Showing papers on "Aquation published in 1997"

Kinetics of the aquation of amminepentacyanoferrate(ii). a volume profile analysis

Abstract: The kinetics of the aquation and reverse formation reactions of Fe(CN)5NH33- were studied in detail. The reported activation parameters and volume profile strongly support the operation of a limiting D substitution mechanism.

cis-Diaminedichloroplatinum(II) Complexes Reversibly Linked into the Main Chain of Water-Soluble Polyamides

Abstract: As a follow-up study to previous work involving the platination of polyamide carriers through metal chelation by side group-incorporated ethylenediamine ligands, the present investigation is concerned with the synthesis of platinum-containing polymers in which the metal-coordinating ethylenediamine segments are components of the main chain Two chloro groups in cis geometry are attached to each Pt atom as additional ligands, complementing a square-planar cis-diaminedichloroplatinum(II) complex system The water-soluble polymeric carriers are synthesized by Michael-type addition polymerization, interfacial polymerization, and high-temperature solution polycondensation techniques and are crudely fractionated by stepwise aqueous dialysis, ultimately in tubing with a molecular mass cutoff of 25,000 Carrier platination is brought about by treatment with tetrachloroplatinate(II) anion in aqueous solution, care being taken to exercise strict control of reaction variables and workup conditions in an effort to restrict platination to the given ligands and avoid metal aquation or hydroxylation The platinum conjugates, with Pt contents ranging from about 11 to 23% by mass, are completely soluble in aqueous media when freshly prepared, although long-term storage at room temperature in the solid state is conducive to gradual loss of solubility The conjugates are of interest as carcinostatic agents

Reactivity and solvatochromism of pentacyanoferrate(II) complexes in diol–water mixtures

Abstract: Rate constants are reported for substitution at the pentacyanoferrate(II) ions [Fe(CN)5L]3−, where L=3,5-dimethylpyridine or 3-cyanopyridine, in binary aqueous mixed solvents containing up to 60vol% 1,2-ethanediol, 1,2-butanediol, methanol or ethanol Trends for diol-containing mixtures are compared with those for monohydroxylic alcohols, and the reactivity pattern for these complexes is compared with those established earlier for base hydrolysis of tris(1,10-phenanthroline)iron(II) and for the aquation of cis-dichloro-bis- (1,2-ethanediamine)cobalt(III) The solvatochromic behaviour of several pentacyanoferrate(II) ions has been established in binary aqueous mixtures containing 1,2-ethanediol, 1,2-butanediol, 1,4-butanediol and 1,2-pentanediol A correlation between reactivity and solvatochromism is presented

Thermal and photochemical reactions of bis(diamine)(sulfito)cobalt( III ) complexes: effect of chelate-ring size

Abstract: The kinetics of formation of cis-[Co(tn) 2 (OH 2 )(OSO 2 -O )] + (tn = 1,3-diaminopropane), its acid-catalysed aquation to the parent diaqua complex, anation of trans-[Co(tn) 2 (OH 2 )(SO 3 - S)] + by N 3 - , NCS - , SO 3 2- –HSO 3 - , anation of trans-[Co(tn) 2 (OH)(SO 3 -S )] by SO 3 2- and acid-catalysed aquation of trans-[Co(tn) 2 (SO 3 -S) 2 ] - to the corresponding (aqua)(sulfito-S) complex were investigated and the results compared with analogous data for the corresponding 1,2-diaminoethane (en) complexes. Expanding the chelate-ring size from five to six had virtually no effect on the rate of formation of the sulfito-O complex, but retarded its acid-catalysed aquation. The latter effect was attributed to a pK perturbation; intramolecular hydrogen bonding between the co-ordinated H 2 O and sulfite in cis-[Co(tn) 2 (OH 2 )(OSO 2 -O )] + hindered the protonation pre-equilibrium of the sulfito-O complex involved in the acid-catalysed aquation. This is further supported by the fact that there was no ring-size effect on the acid-catalysed aquation of trans-[Co(L–L) 2 (OH 2 )(OSO 2 ) ] + (L–L = tn or en). The strong labilising action due to chelate-ring expansion is remarkably attenuated by the trans effect of S-bonded sulfite as observed in the anation of trans-[Co(L–L) 2 (OH 2 /OH)(SO 3 -S)] +/0 . However, trans-[Co(tn) 2 (OH 2 )(SO 3 - S)] + was found to be prone to intramolecular electron transfer between Co III and S IV under thermal conditions unlike its en analogue, further reflecting the ring-size effect. Flash photolysis of trans-[Co(L–L) 2 (OH 2 )(SO 3 -S)] + (L–L = en or tn) generated the transient trans-[Co(L–L) 2 (OH 2 )(OSO 2 )] + . The photochemical ligand isomerisation of both complexes (Co III –SO 3 + → Co III –OSO 2 + ) also occurred at comparable rates [k iso = (4.1 ± 0.8) × 10 4 and (3.2 ± 1.3) × 10 4 s -1 at 25 °C for the en and tn complexes respectively]. Steady-state photolysis at 254 nm indicated that trans-[Co(en) 2 (OH 2 )(SO 3 -S )] + underwent photoaquation and photoreduction. Strikingly photoreduction could not be detected for this complex at pH > 8.

