) molybdate(iv)

Abstract 1,10-Phenanthroline (phen) and 2,2′-bipyridyl (bipy) form 2:1 complexes with the dioxotetracyanomolybdate(IV) ion by substitution reactions. The stepwise stability constants and the protonation constants of the subtituted products Mo(CN) 4 (phen) 2 and Mo(CN) 4 (bipy) 2 have been calculated using spectrophotomeric and potentiometric methods. Two successive protonation steps have been found for these systems. Concentration protonation constants have been determined at different ionic strengths and the thermodynamic protonation constants were evaluated by extrapolation to infinite dilution. The dependence of log K p n (where n = 1.5 or 3.0) on ionic strength is given by the equation log K p n = log T K p n + B √ I /(1 + √ I ). Thermodynamic parameters for the complex formation have been calculated and the results have been discussed. The protonated products have been isolated and analysed.