Kinetics and mechanism of the acid-catalysed hydrolysis of the carbonatotetraimidazolecobalt(III) ion

Summary The kinetics of the acid-catalysed hydrolysis of the [(imidazole)₄Co(CO₃)]⁺ ion was found to follow the rate law -dln[complex]/dt = k ₁ K[H⁺](1 + K[H ⁺]) in the 25–45 °C range, [H⁺] 0.05–1.0 m range and I = 1.0m. The reaction sequence consists of a rapid protonation equilibrium followed by the one-end dissociation of the coordinated carbonato ligand (rate-determining step) and subsequent fast release of the monodentate carbonato ligand. The rate parameter values, k ₁ and ITK, at 25 °C are 6.48 × 10⁻³s⁻¹ and 0.31m ⁻¹, respectively, and activation parameters for k ₁ are ΔH ₁ ^≠ = 86.1 ± 1.2kJ mol⁻¹ and ΔS ₁ ^≠ = 2.1 ± 6.3 J mol⁻¹K⁻¹. The hydrolysis rate increases with increase in ionic strength. The different ways of dealing with the data fit are presented and discussed. The kinetic results are compared with those for the similar cobalt(III) complexes.     

Decomposition of oxalate by hydrogen peroxide in aqueous solution

The decomposition rate of oxalate by hydrogen peroxide has been investigated by a KMnO₄ titration method. The rate equation for decomposition of hydrogen peroxide in the aqueous phase is 1n([H₂O₂]/[H₂O₂]₀)=?k₁·t, where k₁=0.2, for [H⁺]<2M, k₁=0.2+0.34([H⁺]?2), for [H⁺]>2M. As the acidity increases over 2M, an acid catalysis effect appeard. The new rate equation proposed for the decomposition of oxalate by hydrogen peroxide is $$ - \frac{d}{{dt}}X_{[OX]} = k_2 [H_2 O_2 ]_0 (1 - X_{[OX]} )(e^{ - k_1 t} - \frac{{[OX]_0 }}{{[H_2 O_2 ]_0 }}X_{[OX]} )$$ The rate constant for decomposition of oxalate, k₂, increased with nitric acid concentration and the effect of hydrogen ion concentration was expressed as k₂=a[H⁺]ⁿ, where the values fora andn were a=1.54, n=0.3 at [H⁺]<2M, a=0.31, n=2.5 at [H⁺]>2M, respectively.     

Kinetics and Mechanism of Chromium(III)-Picolinato and Chromium(III)-Dipicolinato Complexes Aquation in HNO3 Solutions

The acid-catalyzed aquation of [Cr(pic)(H₂O)₄]₂ ²⁺ and [Cr(dpic)(H₂O)₃]⁺(pic = picolinic acid anion, dpic = dipicolinic acid dianion) in nitrate(V) media was studied. The reaction is reversible in the case of the pic-complex and practically irreversible in the case of the dpic-complex. It is assumed that the reactive form of the substrate undergoes fast chelate ring-opening followed by protolytic equilibria, followed by the rate of the Cr—O bond breaking of the monodentate bonded ligand which is the rate-determining step. The kinetics of pic/dpic ligand liberation were followed spectrophotometrically in the 0.4–2.0 M HNO₃ range at I= 2.0 M. The following dependences of the pseudo-first order rate constants on [H⁺] have been established:k _obs=a+b[H⁺](where b and a are apparent rate constants for the forward and the reverse reaction of the pic-complex) and k _obs=b[H⁺]+c[H⁺]²(where b and c are apparent rate constants for the dpic liberation). Fast protolytic pre-equilibria, leading to protonation of the carboxylic oxygen atom on the monodentate bonded ligand, preceeds ligand liberation.     

Kinetics and mechanism of the first aquation stage for the [Cr(pic)3]0 and [Cr(pic)2(OH)]2 0 complexes in HClO4 solutions

