Supramolecular Coordination Networks of s- and f-Block Metals Featuring the 1,8-Naphthalimide Tecton

The reactions of (S)-2-(1,8-naphthalimido)propanoic acid (HLala), and (S)-2-(1,8- naphthalimido)-3-hydroxypropanoic acid (HLser), protonated forms of ligands that contain a carboxylate donor group, an enantiopure chiral center and a 1,8-naphthalimide π...π stacking supramolecular tecton and in the case of HLser an alcohol functional group, with the appropriate alkali metal hydroxide followed by a variety of crystallization methods leads to the formation of crystalline K(Lala)(MeOH) (1), K(Lala)(H2O) (2), Na(Lala)(H2O) (3), KLser (4), CsLser (5) and CsLala (6). Each of these new complexes has a solid state structure based on six-coordinate metals linked into homochiral helical rod SBU central cores. In addition to the bonding of the carboxylate and solvent (in the case of Lser the ligand alcohol) to the metals, both oxygens on the 1,8-naphthalimide act as donor groups. One naphthalimide oxygen bonds to the same helical rod SBU as the carboxylate group of that ligand forming a chelate ring. The other naphthalimide oxygen bonds to adjacent SBUs. In complexes 1-3, this inter-rod link has a square arrangement bonding four other rods forming a three-dimensional enantiopure MOF structure, whereas in 4-6 this link has a linear arrangement bonding two other rods forming a twodimensional, sheet structure. In the latter case, the third dimension is supported exclusively by interdigitated π…π stacking interactions of the naphthalimide supramolecular tecton, forming enantiopure supramolecular MOF solids. Compounds 1-3 lose the coordinated solvent when heating above 100 °C. For 1, the polycrystalline powder reverts to 1 only by recrystallization from methanol, whereas compounds 2 and 3 undergo gas/solid, single-crystal to single-crystal transformations to form dehydrated compounds 2* and 3*, and rehydration occurs when crystals of these new complexes are left out in air. The reversible single-crystal to single-crystal transformation of 2 involves the dissociation/coordination of a terminal water ligand, but the case of 3 is remarkable considering the water that is lost is the only bridging ligand between the metals in the helical rod SBU and a carboxylate oxygen that is a terminal ligand in 3 moves into a bridging position in 3* to maintain the homochiral helical rods. Both 2* and 3* contain five-coordinate metals. There are no coordinated solvents in compounds 4-6, in two cases by designed ligand modification, which allows them to have high thermal stability. Compounds 1-3 did not exhibit observable SHG efficiency at an incident wavelength of 1064 nm, but compounds 4-6 did exhibit modest SHG efficiency for MOF-like compounds in the range of 30 x α-SiO2. The reactions of the potassium salts of the ligands (S)-2-(1,8- naphthalimido)propanoate (KLala) and (S)-2-(1,8-naphthalimido)-3-hydroxypropanoate (KLser) and (R)-2-(1,8-naphthalimido)propanoate (KLala*), enantiopure carboxylate ligands containing a 1,8-naphthalimide π...π stacking supramolecular tecton and in the case of Lser - an alcohol functional group, with calcium or strontium nitrate under solvothermal conditions produce crystalline [Ca(Lala)2(H2O)]·(H2O) (1), [Ca(Lser)2]·(H2O)2 (2), [Sr(Lala)2(H2O)]·(H2O)3 (3), [Sr(Lala*)2(H2O)]·(H2O)3 (3*) and [Sr(Lser)2(H2O)] (5). Placing 3 under vacuum removes the interstitial waters to produce [Sr(Lala)2(H2O)] (4) in a single-crystal to single-crystal transformation; introduction of water vapor to 4 leads to the reformation of crystalline 3. Each of these new complexes has a solid-state structure based on homochiral rod secondary building units (SBUs) central cores. Supramolecular π…π stacking interactions between 1,8-naphthalimide rings link adjacent rod SBUs into 3D structures for 1, 3, 4 and 5 and 2D structure for 2. Compounds 1 and 3 have open 1D channels along the crystallographic c axis that are occupied by disordered solvent. For 3, these channels close and open in the reversible single-crystal conversion to 4; the π…π stacking interactions of the naphthalimide rings facilitate this process by rotating and slipping. IR spectroscopy demonstrated that the rehydration of 4 with D2O leads to 3d8 and the process of dehydration and rehydration of 3d8 with H2O leads to 3, thus showing exchange of the coordinated water in this process. These forms of 3 and 4 were characterized by 1H, 2H and 13C solid-state NMR spectroscopy and thermal and luminescence data are reported on all of the complexes. The reactions of (1,8-naphthalimido)ethanoic acid (HLgly), and (S)-2-(1,8- naphthalimido)-3-hydroxypropanoic acid (HLser), protonated forms of ligands that contain a carboxylate donor group and a 1,8-naphthalimide π...