A temperature-dependent dynamic rearrangement of cis-(R,S)-[Pd(egta)]2– (egta4–=glycine, N,N′-(1,2-ethanediylbis(oxy-2,1-ethanediyl)bis[N-carboxymethyl]) in aqueous solution

Abstract: The cis-(R,S)-[Pd(egta)]2– complex, egta4–=glycine, N,N′-(1,2-ethanediylbis(oxy-2,1-ethanediyl)bis[N-carboxymethyl]), has been examined by 1H- and 13C-n.m.r. methods over the 18.0 to 95.0°C range in D2O. A dynamic process occurs above 65°C which makes the protons on the NCH2 functionalities of the egta tether become 1H-n.m.r. equivalent. The two states that interconvert coalesce at 81°C. Evidence from 13C-n.m.r. spectra obtained at 81°C show that the in-plane coordinated carboxylates are not lost, but rather a pendant carboxylate becomes attached with loss of the central imino donor. The resultant palladium(II)NO3 intermediate is able to reform cis-(R,S)-[Pd(egta)]2– or, presumably, give trans-(R,R)-[Pd(egta)]2–. The rate limiting step occurs with a rate constant of 178s–1 at 81°C and an activation energy of 20.5kJ/mol. However, competitive aquation of glycinato donors above 85°C prevents isolation of a stable trans-(R,R)-[Pd(egta)]2– isomer.

Kinetic studies on spontaneous ligand substitution in [Cr(S-pdtra)(H2O)]–NCS– and [Cr(edtrp)(H2O)]–NCS– systems

Abstract: The kinetics of anation of [Cr(S-pdtra)(H2O)] and [Cr(edtrp)(H2O)] complexes (S-pdtra=S-propane-1,2-diamine-N,N,N′ -triacetate, edtrp=ethylenediamine-N, N,N′-tripropionate) by thiocyanates and aquation of the [Cr(NCS)(S-pdtra)]– and [Cr(NCS)(edtrp)]– ions have been studied in aqueous HClO4 solutions. The rate laws and the activation parameters have been determined and discussed. The observed decrease in reactivity for the edtrp complexes corresponds with a changeover of the reaction mechanism from Ia to Id for reactions of the CrIII-S-pdtra and CrIII-edtrp species, respectively.

The kinetics and mechanism of aquation and base hydrolysis of the cis-[Co(cyclen)Cl2]+ cation (cyclen=1,4,7,10-tetraazacyclododecane)

Abstract: The aquation of cis-[Co(cyclen)Cl2]+ (cyclen=1,4,7,10-tetraazacyclododecane) has been studied over a range of temperatures with 0.1 mol dm–3 HNO3 as solvent. At 25°C, kaq=4.5×10–3 s–1 with ΔH‡=78 kJ mol–1 and ΔS‡298=−21 J K–1 mol–1. Base hydrolysis of cis-[Co(cyclen)Cl2]+ is extremely rapid with kOH=2.1×107 dm3 mol–1 s–1 at 25°C and I=0.1 mol dm–3. This is the largest rate constant so far reported for the base hydrolysis of a cis-dichloro-complex of a saturated macrocycle. The activation parameters, ΔH‡=53 kJ mol−1 and ΔS‡298=73 J K–1 mol–1 are consistent with a mechanism in which deprotonation of the substrate is rate-determining. This conclusion is confirmed by the observation of general base catalysis by formate ion. The Bronsted β value for the reaction is ca. 0.72 and SN1(CB) and E2 mechanisms are considered to account for the kinetic results. Base hydrolysis of cis-[Co(cyclen)(OH)Cl]+ has also been studied in the pH range 6.5 to 8.7. The value of kOH=3.8×102 dm3 mol–1 s–1 at 25°C and I=0.1 mol dm–3 with ΔH‡=110 kJ mol–1 and ΔS‡298=171 J K–1 mol–1 are consistent with an SN1(CB) mechanism.