Aquation of [Cr(pic)₃]⁰ and [Cr(pic)₂(OH)]₂ ⁰ in aqueous HClO₄ solutions leads to formation of the common product – [Cr(pic)₂(H₂O)₂]⁺. The first, reversible stage, the ring opening via Cr—N bond breaking in [Cr(pic)₃]⁰ is followed by the second, rate-determining step – one-end bonded pic ligand liberation. In the case of the [Cr(pic)₂(OH)]₂ ⁰ complex, the first faster stage produces the singly bridged dimer, which undergoes cleavage into the parent monomers in the second, much slower step. The subsequent aquation of [Cr(pic)₂(H₂O)₂]⁺ is extremely slow and leads to [Cr(pic)(H₂O)₄]²⁺ formation, which practically does not undergo further ligand substitution under the conditions applied. Kinetics of the first aquation stage for [Cr(pic)₃]⁰ and of the second step for [Cr(pic)₂(OH)]₂ ⁰ were studied spectrophotometrically in the 0.1–1.0 M HClO₄ range at I = 1.0 M. The observed pseudo-first order rate constant for [Cr(pic)₃]⁰ decreases with [H⁺] increase according to the rate law: k _obs = k ₁ + k _–1 Q ₁/[H⁺], where k ₁ and k _–1 are the rate constants of the forward and the reverse processes in the unprotonated substrate and Q ₁ is the protonation constant of the pyridine nitrogen atom. In the case of the [Cr(pic)₂(OH)]₂ ⁰ complex, the rate for the singly bridged dimer cleavage does not depend on [H⁺]. The activation parameters for the chelate-ring opening in [Cr(pic)₃]⁰ and for the singly bridged dimer cleavage have been determined and discussed. Some kinetic data of the slow, second aquation stage for the [Cr(pic)₃]⁰ complex and of the fast, first aquation stage for the doubly bridged dimer have been studied; for both reactions the rate increases linearly with the increase in [H⁺].     

Dinuclear complexes with a μ-cyano ligand. Part XI(1). Synthesis and characterization of several derivatives ofcis-[Co(NH3)(en)2(H2O)]3+

Summary The new complex double saltscw-[Co(NH₃)(en)₂(H₂O)]₂ [M(CN)₄]₃ (en = ethylenediamine; M = Ni, Pd or Pt),cis-[Co(NH₃(en)₂(H₂O)]₂[FeNO(CN)₅]₃ andcis-[Co(NH₃)(en)₂(H₂O)][Co(CN)₆] have been synthesized and by anation in the solid state the corresponding new dinuclear complexes with a cyano bridgecis- ortrans-[(NH₃)(en)₂Co-NC-M(CN)₃]₂ [M(CN)₄] (M = Ni, Pd or Pt);cis-, trans-[(NH₃)(en)₂Co-NC-FeNO(CN)₄]₂[FeNO(CN)₅] andcis-[(NH₃)(en)₂Co-NC-Co(CN)₅ have been prepared. The complexes have been characterized by chemical analysis, t.g. measurements, and by i.r. and electronic spectroscopy. With [Ni(CN)₄][^2– and [Co(CN)in]₆ ^3– only thecis-isomer is produced; with [Pd(CN)₄]^2–, [Pt(CN)₄]^2– and [FeNO(CN)₅]^2– thetrans- isomer is the dominant species. The dinuclear complex derived from [Pt(CN)₄]^2– shows strong Pt-Pt interactions both in the solid state and in solution.     

Darstellung,Kristallstruktur, thermischer Abbau und Schwingungsspektren von [Co(NH3)6]2[Be4O(CO3)6] · 10 H2O

Preparation, Crystal Structure, Thermal Decomposition, and Vibrational Spectra of [Co(NH₃)₆]₂[Be₄O(CO₃)₆] · 10 H₂O [Co(NH₃)₆]₂[Be₄O(CO₃)₆] · 10 H₂O is a suitable compound for the quantitative determination of beryllium. It can be obtained by reaction of aqueous solutions of carbonatoberyllate with [Co(NH₃)₆]Cl₃. The crystal structure (trigonal‐rhombohedral, R3c (Nr. 161), a = 1071,6(1) pm, c = 5549,4(9) pm, V_EZ = 5519(1) · 10⁶ pm³, Z = 6, R1(I ≥ 2σ(I)) = 0,037, wR2(I ≥ 2σ(I)) = 0,094) contains [Co(NH₃)₆]³⁺‐ and [Be₄O(CO₃)₆]^6–‐ions, which are directly hydrogen bonded as well as with water molecules. The complex cations and anions occupy the positions of a distorted anti‐CaF₂‐type. The thermal decomposition, IR and Raman spectra are presented and discussed.     

