Luminescent multiporphyrin molecular square assemblies have been synthesized in high yield from Re(CO)5Cl and a highly soluble dipyridylporphyrin ligand. Both free-base and ZnII-metalated variants of squares have been synthesized. The ZnII-containing squares are capable of strongly binding selected polyimine ligands in CH2Cl2 solution. Advantage has been taken of the effect to construct pentaporphyrin host−guest assemblies.

A new family of molecular squares containing ReI polypyridyl and polypyrazyl centers has been synthesized at quantitative yields via a self-assembly method. Ambient-temperature photophysical studies reveal that two of the squares (4,4‘-bipyridine- and pyrazine-bridged species) readily luminesce in solution from relatively long-lived charge-transfer excited states. These squares expand the growing field of inorganic cyclophane self-assembly chemistry to the octahedral metal systems.

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Rigid macrocycles based on cis bridging ligation of transition metals represent an unusual,'-4 and largely new,5 class of compounds having tremendous promise in host-guest, inclusion, and molecular recognition chemistry. Most of the available systems are (1) derived from pt(I1) or Pd(I1) triflate species, (2) tetranuclear with respect to metal content, and therefore, (3) arranged in square or box-like geometries, with metal atoms defining the comers. We report a simple, but potentially very useful, variant and extension of this theme: incorporation of visible-light-addressable, luminescent metal-ligand components within a square assembly. Induction of photoluminescent characteristics is particularly attractive in the context of eventual molecular sensing applications because it suggests an altemative to 'H NMR spectroscopy for detection of guest inclusion. Induction of luminescence also opens up the possibility of electronic excited state reactivity and possible manipulation of reactivity by encapsulated guests.The light-emitting square complex, 1; was prepared by combining the chromophore fac-Re(CO)F1(4,4'-bpy)2 (2)6 (105 mg, 0.170 "01) (4,4'-bpy = 4,4'-bipyridine) with Pd(dppp)-(triflate)zId (139 mg, 0.170 m o l ) (dppp = 1,3-(diphenylphosphino)propane) in 50 mL of dry CH2C12. After 12 h of stirring, the pale yellow product was collected as a powder on a glass frit, washed with methylene chloride, and dried under vacuum. The yield was 83%. Elemental analysis data are consistent with the formation of either 1 or a larger assembly with 1:l Re:Pd stoichiometry.' FAB+ mass spectral measurements (m-NBA) yielded intense peaks at m/z = 2871.7 (2871.2 expected for l*H+), 2721.0 (1triflate) and 2564.9 (1triflate -4,4'bpy), thereby establishing the tetranuclear metal content of the compound. No peaks for compounds of higher mass (e.g., hexanuclear or octanuclear complexes) were found. FT-IR and 'H NMR measurements (supporting information) yielded additional data supportive of molecular square formation.* Figure 1 shows that the lowest energy transition in the electronic absorption spectrum of 2 is shifted substantially red by formation of the square. The shift is similar to that observed upon ligand protonation in 26 and is consistent with assignment (1) (a) Fujita, M.; Yakazi, J.; Ogura, K. (5) Nevertheless, at least one early report exists: Stricklen, P. M.; Volcko, E. J.; Verkade, J. G.

Described are the preparation and functional characterization of nanocrystalline and/or amorphous thin films comprising of neutral "molecular squares" of the form [Re(CO) 3 (Cl)(µ-L)] 4 (L ) difunctional imine or azine ligand). The films are strongly adherent, stable in aqueous media, and characterized by comparatively few pinhole defects. Electrochemical transport experiments show that the materials are exceptionally porous with respect to sufficiently small solution-phase permeants but blocking toward larger permeants. Related thin-film experiments based on monometallic "corner" materials indicate efficient exclusion of all candidate permeant molecules evaluated. For the title materials, these experiments, together with additional electrochemical probe experiments, indicate that (1) membranelike permeation via pores or tunnels of about nanometer diameter is the primary mode of transport of molecular and ionic species through thin films and (2) the transportrelevant pore or tunnel diameter is defined by the cavity dimensions for the component molecular square. The crystal structure of a single isomer of [Re(CO) 3 (Cl)(µ-4,4′-bipyridine)] 4 is also reported. A packing view down the c axis of the tetragonal unit cell shows that the molecules, which are significantly puckered in the crystalline state, are arranged with cavities aligned to generate infinite zeolite-like channels.