Organische Komplexverbindungen des Molybdäns

Spengler, G.; Gänsheimer, J.

doi:10.1002/ange.19570691603

Cited by 19 publications

(5 citation statements)

References 22 publications

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“…This process was determined from the NMR studies to be important from about pH 6 to 9 and can be represented by 21 where M represents W and L represents the aminopolycarboxylic acid ligand. In the pH region above 6, no evidence was found for any Mo species containing fewer than three oxygen atoms, e.g., MoO 2 2+ , as has been proposed for other systems . The molybdenum-coordinating species in all the aminopolycarboxylic acid systems above pH 6 is MoO 3 , and by analogy, we have assumed that the corresponding coordinating unit in the tungsten systems is WO 3 .…”

Section: Complexation Of Tungsten(vi) With Ntamentioning

confidence: 79%

“…In the pH region above 6, no evidence was found for any Mo species containing fewer than three oxygen atoms, e.g., MoO 2 2+ , as has been proposed for other systems. 28 The molybdenum-coordinating species in all the aminopolycarboxylic acid systems above pH 6 is MoO 3 , and by analogy, we have assumed that the corresponding coordinating unit in the tungsten systems is WO 3 .…”

Section: Complexation Of Tungsten(vi) With Ntamentioning

confidence: 99%

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Dependence on Ionic Strength of Formation Constants, Protonation, and Complexation of Nitrilotriacetic Acid with Tungsten(VI) in Sodium Perchlorate Aqueous Solution

2004

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By use of potentiometric and spectrophotometric techniques, the complexation of tungsten(VI) with nitrilotriacetic acid (NTA) has been carried out in aqueous solution for pH = 7.5 at 25 °C and different ionic strengths ranging from (0.1 to 1.0) mol dm-3 (NaClO4). The composition of the complex was determined by the continuous variations method. It was shown that tungsten(VI) forms a mononuclear complex with NTA of the type (WO3L3-) at pH = 7.5. The dependence of the protonation of the aforementioned ligand and the stability constant of the complex on ionic strength is described by a Debye−Huckel-type equation. Finally the results have been compared with the previously reported data.

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Section: Complexation Of Tungsten(vi) With Ntamentioning

confidence: 79%

Section: Complexation Of Tungsten(vi) With Ntamentioning

confidence: 99%

Dependence on Ionic Strength of Formation Constants, Protonation, and Complexation of Nitrilotriacetic Acid with Tungsten(VI) in Sodium Perchlorate Aqueous Solution

2004

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“…Complexes of OMo 3+ usually show two low-intensity low-energy bands: The first one around 750 nm is agreed to belong to a b 2 * (4d xy , Mo−Cl π*) → e* (4d xz , yz , Mo−O π*) transition; the second one around 450−550 nm, however, was initially assigned to a b 2 * (4d xy , Mo−Cl π*) → b 1 * (4d x 2 - y 2 , Mo−Cl σ*) until Garner et al provided strong evidence that an e(O 2p xy , Mo−O π) → b 2 *(4d xy , Mo−L( cis ) π*) CT transition should be responsible . Its extinction coefficient varies for OMoCl 3 L 2 complexes from 20 to 80 M -1 cm -1 depending on the nature of L causing the compounds to be of either green or red-brown appearance [L 2 = β-diketonates, diphos, phen (brown), L = PPh 3 , OP(NMe 2 ) 3 , Cl, OPMe 3 , PMe 3 /OPMe 3 (green)]. However, in purple 4 this transition is extraordinarily high [ε = 1074 M -1 cm -1 ], supporting Garners theory.…”