π stacking supramolecular tecton, with cesium hydroxide followed by solvothermal treatment in ethanol led to the formation of crystalline Cs(Lgly) (1) and Cs(Lene) (2), where the Lene - ligand, 2-(1,8- naphthalimido)acrylate, is formed from the dehydration of the HLser starting material. The X-ray studies show that 1 crystallizes in the monoclinic space group C2/c with unit cell dimensions a = 30.430(7) Å, b = 4.9820(12) Å, c = 16.566(4) Å, β = 101.951(4)o and 2 in the monoclinic space group P21/n with unit cell dimensions a = 13.6049(15) Å, b = 6.8100(8) Å, c = 14.4187(16) Å, β = 105.345(2)o. The solid state structure of 1 contains two types of 6-coordinate cesium cations linked into sheets by bridging carboxylate oxygen atoms. One cation has a distorted octahedral environment, while the other is in an unusual planar, hexagonal O6-coordination geometry. The latter geometry is stabilized on both sides of the plane by η2-coordination of naphthalimide rings. The 1,8- naphthalimide rings are involved in intra-sheet π…π stacking interactions. The O6 coordination sphere of complex 2 is distorted and only half-filled with the oxygen atoms, which link the cations into rods that are further linked into sheets by bridging interactions of naphthalimide carbonyls with cesium cations from adjacent rods. The open face on the cation has unique η2:η1 interactions with two methylene groups in the ligands. These sheets are linked into a 3D supramolecular structure by interdigitated 1,8-naphthalimide rings involved in strong π…π interactions. Both complexes show naphthalimide based fluorescence. The reactions of the lithium salt of (S)-2-(1,8-naphthalimido)-3-hydroxypropanoate (Lser -), an enantiopure carboxylate ligand containing a 1,8-naphthalimide π...π stacking supramolecular tecton and an alcohol functional group, with La(NO3)3, Ce(NO3)3, SmCl3, Eu(NO3)3, Gd(NO3)3, Tb(NO3)3 and Dy(NO3)3 under solvothermal conditions (water/ethanol) produced single crystals (characterized by single crystal X-ray crystallography) of [La3(Lser)8(OH)(H2O)]•(H2O, EtOH)x (1), [Ce3(Lser)8(OH)(H2O)]•(H2O, EtOH)x (2), [Sm3(Lser)8(OEt)]•(H2O, EtOH)x (3), [Eu3(Lser)8(OEt)]•(H2O, EtOH)x (4), [Gd3(Lser)8(OEt)]•(H2O, EtOH)x (5), [Tb3(Lser)8(OEt)]•(H2O, EtOH)x (6) and [Dy3(Lser)8(OEt)]•(H2O, EtOH)x (7), respectively. Mixed-metal complexes [Ce2.3Tb0.7(Lser)8(OH)]•(H2O, EtOH)x (8), [Gd0.4Tb2.6 (Lser)8(OEt)]•(H2O, EtOH)x (9) and [Ce1.4Gd0.3Tb1.3(Lser)8(OH)]•(H2O, EtOH)x (10) were prepared by using two or more types of lanthanides in the solvothermal reactions (additional mixed-metal complexes were prepared and characterized by ICPMS). Single crystals of compounds 1-10 are isostructural: trinuclear, carboxylate-bonded helicates organized by the noncovalent, π...π stacking interactions of the 1,8- naphthalimide groups into intertwined M helices, with a pitch of 56 Å, that are further arranged into a three dimensional supramolecular framework by additional π...π stacking interactions. Magnetic measurements of several compounds were as expected for the metal(s) present, indicating no significant interactions between metals within the helicates. The Ce complex 2 showed weak antiferromagnetic ordering below 50 K. All of the complexes, with the exception of 2, showed luminescence based on the 1,8- naphthalimide group. Complex 2 has no emission and complexes with mixed Ce/Tb ratios showed significant quenching of the naphthalimide-based luminescence, as quantitated with solid state, absolute quantum yield measurements of these mixed-metal and the pure metal complexes. Lanthanide based luminescence was only observed for the Eu complex 4. The new ligand 5-(1,8-naphthalimido)isophthalate (L135 2-), containing two carboxylate donor groups and the 1,8-naphthalimide supramolecular tecton, has been used under solvothermal conditions to prepare a series of group 2, lanthanide and actinide metal complexes: [Ca4(L135)4(H2O)8]·(H2O)9.5(DMF)2.6 (1), Ba(L135)(H2O)1.5(DMF)0.5 (2), La2(L135)3(DMF)4 (3), Ce2(L135)3(DMF)4 (4), Eu2(L135)3(DMF)4 (5), Tb2(L135)3(DMF)4 (6), [UO2(L135)(DMF)]·(py)0.5(EtOH)0.5 (7) and Th(L135)(NO3)2(DMF)2]·(DMF)2 (8). The solid state structure of the calcium complex 1 is based on helical rod-shaped secondary building-units (SBUs) of edge-shared polyhedra bridged by oxygens from the carboxylate groups. The crystals are racemic, with the one-dimensional (1D) helical rods organized by π…π stacking interactions of the naphthalimide group into a 3D supramolecular framework (SMOF) structure. Although the structure of the barium complex 2 also contains rod-shaped SBUs, the rods are linked through the aryl backbone of the ditopic L135 2- ligands into 2D sheets. The sheets are further engaged in naphthalimide π…π stacking interactions to build a 3D SMOF. The lanthanide complexes 3-6 are isostructural, based on binuclear SBUs linked by the ligands into a square-shaped grid pattern, with π-stacking interactions linking adjacent sheets to generate a 3D SMOF. The uranium(VI) complex 7 contains 7-coordinate pentagonal bipyramid uranyl cations bridged by the ligands into one dimensional ribbons. The solid state structure of the thorium(IV) complex 8 consists of 10-coordinate thorium cations, also bridged by the ligands into one dimensional ribbons. Both of these actinide structures are organized into only 2D supramolecular sheets by π-stacking interactions. Compounds 1, 2, 3, 6 and 8 exhibit solid-state luminescence dominated by the naphthalimide chromophore in the ligand. The group 2 complexes are slightly red-shifted and the lanthanum complex 3 and the thorium complex 8 slightly blue-shifted with respect to the ligand. The terbium compound, 6, is greatly blue-shifted by ~75 nm and naphthalimide sensitization of the metal emission occurs for the europium complex 5. The cerium(III) and uranyl(VI) compounds 4 and 7 have no solid state emission