Kinetics of aquation of trans-dichlorobis(N,N′-dimethylethylenediamine)cobalt(III) ion in water–methanol in water–propan-2-ol media

Abstract: The complex trans-[Co(dmen)2Cl2]Cl (dmen=N,N′-dimethylethylenediamine) has been prepared and characterized by elemental analysis, u.v.-vis. and i.r. spectra. The kinetics of the primary aquation of trans-[Co(dmen)2Cl2] in H2O, H2O–MeOH and H2O–i-PrOH have been examined over a wide range of solvent compositions and temperatures (40–55°C). Plots of rate constants (log k) versus the reciprocal of the dielectric constant of the medium (Ds−1) and Grunwald–Winstein values of the solvent (Y) were found to be non-linear. The variation of enthalpies (ΔH‡) and entropies (ΔS‡) of activation with solvent composition has been determined. Plots of ΔH‡ or ΔS‡ versus the mole fraction of each solvent exhibit extrema at x2=ca. 0.16 and 0.27 for MeOH and at x2=ca. 0.03 and 0.14 for i-PrOH. Furthermore, the cycle relating the free energy of activation in H2O to that in H2O–co-solvent shows that the stabilizing influence of the changes in the solvent structure is greater on the emergent five-coordinate cation in the transition state than that on the complex ion in the initial state, with the difference becoming greater as the mole fraction of the co-solvent increases.

Kinetics and mechanism of H+(aq)-assisted aquation of [Cr(N3)(S-pdtra)]− and [Cr(N3(edtrp)]−ions

Abstract: Two new complex anions, [Cr(N3)(S-pdtra)]− and [Cr(N3)(edtrp)]−, were obtained in solution by N3−/HN3 anation of the aqua analogues (S-pdtra = S-propane-1,2-diamine-N,N,N′-triacetate, edtrp = ethylenediamine-N,N,N′-tripropionate). Aquation of these species in acidic media leads to the same geometrical isomers as those used for the synthesis. The aquation rate is strongly dependent upon [H] and is substantially higher in D2O than in H2O. Protonation of the coordinated azide was not observed spectrophotometrically. The rate law and activation parameters have been determined and discussed.

The sensitization of the ligand-field state of the hexaammineruthenium(II) complex ion by organic compounds

Abstract: The sensitilized photolysis of [Ru(NH3)6]2+ by the organic dye rhodamine B and biacetyl was studied under conditions in which only the sensitizer absorbs. The reaction products resulting from ammonia aquation and Ru(II) to Ru(III) oxidation are the same for direct and sensitized photolysis. The energy transfer rate constant, calculated from te fluorescence quenching of rhodamine B, is similar to the estimated from the limiting quantum yield of the photosensitized photoaquation of the complex. Both reactions originate from a common reactive low-lying ligand-field (LF) state, which is also responsible for the direct photolysis reactions. This state, which leads directly to photoaquation, seems to have a certain charge transfer to solvent (CTTS) character, which is responsible for the photo-oxidation products. Sensitization is effective with rhodamine B (17 450 cm−1) and biacetyl (19 000 cm−1), whereas no reaction is observed with neutral red (16 900 cm−1). These results show that the excited state responsible for the photochemical reactions lies in the energy range between 16 900 cm−1 and 17 700 cm−1 and possesses spin-orbit character.

Heterogeneous effects on the thermal and photoreactivities of tris(1,2-diaminoethane)chromium(III) cation and hexathiocyanatochromate(III) anion in aqueous media

Abstract: The ground- and excited-state reactivities of the [Cr- (en)3]3+ (en=1,2-diaminoethane) and [Cr(NCS)6]3− ions in a polyacrylamide (PAA) environment are reported. The aquation kinetics of these complexes has been studied to identify the effect of added PAA with varying molecular weight. Aquation of the complexes in aqueous acid containing PAA yielded the respective substituted products. The macromolecule in solution was found to decrease significantly the rate of ligand replacement. Similarly, photolysis of the cationic and anionic complexes in water–PAA mixtures revealed a decrease in aquation quantum yield. Possible explanations for the decrease in reaction rates and quantum yields are discussed.