Section: Resultsmentioning

confidence: 99%

The [Cl₂OMo(μ-OC₂H₅)₂(μ-HOC₂H₅)MoOCl₂]/PMe₃ System: A Chameleon Yielding the X-ray Structures of MoOCl₂(PMe₃)₃, MoOCl₃(PMe₃)₂, Mo₄O₄Cl₄(μ₂-OEt)₄(PMe₃)₂(μ₃-O)₂, and MoOCl₃(OPMe₃)(PMe₃)

et al. 1997

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The reaction of [Cl2OMo(μ-OC2H5)2(μ-HOC2H5)MoOCl2] (1) with 5 equiv of PMe3 provides a simple route to pure mer-MoOCl2(PMe3)3 (3), so that its crystal structure could be determined [C9H27Cl2MoOP3, monoclinic, P21/c, a = 17.138(3) Å, b = 12.808(3) Å, c = 19.226(4) Å, β = 115.99(1)°, Z = 8]. The mechanism of the conversion of 1 to 3 is complex, but one of the intermediates, MoOCl3(PMe3)2 (4), can be isolated and crystallized, if 1 is reacted only with 3 instead of 5 equiv of PMe3. 4 further reacts with an excess of PMe3 to yield 3, providing additional evidence for its intermediacy. The crystal structure of 4 could be determined [C6H18Cl3MoOP2, monoclinic, P21/n, a = 6.468(1) Å, b = 12.677(2) Å, c = 17.791(2) Å, β = 92.64(1)°, Z = 4]. If 4 is not isolated directly after the reaction and its crystallization is attempted from the raw mixture, two different compounds are obtained and their crystal structures were determined: MoOCl3(OPMe3)(PMe3) (5) [C6H18Cl3MoO2P2, monoclinic, P21/n, a = 6.783(3) Å, b = 12.623(4) Å, c = 18.298(8) Å, β = 98.58(3)°, Z = 4] and Mo4O4Cl4(μ2-OC2H5)4(PMe3)2(μ3-O)2 (6) [C14H38Cl4Mo4O10P2, monoclinic, P21/c, a = 1117.6(2) Å, b = 1161.6(2) Å, c = 1277.1(3) Å, β = 109.84(1)°, Z = 2]. 4 reacts slowly with CH2Cl2 producing [Me3PH]+[MoOCl4(PMe3)]- (7), which can also be found among the products of attempts to crystallize 4 from CH2Cl2/petroleum ether mixtures, while its treatment with an excess of HCl produces [Me3PH]2 +[MoOCl5]2- (8). The mechanism of the stepwise fragmentation of 1 yielding 3−7 is discussed.

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“…The Ross electrode system proved to be very stable showing drifts of 5 0.1 mV per day. The relationship between the measured potential E (in mV) and the concentration of free hydrogen ions at 25 "C is given by equation (1). Values for E and Ej were determined from…”

Section: Methodsmentioning

confidence: 99%

A potentiometric, spectrophotometric, and calorimetric investigation of molybdenum(VI)–oxalate complex formation