Chromium(III) complexes with lutidinic acid: kinetic studies in HClO<Subscript>4</Subscript> and NaOH solutions

Chromium(III)-lutidinato complexes of general formula [Cr(lutH) _n (H₂O)_6−2n ]³⁻ⁿ (where lutH⁻ is N,O-bonded lutidinic acid anion) were obtained and characterized in solution. Acid-catalysed aquation of [Cr(lutH)₃]⁰ leads to only one ligand dissociation, whereas base hydrolysis produces chromates(III) as a result of subsequent ligand liberation steps. The kinetics of the first ligand dissociation were studied spectrophotometrically, within the 0.1–1.0 M HClO₄ and 0.4–1.0 M NaOH range. In acidic media, two reaction stages, the chelate-ring opening and the ligand dissociation, were characterized. The dependencies of pseudo-first-order rate constants on [H⁺] are as follows: k _obs1 = k ₁ + k ₋₁/K ₁[H⁺] and k _obs2 = k ₂ K ₂[H⁺]/(1 + K ₂[H⁺]), where k ₁ and k ₂ are the rate constants for the chelate-ring opening and the ligand dissociation, respectively, k ₋₁ is the rate constant for the chelate-ring closure, and K ₁ and K ₂ are the protonation constants of the pyridine nitrogen atom and coordinated 2-carboxylate group in the one-end bonded intermediate, respectively. In alkaline media, the rate constant for the first ligand dissociation depends on [OH⁻]: k _obs1 = k _OH(1) + k _O[OH⁻], where k _OH(1) and k _O are rate constants of the first ligand liberation from the hydroxo- and oxo-forms of the intermediate, respectively, and K ₂ is an equilibrium constant between these two protolytic forms. Kinetic parameters were determined and a mechanism for the first ligand dissociation is proposed. The kinetics of the ligand liberation from [Cr(lut)(OH)₄]³⁻ were also studied and the values of the pseudo-first-order rate constants are [OH⁻] independent.     

Ion–molecule reaction in the gas phase 3—nucleophilic substitution of 17ξ-R-5α,14β-androstane-14,17ξ-diols under [NH4]+ chemical ionization conditions1

Under Ammonia chemical Ionization conditions the source decompositions of [M + NH₄]⁺ ions formed from epimeric tertiary steroid alchols 14 OH_β, 17OH_α or 17 OH_β substituted at position 17 have been studied. They give rise to formation of [M + NH₄? H₂O]⁺ dentoed as [MH_sH]⁺, [M_sH? H₂O]⁺, [M_sH? NH₃]⁺ and [M_sH? NH₃? H₂O]⁺ ions. Stereochemical effects are observed in the ratios [M_sH? H₂O]⁺/[M_sH? NH₃]⁺. These effects are significant among metastable ions. In particular, only the [M_sH]⁺ ions produced from trans-diol isomers lose a water molecule. The favoured loss of water can be accounted for by an S_N2 mechanism in which the insertion of NH₃ gives [M_sH]⁺ with Walden inversion occurring during the ion-molecule reaction between [M + NH₄]⁺ + NH₃. The S_N1 and S_Ni pathways have been rejected.     

Studies on the exchange characteristics of [Co(NH3)6]3+ in amberlite IRC-50

Summary The exchange of Co(NH₃)₆]³⁺-ions on amberlite IRC-50 resin has been studied at room temperature. For this exchange process the cations are effective in the order: Cs⁺<Rb⁺<K⁺<Na⁺<Li⁺<NH₄ ⁺<Mg²⁺ <Ca²⁺<H⁺ and (C₂H₅)₄N<(CH₃)₄N⁺ ≪Cetyltrimethylammonium-ion <Cetylpyridinium-ion. The logarithm of the selectivity coefficient gives linear graphs when plotted against the radius of the hydrated ions or the reciprocals of theDebye-Hückel parameter?.     

Kinetics and mechanism of the reaction between dimethylformamide and chromium(VI)

The kinetics of oxidation of N,N‐dimethylformamide by chromium(VI) has been studied spectrophotometrically in aqueous perchloric acid media at 20°C. The rate showed a first‐order dependence on both [Cr(VI)] and [DMF], and increased markedly with increasing [H⁺]. The order with respect to [HClO₄] was found to lie between 1 and 2. The rate was found to be independent of ionic strength as well as of any inhibition effect of Mn(II). The formation of superoxochromium(III) ion was detected in an aerated solution of chromium(VI), DMF and HClO₄. The proposed mechanism, involving two reaction pathways, leads to the rate law, rate = K_a1 [HCrO₄⁻] [DMF] (k_I K_a2 [H⁺]²+k_II[H⁺]). The first pathway, with rate constant k_I, involves the formation of chromium(V) and a free radical. The second pathway, with rate constant k_II, involves the formation of Cr(IV), CO₂ and dimethylamine. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 409–415, 1999     