Reactions of cis-(aqua)(amine)bis(ethylenediamine)cobalt(iii) complexes with sulfur(iv) in aqueous medium

Abstract: The kinetics of the formation/acid-catalysed aquation (SO2 elimination), CoIII-OSO2+→CoIII-SO3+ isomerization, intramolecular reduction and base hydrolysis of the O-bonded sulfito complexes, cis-[Co(en)2(RNH2) (OSO2)]+ (en=ethylenediamine; R=H, Me, Et, PhCH2 and C6H11) have been investigated. The spontaneous and base-catalysed isomerization involve loss of monodentate amine ligands from the CoIII centre to give trans-[Co(en)2(SO3-S)2]– (in excess SO32–) or trans-[Co(en)2(OH)(SO3-S)] (under base hydrolysis conditions). This result is presumably associated with a cis-labilizing action of the O-bonded sulfite. Steric retardation is observed for the formation and acid-catalysed aquation of the O-sulfito complex, the effect being relatively larger for the latter reaction. Steric acceleration is observed in the isomerization and intramolecular reduction and base hydrolysis of the O-sulfito complexes.¶ The trans-S-disulfito complex is prone to fast H+-catalysed aquation {k=(1.52±0.06)×104 dm3 mol–1 s–1, ΔH‡=81 ± 2 kJ mol–1, ΔS‡= 108 ± 5 J K–1 mol–1 at 25°C, I = 1.0 mol dm−3} yielding trans-[Co(en)2 (SO3-S)(OH2)]+.

Ligand control on the reactions of oxygen- and sulphur-bonded (sulphito)pentaminecobalt(III) complexes in solution

Abstract: The kinetics of formation, acid-catalysed aquation, ligand isomerisation (CoIIIOSO2+→CoIIISO3+), intramolecular electron-transfer, and base-catalysed hydrolysis and isomerisation of O-bonded sulphito complexes, cis-[Co(en)2(B)(OSO2–O)]+[B=benzimidazole (bzimH), N-methylimidazole (N-meim)] and the anation of cis-[Co(en)2(B)OH)]2+ [B=bzimH, N-meim and imH (imidazole)] by oxSO2−3 are reported. Steric acceleration is observed in the formation and acid-catalysed aquation of the O-sulphito complexes. The ligand isomerisation leads to loss of the monodentate amine with the formation of trans-[Co(en)2(SO3–S)2]− (in an excess of sulphite). Steric acceleration is more pronounced in the isomerisation and base hydrolysis than in the redox process. The results indicate cis labilisation of the coordinated O-sulphite. The [(tetraethylenepentamine)Co(OSO2–O)]+ cation undergoes base hydrolysis 103 times faster than the corresponding (en)2(B) complexes; base-catalysed ligand isomerisation for the former is not observed unlike in the latter. The anation of cis-[Co(en)2(B)OH]2+ (B=imH, bzimH, N-meim) by SO2−3 in a mild alkali pH range (pH=7.9–9.6) and in an excess of SO2−3, yields exclusively trans-[Co(en)2(SO3–S)2]− with no evidence for the formation of the cis-[Co(en)2(B)(SO3–S)]+ or its O-sulphito analogue. The intramolecularly generated amido conjugate base of the sulphite ion-pair, {cis-[Co(en)2(B)OH]2+,SO32−}.41cm{cis-[Co(en)(en-H) (B)- OH2]2+,SO32−}, is believed to generate a five-coordinate intermediate (TBP) that captures the S-end of SO2−3 selectively from a site trans-to the amine B so that the amine is labilised by the trans effect of the sulphite. The NH-deprotonated coordinated imidazolate or benzimidazolate species, cis-[Co(en)2(bzm/im)OH]+, do not undergo anation by SO2−3.

Effect of cosolvent hydrophobicity on the aquation of cis- and trans-chloro(nitro)bis(ethylenediamine)cobalt(III) ions

Abstract: The kinetics of aquation of cis- and trans-[Co(en)2NO2Cl]+ have been investigated in aqueous mixtures of 2-methoxyethanol, 2-ethoxyethanol, isopropoxyethanol, 2-butoxyethanol, 1,2-dimethoxyethane, ethylene glycol and n-propanol over a range of temperatures. The results are discussed in terms of the hydrophobic effect in these systems.