Cruywagen¹,

Heyns²,

Water³

1986

J. Chem. Soc., Dalton Trans.

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Complexation between molybdate and oxalate has been investigated in the pH, range 2.0-7.0 by potentiometric, spectrophotometric, and enthalpimetric titrations at 25 "C in 1 .O rnol dm-3 sodium chloride. The potentiometric data were treated with the computer program MINIQUAD taking into account side reactions of molybdate and oxalate with hydrogen ions. The 'best' reaction model comprises the three complexes (1,l ,2)2-, (2,2,5)3-, and (2,2,6)2with formation constants log f31,2 = 13.61 9, log = 31 20, and log Pm6 = 34.08; the numbers in parentheses refer to the values of p, q, and I in the general formula ( MOO:-)~(C~O:-)~( H + ) r . The spectrophotometric data were treated with the program SQUAD and the results obtained confirmed those obtained by potentiometry. The U.V. spectra of the complexes are reported. The enthalpy and entropy changes for complex formation were calculated from the enthalpimetric data using the values of the now known formation constants. The enthalpy values are: AHll2" = -59.5, AH,," = -1 23.0, and AH226" = -1 17.0 kJ mol-l. Equilibrium constants for the successive protonation of oxalate in 1 rnol dm-3 sodium chloride have also been determined, log = 3.52 and log pol* = 4.41.Complexes with a molybdate to oxalate ratio of 1 : 1, 1 : 2, 2: 1, and 2 : 2 have been reported to exist in the solid state as the salts of various monovalent cations.'-9 Of these compounds the compositions of only the 1 : 1 and 2 : 2 types, for which structural data are available, can be regarded as certain, for example H20.'v6 The isolation of compounds containing the complex and [ M o ~O ~( O H ) ( C ~O ~) ~] ~-, with [Co(en)J3' (en = ethylenediamine) as counter ion, have recently been reported by Beltran et al." They concluded that these complex anions also exist in solution and reported spectrophotometrically determined formation constants. A study of the thermal behaviour of the solids has also been reported.' 'Results of earlier investigations by various methods have been interpreted mainly in terms of the formation of only one complex with a molybdenum to oxalate ratio of 1 : 1.'2-'6 A recent potentiometric investigation l 7 in which the data were subjected to computer treatment showed that only one complex with stoicheiometry corresponding to M o O , ( C ~O ~) ~ -exists in the pH range 4-7. The results of the latter study contradict the findings of Beltran et a1.l' concerning the stoicheiometry of the predominant complex in solution.In this paper we present the results of a comprehensive investigation of molybdenum(vIjoxa1ate complex formation in the pH range 2-7. Computer treatment of potentiometric and spectrophotometric data led to the identification of three major complexes in solution and to the determination of their formation constants. The enthalpy and entropy changes for the formation of these complexes have also been determined. K2 EM020 5 ( c 2 04)2(Hz0)21 CNH41 2 CMo0 3(c2 O4)1* anions [Mo20,(OH)2(Cz04)2]4-, and

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Organische Komplexverbindungen des Molybdäns

Cited by 19 publications

References 22 publications

Dependence on Ionic Strength of Formation Constants, Protonation, and Complexation of Nitrilotriacetic Acid with Tungsten(VI) in Sodium Perchlorate Aqueous Solution

Dependence on Ionic Strength of Formation Constants, Protonation, and Complexation of Nitrilotriacetic Acid with Tungsten(VI) in Sodium Perchlorate Aqueous Solution

The [Cl₂OMo(μ-OC₂H₅)₂(μ-HOC₂H₅)MoOCl₂]/PMe₃ System: A Chameleon Yielding the X-ray Structures of MoOCl₂(PMe₃)₃, MoOCl₃(PMe₃)₂, Mo₄O₄Cl₄(μ₂-OEt)₄(PMe₃)₂(μ₃-O)₂, and MoOCl₃(OPMe₃)(PMe₃)

A potentiometric, spectrophotometric, and calorimetric investigation of molybdenum(VI)–oxalate complex formation

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Organische Komplexverbindungen des Molybdäns

Cited by 19 publications

References 22 publications

Dependence on Ionic Strength of Formation Constants, Protonation, and Complexation of Nitrilotriacetic Acid with Tungsten(VI) in Sodium Perchlorate Aqueous Solution

Dependence on Ionic Strength of Formation Constants, Protonation, and Complexation of Nitrilotriacetic Acid with Tungsten(VI) in Sodium Perchlorate Aqueous Solution

The [Cl2OMo(μ-OC2H5)2(μ-HOC2H5)MoOCl2]/PMe3 System: A Chameleon Yielding the X-ray Structures of MoOCl2(PMe3)3, MoOCl3(PMe3)2, Mo4O4Cl4(μ2-OEt)4(PMe3)2(μ3-O)2, and MoOCl3(OPMe3)(PMe3)

A potentiometric, spectrophotometric, and calorimetric investigation of molybdenum(VI)–oxalate complex formation

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The [Cl₂OMo(μ-OC₂H₅)₂(μ-HOC₂H₅)MoOCl₂]/PMe₃ System: A Chameleon Yielding the X-ray Structures of MoOCl₂(PMe₃)₃, MoOCl₃(PMe₃)₂, Mo₄O₄Cl₄(μ₂-OEt)₄(PMe₃)₂(μ₃-O)₂, and MoOCl₃(OPMe₃)(PMe₃)