Willem E. Renkema

Square planar complexes of nickel(II), palladium(II) and platinum(II) with 1-(2-hydroxyphenyl)-3,5-diphenylformazan

SummaryA novel series of formazan complexes of general formula FoML [H2Fo = 1-(2-hydroxyphenyl)-3,5-diphenylformazan; M = NiII, PdII or PtII; L = NH3, py and Ph3P] are described. The formazan nickel(II) system shows linkage isomerism; one isomer, A, contains an unusual five-membered formazan chelate ring, whereas the other, isomer B, has the usual six-membered ring.13C n.m.r., u.v. and i.r. spectra are presented and interpreted. From these the palladium and platinum complexes appear to contain the six-membered ring of the B type isomer.

Base hydrolysis of mono-alkylsubstituted chloropentaamminecobalt(III) complexes

SummaryThe preparation of the series ofcis- andtrans-[Co(NH3)4(RNH2)Cl]2+ complexes (withcis, R = Me orn-Pr andtrans, R = Me, Et,n-Pr,n-Bu ori-Bu) is described. The u.v-visible spectra indicate a decrease of the ligand field on increasing chain length. Infrared spectra show an enhanced Co-Cl bond strength compared to the pentaammine. Partial molar volumes of the complex cations do not reveal steric compression. From proton exchange studies in D2O it follows that [Co(NH3)5Cl]2+ and thecis- andtrans-[Co(NH3)4-(CH3NH2)C1]2+ complexes exchange the amine protons on the grouptrans to the chloro faster than those on thecis. A coordinated methylamine group exchanges its amine protons slower than a corresponding NH3 group in the parent pentaammine, but the methyl introduction accelerates the exchange of the other NH3 groups. The aquation of thetrans-alkylamine complexes (studied at 52° C) is acceleratedca. 10 times compared to the parent pentaammine, irrespective of the nature of the alkyl group. Thecis complexes do not show this acceleration of aquation. In base hydrolysis (studied at 25° C) thecis complexes are the most reactive (a factor 20 over the parent ion). Thecis/trans product ratio in base hydrolysis and the competition ratio in the presence of azide ions were calculated from the 500 MHz1H n.m.r. spectra, which display distinctly different alkyl resonances for each individual complex. Thecis ions react under stereochemical retention of configuration; thetrans compounds give 10±1%trans tocis rearrangement. The ionic strength (⩽4 mol dm−3) and the pH do not affect this result. The same product ratio is obtained in methanol-water and DMSO-water mixtures. Ammoniation in liquid ammonia gives the same ratios as in base hydrolysis, base-catalyzed solvolysis in neat methylamine gives stereochemical retention for both thecis- andtrans-methylamine ion. The product competition ratio (Co-N3)/(Co-OH2) for thecis compounds and the bulkier amines (R =n- andi-Bu), 15–25% at 1 mol dm−3N3−, isca. twice that of thetrans compounds and the pentaammine. The results are interpreted in the classical conjugate base mechanism, and discussed in the context of current ideas about stereochemistry of base hydrolysis.

Nitrito–nitro linkage isomerisation of the penta-amminecobalt(III) complex in liquid ammonia

The nitrito–nitro linkage Isomerisation reaction of the penta-amminecobalt(III) complex in liquid ammonia proceeds entirely via an intramolecular conjugate-base mechanism. The reaction is fully retentive and the penta-ammine(nitro)cobalt(III) complex is the only species that could be detected by 1H n.m.r. after the reaction was completed. The advantage of liquid ammonia as solvent is demonstrated by the separate determination of the pre-equilibrium constant Kc.b(ΔH= 27 kJ mol–1; ΔS=–14 J K–1 mole–1) and the rate constant of the rate-determining step k2(ΔH‡= 78 kJ mol–1; ΔS‡= 29 J K–1 mol–1). Comparison of the activation parameters of the latter rate constant with the activation parameters reported earlier for the ammoniation reactions of a number of cobalt(III) and rhodium(III) amine complexes in liquid ammonia shows the expected deviation from a limiting dissociative activation.

Electrochemistry of solutions in liquid ammonia. Part VII. The use of glass electrodes for ammonium and sodium cations as ion-selective sensors at −40 °C

The behavior of Li/La glass electrodes as specific ion sensors for NH4+ and Na+ cations in liquid ammonia solutions at −40°C has been assessed using concentration cells with transference. The measurement of emfs of cells with very high resistances due to glass at −40°C has been overcome partly by the use of thinly blown Li/La glass and mainly through the design and use of a ‘floating shield’ emf measuring system. For solutions of NH4NO3, NH4I, NH4BF4, and NH4Cl almost linear pNH4 vs. emf responses were observed between pNH4 0 and 5; for NH4NO3 solutions the slope (40±1 mV/pNH4) was invariant for substantial increases in Na+ concentrations. Solutions of NaNO3, NaCN, NaClO4, NaNCS, NaN3, and NaNO2 gave almost linear pNa vs. emf responses but the slopes were markedly dependent upon the NH4+ concentration. Estimates of the mean molal ion activity coefficients for nitrate solutions were obtained from earlier transference data: γ±(NaNO3)=0.14±0.02 and γ±(NH4NO3)=0.30±0.03 at 10− molal concentration in fair agreement with earlier data.

Kinetics and mechanism of complex formation between 1-(2-hydroxyphenyl)-3,5-diphenylformazan and ammineaquonickel(II) complexes

Abstract A kinetic study is reported on the reaction between nickel(II) perchlorate and the tridentate ligand 1-(2-hydroxyphenyl)-3,5-diphenylformazan, resulting in two linkage isomers, in ammonia ammonium perchlorate buffers in an ethanolwater (50 wt.%) mixture. The medium dependence of the rate law and the isomer product ratio were analysed on the basis of the Eigen-Wilkins mechanism. The first step of the two-ring chelate coordination seems to be the formation of the Ni(II)-phenoxide bond, followed by a rate-determining Ni(II)N ring closure. The isomer rearrangement reaction gave information on the decomposition of the complex. The pH dependence of the rate of decomposition indicates the closure of the first ring to be rate-determining

Solvent dependence of the stereochemistry of base-catalyzed solvolysis of trans-[Co(NH3)4(15NH3)X]3+/2+(X = Me2SO or Cl) ions

The cis–trans product ratio for the base-catalyzed solvolysis of the 15NH3 labelled trans-[Co(NH3)4(15NH3)Cl]2+ ion has been determined as a function of the solvent. The solvents used were H2O–CH3OH and H2O–dmso (dimethyl sulphoxide) mixtures, as well as anhydrous CH3OH and CH3NH2. The trans-[Co(NH3)4(15NH3)(dmso)]3+ ion was included also in the study. The base hydrolysis results do not show any solvent or leaving-group dependence, within experimental error (2%). All trans systems give (44 ± 1)% rearrangement. Small, significant differences are shown by the penta-amminechloro-complex in CH3NH2(50% rearrangement) and by the dmso complex (48% rearrangement in H2O and 46% in CH3OH). The results are interpreted as indicating the adequacy of a mechanistic model involving a five-co-ordinate intermediate.