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Molecular Switch Triggered by Solvent Polarity: Synthesis, Acid–Base Behavior, Alkali Metal Ion Complexation, and Crystal Structure
Author(s) -
Ambrosi Gianluca,
Dapporto Paolo,
Formica Mauro,
Fusi Vieri,
Giorgi Luca,
Guerri Annalisa,
Micheloni Mauro,
Paoli Paola,
Pontellini Roberto,
Rossi Patrizia
Publication year - 2003
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200390090
Subject(s) - alkali metal , chemistry , potentiometric titration , solvent , polarity (international relations) , metal , ion , metal ions in aqueous solution , base (topology) , inorganic chemistry , moiety , ligand (biochemistry) , crystallography , solvent polarity , stereochemistry , organic chemistry , mathematical analysis , biochemistry , receptor , mathematics , cell
The synthesis and characterization of the new tetraazamacrocycle L, bearing two 1,1′‐bis(2‐phenol) groups as side‐arms, is reported. The basicity behavior and the binding properties of L toward alkali metal ions were determined by means of potentiometric measurements in ethanol/water 50:50 (v/v) solution (298.1±0.1 K, I =0.15 mol dm −3 ). The anionic H −1 L − species can be obtained in strong alkaline solution, indicating that not all of the acidic protons of L can be removed under the experimental conditions used. This species behaves as a tetraprotic base (log K 1 =11.22, log K 2 =9.45, log K 3 =7.07, log K 4 =5.08), and binds alkali metal ions to form neutral [MH −1 L] complexes with the following stability constants: log K Li =3.92, log K Na =3.54, log K K =3.29, log K Cs =3.53. The arrangement of the acidic protons in the H −1 L − species depends on the polarity of the solvents used, and at least one proton switches from the amine moiety to the aromatic part upon decreasing the polarity of the solvent. In this way two different binding areas, modulated by the polarity of solvents, are possible in L. One area is preferred by alkali metal ions in polar solvents, the second one is preferred in solvents with low polarity. Thus, the metal ion can switch from one location to the other in the ligand, modulated by the polarity of the environment. A strong hydrogen‐bonding network should preorganize the ligand for coordination, as confirmed by MD simulations. The crystal structure of the [Na(H −1 L)]⋅CH 3 CN complex (space group P 2 1 / c, a =12.805(1), b =20.205(3), c =14.170(2) Å, β =100.77(1)°, V =3601.6(8) Å 3 , Z =4, R =0.0430, wR 2=0.1181), obtained using CH 2 Cl 2 /CH 3 CN as mixed solvent, supports this last aspect and shows one of the proposed binding areas.