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

Abstract

The interaction of 5,11,17,23-tetra-tert-butyl [25,26,27,28-tetrakis(2-pyridylmethyl)oxy]calix(4)arene 1a with alkali-metal cations in dipolar aprotic media (acetonitrile and benzonitrile) has been investigated. 1H NMR experiments were carried out by adding to the ligand an excess amount of the appropriate metal cation (Li`, Na`, K`) in at 298 K. Measurements were taken at di †erent time intervals ranging from 30 min to 10 CD 3 CN days. It was found that the kinetics of the process in this solvent is fast. Conductance measurements demonstrated that 1 : 1 metal cation : ligand stoichiometries are found with these cations in these solvents. Thermodynamic parameters of complexation for this ligand and alkali-metal cations in acetonitrile and in benzonitrile at 298.15 K were derived from titration microcalorimetry. Stability constants were also determined by the competitive potentiometric method using silver electrodes. Excellent agreement is found between the data derived from calorimetry and those derived by potentiometry. The highest stability is found for lithium with this ligand. The results are compared with data previously reported for systems involving a calix(4)arene ester derivative and these cations in the same solvents. The implications of stability constant data on the selective behaviour of this ligand for metal cations in these solvents are discussed. It is shown that this ligand in these solvents is able to discriminate between the smaller cations (Li`and Na`) and the larger ones (K`and Rb`). The sodium perchlorate complex of 1a was synthesised and the molecular structure of this complex has been determined from X-ray di †raction data. The substance crystallises in the tetragonal group P4cc with a \ 21.791(2), c \ 26.958(3) and z \ 8. There are three di †erent complexes in the lattice, two sited Ó on fourfold axes and a third one on a twofold axis. All ligands exhibit a " cone Ï conformation and the Na`ion is encapsulated in their hydrophilic pockets with an acetonitrile molecule Ðlling their hydrophobic cavities. Based on 1H NMR, conductimetric, microcalorimetric and X-ray di †raction studies Ðnal conclusions are given.

Binding properties of p-tert-butyldihomooxacalix[4]arene tetra(2-pyridylmethoxy) derivative towards alkali, alkaline earth, transition and heavy metal cations

“…The oxygen bridge equatorial and axial methylene protons (CH 2 OCH 2 ) and the bridging axial methylene protons (ArCH 2 Ar) show the largest upfield shifts. Similar observations have been made for related pyridino-calixarenes, 8,10,[17][18][19]30 as well as for other dihomooxa derivatives. 22,31 A closer examination of the spectral changes upon complexation indicates very small variations (Dd E 0.05 ppm) for the tert-butyl groups.…”

“…Our results for K + and Ag + with the latter ligand are in full agreement with the values determined previously by other authors. 8,9 The stability constant of the potassium complex with dihomooxa ligand 2 derived from the microcalorimetric measurements is in full agreement with the value obtained from spectrophotometry. The results show that the enthalpy and the entropy of complexation are responsible for the stabilisation of this complex, both contributions being of the same order of magnitude.…”

“…In acetonitrile, the stability constants of the alkali metal complexes were already published. 8 They were obtained by techniques other than the one used in this work, namely microcalorimetry (log b = 5.36 and 3.10 for Na + and K + , respectively) and competitive potentiometry (log b = 5.61 and 3.17 for Na + and K + , respectively). Our values for sodium and potassium complexes derived from spectrophotometric determinations (Table 1) are quite consistent with these previous data.…”

“…In particular, the functionalisation of calix[n]arenes with 2pyridylmethyl pendant groups at the lower rim has been performed. 6 Thus, pyridino-calix[4]-, 7-12 -[5]-, 13 -[6]- [14][15][16] and - [8]arene 16 derivatives, as well as, pyridino-homo- 17,18 and -homooxacalixarene 19,20 derivatives have been obtained.…”

Lower rim calix(4)arene ketone derivatives and their interaction with alkali metal cations. Structural and thermodynamic (solution and complexation) characterisation of the tetraphenyl ketone derivative and its sodium complex

“…solutions was left for 30 min to equilibrate and after that a solution of sodium perchlorate 41) ÈNaÈO(11) 79.81( 13) O( 41)ÈNaÈO (32) 77.85( 14) O( 11)ÈNaÈO (32) 150.86( 13) O( 41)ÈNaÈO (31) 85.38( 12) O( 11)ÈNaÈO (31) 130.95( 17) O( 32)ÈNaÈO (31) 65.38( 13) O( 41)ÈNaÈO (22) 149.55( 15) O(11)ÈNaÈO (22) 130.33( 13) O( 32)ÈNaÈO (22) 72.30( 14) O( 31)ÈNaÈO (22) 76.98( 14) O( 41)ÈNaÈO (21) 133.64( 16) O( 11)ÈNaÈO (21) 82.80( 12) O( 32)ÈNaÈO (21) 126.30( 14) O( 31)ÈNaÈO (21) 74.46(10) O( 22)ÈNaÈO (21) 64.87( 15) O( 41)ÈNaÈO (12) 127.66( 13) O( 11)ÈNaÈO (12) 63.81( 15) O( 32)ÈNaÈO (12) 117.89( 18) O( 31)ÈNaÈO…”