Two complexes comprising 9-coordinate capped square antiprismatic [Ln(NO3)(3)(OH2)(2)(MeOH)] units [Ln(III) Dy 6; Tb 7] are reported in which the metal complexes are hydrogen-bonded to 15C5 (15-crown-5) macrocydes to form supramolecular chains, {[Ln(NO3)(3) (OH2)(2)(MeOH)] (15C5)}(n). Alternating current magnetic susceptibility measurements supported by ab initio studies show field-induced SMM (single molecule magnet) behavior for 6, but rapid relaxation of the magnetization for 7. because of the presence of dominant quantum tunneling processes as evidenced by the presence of a significant calculated tunnel splitting within the ground-state multiplet. Modeling the high-resolution emission spectra for 6 afforded energies of 37 +/- 5 and 28 +/- 5 cm(-1) for the first-excited-state Stark sublevels of the two crystallographically independent Dy1 and Dy2 ions, in excellent agreement with the calculated values of 31 and 21 cm(-1) for Delta E-1 derived from ab initio studies.