Synthesis and characterization of metal-organic frameworks organized by the strong pi-pi stacking 1,8-naphthalimide synthon

A new hetero-bifunctional ligand designed to form supramolecular structures with a combination of covalent and noncovalent forces has been prepared. The ligand, (1,8-naphthalimide)CH2C6H4CH 2OCH2C(pz)3 (Ltris, pz = pyrazolyl ring), contains both a tris(pyrazolyl)methane coordination unit and a 1,8-naphthalimide strong pi···pi stacking unit. The reactions of iron(II), copper(II) and cadmium(II) tetrafluoroborate salts with two equivalents of Ltris yield [Fe(L tris)2](BF4)2 (1), [Cd(Ltris)2](BF4)2 (2) and [Cu(Ltris)2](BF 4)2 (3), respectively. Vapor diffusion crystallization yielded two pseudopolymorphs for 1.;The interaction of the two naphthalimide groups is directionally specific; they are oriented head to tail with substantial overlap of the parallel rings. The twisting of the side chains at 30° for syn- 1 leads to a helical structure, whereas the 180° orientation of the side chains in anti-1 leads to a linear structure. The cadmium(II) complex is isostructural to syn-1 and the copper(II) is isostructural to anti-1. Although the supramolecular structures of these two compounds are similar to the matched iron(II) complexes because of the similar orientations of the side-chains and the consistent noncovalent interactions of the naphthalimide synthon, the larger size of cadmium(II) leads to a highly distorted structure about the metal. The copper(II) structure is also distorted, as expected for a d9 complex.;Shorter, more rigid tri- and tetrafunctional enantiopure ligands have been prepared from commercially-available 1,8-naphthalic anhydride and the amino acids L-alanine, R-phenylglycine, and L-asparagine to produce (S)-2-(1,8-naphthalimido)propanoic acid (HLala), (R)-2-(1,8-naphthalimido)-2-phenylacetic acid (HLphg), and (S)-4-amino-2-(1,8 naphthalimido)-4-oxobutanoic acid (HLasn), respectively. Reactions of Lala- with copper(II) acetate under a variety of solvent conditions has lead to the formation and characterization by X-ray crystallography of three similar copper(II) paddlewheel complexes with different axial ligands, Cu2(Lala) 4(THF)2] (1), [Cu2(Lala )4(HLala)] (2) and [Cu2(Lala)4(py)(THF)] ( 3). A similar reaction using THF and Lphg - leads to the formation of [Cu2(Lphg) 4(THF)2] (4). With the exception of a disordered component in the structure of 4, the naphthalimide groups in all of these compounds are arranged on the same side of the square, central paddlewheel unit, forming what is known as the chiral crown configuration. The shape of the four naphthalimide groups that form this chiral crown pocket on one end of the dimers varies with the axial ligand, being fairly narrow and symmetrical when THF is the axial ligand and expands and is more asymmetric with larger axial ligands. These results demonstrate an enatioselective single-crystal to single-crystal gas/solid-mediated transformation is taking place in the chiral pocket of 5. They also show the large pores in the structure of 5 allow this exchange in the gas/solid phases with the large (S)-ethyl lactate molecule. These exchanges are also supported by the "flexibility" imparted to these solid-state structures by the pi···pi stacking interactions of the 1,8-naphthalimide supramolecular synthon. (Abstract shortened by UMI.)...