| Abstract
| - Complexation behavior of a previously described heteroditopic cryptand L1 and a newly synthesized cryptand L2toward transition metal ions is described. The cryptands readily accept a transition metal ion like Cu(II) or Ni(II)at the N4 end of the cavity forming mononuclear cryptates. The Cu(II)-cryptate of L1 further accepts a watermolecule to form [Cu(L1)(OH2)]·(picrate)2·(H2O), i.e., C45H53N11O19Cu. This molecule crystallizes in themonoclinic space group C2/c with a = 34.199(8) Å, b = 12.286(5) Å, c = 23.289(7) Å, β = 93.12(4)°, Z = 8.The O atom of the water molecule is strongly bonded to the Cu(II) ion, while its H atoms are H-bonded to thenearest benzene rings. The UV−vis spectral and magnetic studies of the complexes are consistent with themononuclear nature of the cryptates. Cryptand L1 undergoes diprotonation upon treatment with a mineral acidlike HCl or HClO4. This diprotonated cryptand is found to be a good host for two molecules of water inside thecavity. The diperchlorate salt, [H2L1⊂(H2O)1.5]·(ClO4)2·(H2O)0.75, i.e., C33H51.5Cl2N5O13.25, crystallizes in themonoclinic space group P21/c with a = 12.204(1) Å, b = 11.465(1) Å, c = 28.537(3) Å, β = 91.98(2)°, Z = 4.The cryptand has an ellipsoidal cavity with both the bridgehead N atoms adopting an endo-endo conformation inthe solid state. The water O atoms O(1w) and O(2w) lie in the pseudo 3-fold axis joining the two bridgehead Natoms. Occupancy of O(2w) is found to be 0.5 while that of O(1w) is unity. The water molecules are heldinside the cavity through H-bonding with an ice-like structure. The FAB-mass spectral data and the bond distancesinvolving the water oxygens suggest that both the water molecules are tightly held inside the cavity. The presentcryptate is the first X-ray crystallographically characterized complex with two water molecules inside the cavityof a cryptand.
- Transition metal ions such as Cu(II) and Ni(II) occupy the N4 site of L1 forming mononuclear cryptates. Another structurally similar cryptand L2 where the N4 site is derived from tris(3-aminopropyl)amine behaves similarly. The Cu(II) cryptate of L1 further recognizes a water molecule which is H-bonded to the benzene moieties. Cryptand L1 also recognizes two water molecules in its cavity after protonation. The binding mode of the water molecules beautifully demonstrates the heteroditopic nature of the cryptand.
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