Heteroditopic cryptands of tunable cavity size: Imposition of distorted geometry onto copper(II) and nickel(II) and molecular recognition of water molecules

Complexation behavior of a previously described heteroditopic cryptand L-1 and a newly synthesized cryptand L-2 toward transition metal ions is described. The cryptands readily accept a transition metal ion like Cu(LI) or Ni(II) at the Nd end of the cavity forming mononuclear cryptates. The Cu(II)-cryptate of L-1 further accepts a water molecule to form [Cu(L-1)(OH2)].(picrate)(2).(H2O), i.e., C45H53N11O19Cu. This molecule crystallizes in the monoclinic space group C2/c with a = 34.199(8) Angstrom, b = 13.286(5) Angstrom, c = 23.289(7) Angstrom, beta = 93.12(4)degrees. Z = 8, The O atom of the water molecule is strongly bonded to the Cu(II) ion, while its H atom:, are I-I-bonded to the nearest benzene rings. The UV-vis spectral and magnetic studies of the complexes are consistent with the mononuclear nature of the cryptates. Cryptand L-1 undergoes diprotonation upon treatment with a mineral acid like HCl or HClO4. This diprotonated cryptand is found to be a good host for two molecules of water inside the cavity. The diperchlorate salt, [H(2)L(1)subset of(H2O)(1.5)].(ClO4)(2).(H2O)(0.75). i.e., C33H51.5Cl2N5O13.25, crystallizes in the monoclinic space group P2(1)/c with a = 12.204(1) Angstrom. b = 11.465(1) Angstrom, c = 28.537(3) Angstrom, beta = 91.98(2)degrees, Z = 4. The cryptand has an ellipsoidal cavity with both the bridgehead N atoms adopting an endu-endo conformation in the solid state. The water O atoms O(1w) and O(2w) lie in the pseudo 3-fold axis joining the two bridgehead N atoms. Occupancy of O(2w) is found to he 0.5 while that of O(1w) is unity. The water molecules are held inside the cavity through II-bonding with an ice-like structure. The FAB-mass spectral data and the bond distances involving the water oxygens suggest that both the water molecules are tightly held inside the cavity. The present cryptate is the first X-ray crystallographically characterized complex with two water molecules inside the cavity of a cryptand.