Zur Kenntnis der Sulfito-kobalt(III)-Ammine. III. Hydrogensulfitokobalt(III)-Ammine

Sulphito Cobalt(III) Ammines. III. Hydrogensulphito Cobalt(III) Ammines Concentrated acids react with [CoSO₃(NH₃)₅]⁺ salts hydrogen- sulphitopentaamminecobalt(III) complexes. [Co(HSO₃)(NH₃)₅]Cl₂, [Co(HSO₃)(NH₃)₅]Br₂ and [Co(HSO₃)(NH₃)₅](HSO₄)₂·H₂O have been isolated. These substances are yellow coloured in contrast to an earlier work which reported red colour. Furthermore, the hydrogensulphitoacidotetreaammine complexes [Co(HSO₃)Cl(NH₃)₄]Cl, [Co(HSO₃)Cl(NH₃)₄]ClO₄·H₂O, [Co(HSO₃)Br(NH₃)₄]Br and [Co(HSO₃) CN(NH₃)₄]Cl habe been prepared. [Co(HSO₃)Br(NH₃)₄]Br is losing spontaneously HBr forming [CoSO₃Br(NH₃)₄]. The neutral complex [Co(HSO₃)SO₃(NH₃)₄]·1/2H₂O has been obtained from cis- NH₄[Co(SO₃)₂(NH₃)₄] and HCl. The absorption spectra in the IR, visible and UV region are reported and discussed. The HSO₃ group is coordinated to Co through the S atom. The Co? S bond is weaker than in the sulphito complexes as concluded from the RAMAN spectrum. In the new complexes, the hydrogensulphito ligand causes a minor trans effect than the sulphito ligand.     

The production of Cr(NH3)6 from the acid catalysed hydrolysis of Cr(NH3)5(NCO)

The rate of the reaction

has been investigated at 40–65°C with [HClO₄] varying from 0.04 to 0.6 M (μ = 0.6 M, NaClO₄). The observed rate law has the form: -d[Cr(NH₃)₅(NCO)²⁺]/dt = k_obs[Cr(NH₃)₅(NCO)²⁺] where k_obs = a[H+]²{1 + b[H⁺]²} and ^?1 at 55.0°C, a = 0.36 M^?1 s^?2 and b = 6.9 × 10^?3 M^?1 s^?1. The rate of loss of Cr(NH₃)₅(NCO)²⁺ increases with increasing acidity to a limiting value (at [H⁺] ～ 0.5 M) but the yield of Cr(NH₃)₆³⁺ decreases with increasing [H⁺] and increases with increasing temperature. In the kinetic studies the maximum yield of Cr(NH₃)₆³⁺ was 35% but a synthetic procedure has been developed to give a 60% yield.     

Two New Silver(I) Ammine Complexes by Displacement Reaction Between [Ag(NH3)2]+ Ions and Different Pyridine‐4,5‐Imidazoledicarboxylic Acids

[Ag(NH₃)₂]⁺ ions are chosen as an initial reaction precursor because of its simple displacement reaction and intrinsic arrangement as well as specific coordination directionality. Two new silver(I) ammine complexes, Ag₂(NH₃)HL² ( 2 ) and Ag₂(NH₃)₂HL³ ( 3 ), were obtained by a simple substitution reaction between [Ag(NH₃)₂]⁺ ions and pyridine‐4,5‐imidazoledicarboxylic acid [H₃L² = 2‐(3′‐pyridyl) 4,5‐imidazoledicarboxylic acid and H₃L³ = 2‐(4′‐pyridyl) 4,5‐imidazoledicarboxylic acid]. Silver dimers are connected into a 2D layer and 1D chain in complexes 2 and 3 , respectively. In complex 2 two kinds of displacement reactions (mono‐substituting and bis‐substituting) occurred between the ammine molecules in [Ag(NH₃)₂]⁺ ions and H₃L², however, only the mono‐substituting reaction occurs in complex 3 .     

