Complexation properties of heteroditopic cryptands towards Cu2+, Zn2+, Cd2+, and Pb2+ in aqueous solution: Crystal structures of [(H(5)L1)(ClO4)(5)]center dot 4 H2O and [(NiL2Cl)Cl]center dot 5.5 H2O center dot CH3OH

The protonation and metal ion (Cu2+, Zn2+, Cd2+, Pb2+) complexation abiliti es of three heteroditopic cryptands in solution are described and the relev ant equilibrium constants are reported. The two distinct binding subunits o f the ligands act cooperatively in the coordination of M(H2O)(2+) (M = meta l ion) species. The cryptand L1 binds five protons in very acidic solution and crystallizes as [(H(5)L1)(ClO4)(5)]. 4 H2O in the monoclinic space grou p P2(1)/n with a = 14.281(4), b = 14.313(7), c = 24.082(8) Angstrom, beta = 92.00(2)degrees, Z = 4, R = 0.079, and wR2 = 0.2010. The molecule shows an endo-endo conformation with a pseudo-threefold symmetry axis passing throu gh the two bridgehead nitrogen atoms. All the cryptands (L1-L3) readily for m inclusion complexes with Cu2+, Ni2+ Zn2+, Cd2+, and Pb2+ ions at the tren end of the cavity. The crystal structure of [(NiL2Cl)Cl]. 5.5 H2O . CH3OH is also reported [C2/c, a = 26.671(6), b = 16.784(4), c = 18.591(8) Angstro m, beta = 101.0106(14)degrees, Z = 8, R = 0.091, and wR2 = 0.1424]. The Ni- II ion resides in a trigonal-bipyramidal coordination environment with the equatorial sites occupied by the three secondary nitrogen atoms of the cryp tand and the axial sites occupied by a bridgehead nitrogen atom and a Cl- i on.