Framework complexes of group 2 metals organized by homochiral rods and π···π stacking forces: a breathing...

The reactions of the potassium salts of the ligands (S)-2-(1,8-naphthalimido)propanoate (KL(ala)), (S)-2-(1,8-naphthalimido)-3-hydroxypropanoate (KL(ser)), and (R)-2-(1,8-naphthalimido)propanoate (KL(ala)*), enantiopure carboxylate ligands containing a 1,8-naphthalimide π···π stacking supramolecular tecton, and, in the case of L(ser)(-), an alcohol functional group with calcium or strontium nitrate under solvothermal conditions produce crystalline [Ca(L(ala))2(H2O)]·(H2O) (1); [Ca(L(ser))2]·(H2O)2 (2); [Sr(L(ala))2(H2O)]·(H2O)3 (3); [Sr(L(ala)*)2(H2O)]·(H2O)3 (3*); and [Sr(L(ser))2(H2O)] (5). Placing 3 under vacuum removes the interstitial waters to produce [Sr(L(ala))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 unit (SBUs) central cores. Supramolecular π···π stacking interactions between 1,8-naphthalimide rings link adjacent rod SBUs into three-dimensional structures for 1, 3, 4, and 5 and two-dimensional structure for 2. Compounds 1 and 3 have open one-dimensional 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. Infrared 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 (1)H, (2)H, and (13)C solid-state NMR spectroscopy, and thermal and luminescence data are reported on all of the complexes.