Controlled Aggregation of Multiple Guanidinium Ions through a Hydrogen‐Bonded Network Assembly with Deprotonated Forms of Kemp’s Triacid

A series of five complexes that incorporate the guanidinium ion and various deprotonated forms of Kemp’s triacid (H₃KTA) have been synthesized and characterized by single‐crystal X‐ray analysis. The complex [C(NH₂)₃⁺] ? [H₂KTA^?] ( 1 ) exhibits a sinusoidal layer structure with a centrosymmetric pseudo‐rosette motif composed of two ion pairs. The fully deprotonated Kemp’s triacid moiety in 3 [C(NH₂)₃⁺] ? [KTA^3?] ( 2 ) forms a record number of eighteen acceptor hydrogen bonds, thus leading to a closely knit three‐dimensional network. The KTA^3? anion adopts an uncommon twist conformation in [(CH₃)₄N⁺] ? 2 [C(NH₂)₃⁺] ? [KTA^3?] ? 2 H₂O ( 3 ). The crystal structure of [(nC₃H₇)₄N⁺] ? 2 [C(NH₂)₃⁺] ? [KTA^3?] ( 4 ) features a tetrahedral aggregate of four guanidinium ions stabilized by an outer shell that comprises six equatorial carboxylate groups that belong to separate [KTA^3?] anions. In 3 [(C₂H₅)₄N⁺] ? 20 [C(NH₂)₃⁺] ? 11 [HKTA^2?] ? [H₂KTA^?] ? 17 H₂O ( 5 ), an even larger centrosymmetric inner core composed of eight guanidinium ions and six bridging water molecules is enclosed by a crust composed of eighteen axial carboxyl/carboxylate groups from six HKTA^2? anions.     

Kinetics and Mechanism of Chromium(III)-oxalates-2-hydroxynicotinate and Chromium(III)-oxalates-3-hydroxypicolinate Aquation in HClO4 Solutions

New chromium(III) complexes, [Cr(C₂O₄)₂(2-hnic)]²⁻ and [Cr(C₂O₄)₂(3-hpic)]²⁻ (where 2-hnic = O,O′-bonded 2-hydroxynicotinic acid and 3-hpic = N,O-bonded 3-hydroxypicolinic acid), were obtained and characterized in solution. The acid-catalyzed aquation of the both complexes leads to liberation of the appropriate pyridinecarboxylic acid and formation of cis-[Cr(C₂O₄)₂(H₂O)₂]⁻. Kinetics of these reactions were studied spectrophotometrically in the 0.1–1.0 M HClO₄ range, at I = 1.0 M. In the case of [Cr(C₂O₄)₂(2-hnic)]²⁻, a slow chelate-ring opening at the Cr–O (phenolate) bond is followed by a fast Cr–O (carboxylate) bond breaking. The rate law: k_obs = k_HQ_H[H⁺] was established, where k_H is the acid-catalyzed rate constant and Q_H is the protonation constant of the coordinated phenolate oxygen atom. In the case of [Cr(C₂O₄)₂(3-hpic)]²⁻, the reversible chelate-ring opening at Cr–N bond is followed by the rate determining step – the one-end bonded ligand liberation. The rate law for the first step was determined: k_obs = k₁+k₋₁/Q₁[H⁺], where k₁ and k₋₁ are the rate constants of the chelate-ring opening and closure and Q₁ is the protonation constant of the pyridine nitrogen atom. The aquation mechanisms are proposed and the effect of ligand coordination mode on complex reactivity is discussed.     

Acid-catalyzed Hydrolysis of the cis-[Cr(1,10-phenanthroline)2(O2CO)]+ Ion Studied by the u.v.–vis Stopped Flow Method

The cis-[Cr(phen)₂(O₂CO)]⁺ ion was prepared through the displacement of two molecules of water from the cis-[Cr(phen)₂(OH₂)₂]³⁺ by the bidentate carbonate anion. It underwent two-phase hydrolysis reactions under acidic conditions (0.1 < [H⁺] < 2.7 m) at 5, 10, 15, 20 and 25 °C. Via slow carbonato chelate ring opening (first step k₁^slow) and a second fast decarboxylation(k₂^fast value). The first step was preceded by protonation of the coordinate bidentate carbonate ligand. The second step exhibited no pH dependence, while k₁^slow values increased with acid concentration that suggested the presence of both protonated and deprotonated reactant species. Based on these observations we have proposed a hydrolysis mechanism featuring H₂O-induced ring-opening of the coordinate CO₃²⁻ group in the first step k₁^slow followed by loss of CO₃²⁻ from two intermediates, [Cr(phen)₂(O₂COH)]²⁺ (k₁^slow) and [Cr(phen)₂(OH₂)(O₂COH)]²⁺ (k₂^fast).     

