Thermodynamics of Alkali−Metal Cations and Macrocycles (18-Crown-6, Ethyl p-tert-butylcalix(6)arenehexanoate, Cryptand 222) in Solution and in the Solid State

Abstract

Stability constants and derived Gibbs energies and enthalpies and entropies of complexation of alkali−metal cations and macrocycles (18-crown-6 and ethyl p-tert-butylcalix(6)arenehexanoate) in benzonitrile at 298.15 K derived from titration calorimetry (macro and micro) are first reported. These data are compared with those previously reported for cryptand 222 and these cations in this solvent. A “peak” selectivity is observed for the complexation of the calix(6)arene ester and alkali metal cations with a monotonic increase in stability from lithium to potassium followed by a decrease from the latter to rubidium. This behavior is analogous to that shown for cation binding involving 18-crown-6 and cryptand 222. Similar to the process of complex formation involving these ligands, that involving the calix(6)arene ester and these metal cations is enthalpy controlled with an exothermic maximum for the potassium cation. Among the ligands considered, thermodynamic data involving cation−calix(6)arene ester interactions are characterized by a lower enthalpic stability (less exothermic) and a more favorable entropy (except for K+) than corresponding data involving cryptand 222 or indeed 18-crown-6. These results are analysed in terms of solute−solvent interactions reflected on the solution thermodynamic data of the free and the complexed electrolytes and the ligand in benzonitrile. Standard enthalpies of solution of macrocycles and their sodium and potassium salts in benzonitrile measured calorimetrically are discussed in relation to (i) corresponding data for the uncomplexed salts and (ii) previously reported data for sodium and potassium cryptate salts in various solvents. Enthalpies of coordination referred to the process in the solid state for eighteen systems involving sodium and potassium coronates, cryptates, and calix(6)arenates are derived and whenever possible these are discussed on the basis of (i) available X-ray crystallographic data and (ii) the anion effect on the coordination process.

Thermodynamics of cation (alkali-metal) complexation by 5,11,17,23-tetra-tert-butyl[25,26,27,28-tetrakis(2-pyridylmethyl)oxy]- calix(4)arene and the crystal structure–superstructure of its 1:1 complex with sodium and acetonitrile

“…( 5 systems involving 1a with the cation and solvent although these are less pronounced than the corresponding data for systems involving these cations and calix(4)-and calix(6)arene esters in these solvents. 43 The changes observed in values are likely to be attributed to the di †erences in * cf S¡ solvation of the ligand relative to the metal-ion complex in these solvents and these should be further investigated.…”

Substituent effects on the stabilities of polymeric and small molecule bis-terpyridine complexes

“…The resulting light brown tacky solid was determined to be suitably pure by NMR and used without further purification. 1 Poly(ethylene oxide) functionalized with 4 0 -(N-2-hydroxyethyl-N-methylamino)-2,2 0 :6 0 ,2 00 -terpyridine (7). An oven-dried 50 mL round-bottomed flask was charged with 0.095 g of 4 0 -(N-2hydroxyethyl-N-methylamino)-2,2 0 :6 0 ,2 00 -terpyridine, 0.0075 g of sodium hydride and an egg-shaped stir bar and fitted with a septum.…”

“…The purple solution was stirred for 30 min, and the product was recrystallized from the reaction mixture, giving granular red crystals. Yield: 0.0233 g (37.0%) 1 Preparation of complexes of (7) with iron and cobalt. Complexes of (7) were prepared using the same technique as those used for (4a), except that the cobalt complexes were left in air for at least 1 d to ensure complete oxidation of cobalt(II) to cobalt(III).…”

“…[1][2][3][4] It is well established that variations in the metal used to form complexes with these ligands yield changes by many orders of magnitude in both the kinetic rate constants for formation and dissociation of complexes 5,6 and the thermodynamic binding constants. 7 These effects are critical to informing the metalligand combination selected, as they determine the properties of the resulting supramolecular structures. [8][9][10] Another potentially important, although infrequently considered, factor is that the synthetic pathway used to attach the ligands to the building blocks necessarily introduces substituent groups, which may influence ligand behavior.…”

Solution thermodynamics of Lanthanide–Cryptand 222 complexation processes

“…Thermodynamic data for the complexation of silver and cryptand 222 in acetonitrile at 298.15 K, i.e., are well established [33]. Combination of Eqs.…”