Inner-sphere oxidation of iron(II) by tris(malonato)cobaltate(III)

The kinetics of oxidation of Fe²⁺ by [Co(C₃H₂O₄)₃]^3? in acidic solutions at 605 nm showed a simple first-order dependence in each reactant concentration. The second-order rate constant dependence on [H⁺] is in accordance with eqn (i) k₂ = k′₂ + k₃[H⁺] (i) where k′₂ and k₃ have values of 73.4 ± 14.0 M ^?1 s^?1 and 353 ± 41 M^?2 s^?1, respectively, at 1.0 M ionic strength (NaClO₄) and 25°C. At 310 nm the formation and decomposition of an intermediate, believed to be [FeC₃H₂O₄]⁺, was observed. The increase in the rate of oxidation with increasing [H⁺] was interpreted in terms of a “one-ended” dissociation mechanism which facilitates chelation of Fe₂₊ by the carbonyl oxygens of malonate in the transition state.     

Electron Transfer in Metal‐Organic Molecules. A Time Resolved EXAFS and Optical Spectroscopy Study

We have measured, by means of ultrafast x‐ray absorption and optical spectroscopy, the M‐O (M=Fe, Co) and Co‐N metal to ligand bond length change as a function of time and the formation and decay of the excited states and intermediate species, after excitation with a 267 nm femtosecond pulse. These experimental data combined with DFT calculations allowed us to determine the mechanism of electron transfer operating in the redox reaction of two metal‐ligand complexes, [M(III)(C₂O₄)₃]^3‐ and [Co(III)(NH₃)₆ ]³⁺. Based on the data we find that, even though both molecules are excited into their charge transfer band, the redox reaction of [M(III)(C₂O₄)₃]^3‐ proceeds via intermolecular electron transfer while [Co(III)(NH₃)₆ ]³⁺ electron transfer mechanism is intramolecular.     

The Protonation of Acetamide and Thioacetamide in Super­acidic Solutions: Crystal Structures of [H3CC(OH)NH2]+AsF6– and [H3CC(SH)NH2]+AsF6–

Acetamide and thioacetamide react with the superacid solutions HF/MF₅ (M = As, Sb) under formation of the corresponding salts [H₃CC(OH)NH₂]⁺MF₆^– and [H₃CC(SH)NH₂]⁺MF₆^– (M = As, Sb), respectively. The reaction of DF/AsF₅ with acetamide and thioacetamide lead to the corresponding deuterated salts [H₃CC(OD)ND₂]⁺AsF₆^– and [H₃CC(SD)ND₂]⁺AsF₆^–, respectively_. The salts are characterized by vibrational and NMR spectroscopy, and in the case of [H₃CC(OH)NH₂]⁺AsF₆^– and [H₃CC(SH)NH₂]⁺AsF₆^– also by single‐crystal X‐ray analyses. The [H₃CC(OH)NH₂]⁺AsF₆^– ( 1 ) salt crystallizes in the triclinic space group P$\bar{1}$ with two formula units per unit cell, and the [H₃CC(SH)NH₂]⁺AsF₆^– ( 2 ) salt crystallizes in the monoclinic space group P2₁/c with four formula units per unit cell. In both crystal structures three‐dimensional networks are observed which are formed by intra‐ and intermolecular N–H ··· F and O–H ··· F or S–H ··· F hydrogen bonds, respectively. For the vibrational analyses, quantum chemically calculated spectra of the cations [H₃CC(OH)NH₂ · 3HF]⁺ and [H₃CC(SH)NH₂ · 2HF]⁺ are considered.     

Second‐sphere coordination in anion binding: sodium hexa­ammine­cobalt(III) tetra­kis­(4‐fluoro­benzoate) monohydrate

In sodium hexa­amminecobalt(III) tetra­kis­(4‐fluoro­benzoate) monohydrate, Na[Co(NH₃)₆](C₇H₄FO₂)₄·H₂O, determined at 180 K, [Co(NH₃)₆]³⁺ cations lie on centres of inversion and form layers in which their C₄ axes lie perpendicular to the layer planes. 4‐Fluoro­benzoate anions lie on twofold axes and general positions and adopt near‐planar geometries. Na⁺ cations and water mol­ecules lie on twofold axes, forming [NaO₅] square pyramids that lie between the [Co(NH₃)₆]³⁺ cations. The second‐sphere inter­actions between [Co(NH₃)₆]³⁺ cations and 4‐fluorobenzoate anions comprise edge‐to‐face and vertex‐to‐face arrangements. The structure is closely comparable with that of the benzoic acid salt, demonstrating that fluorination of the anion in the para position has no significant influence on the second‐sphere inter­actions and minimal influence on the gross crystal structure.