Homochiral, Helical Coordination Complexes of Lanthanides(III) and Mixed-Metal Lanthanides(III): Impact of the 1,8-Naphthalimide Supramolecular Tecton on Structure, Magnetic Properties, and Luminescence

The reactions of the lithium salt of (<i>S</i>)-2-(1,8-naphthal­imido)-3-hydroxy­propanoate (<b>L</b>_<b>ser</b>^–), 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(<b>L</b>_<b>ser</b>)₈­(OH)­(H₂O)]·​(H₂O,​EtOH)_<i>x</i> (<b>1</b>), [Ce₃­(<b>L</b>_<b>ser</b>)₈­(OH)­(H₂O)]·​(H₂O,​EtOH)_<i>x</i> (<b>2</b>), [Sm₃­(<b>L</b>_<b>ser</b>)₈­(OEt)]·​(H₂O,​EtOH)_<i>x</i> (<b>3</b>), [Eu₃­(<b>L</b>_<b>ser</b>)₈­(OEt)]·​(H₂O,​EtOH)_<i>x</i> (<b>4</b>), [Gd₃­(<b>L</b>_<b>ser</b>)₈­(OEt)]·​(H₂O,​EtOH)_<i>x</i> (<b>5</b>), [Tb₃­(<b>L</b>_<b>ser</b>)₈­(OEt)]·​(H₂O,​EtOH)_<i>x</i> (<b>6</b>), and [Dy₃­(<b>L</b>_<b>ser</b>)₈­(OEt)]·​(H₂O,​EtOH)_<i>x</i> (<b>7</b>), respectively. Mixed-metal complexes [Ce_2.3Tb_0.7­(<b>L</b>_<b>ser</b>)₈(OH)]·​(H₂O,​EtOH)_<i>x</i> (<b>8</b>), [Gd_0.4Tb_2.6­(<b>L</b>_<b>ser</b>)₈­(OEt)]·​(H₂O,​EtOH)_<i>x</i> (<b>9</b>), and [Ce_1.4Gd_0.3Tb_1.3­(<b>L</b>_<b>ser</b>)₈(OH)]·​(H₂O,​EtOH)_<i>x</i> (<b>10</b>) were prepared by using two or more types of lanthanides in the solvo­thermal reactions (additional mixed-metal complexes were prepared and characterized by ICP-MS). Single crystals of compounds <b>1</b>–<b>10</b> are isostructural: trinuclear, carboxylate-bonded helicates organized by the non-covalent, π···π stacking interactions of the 1,8-naphthal­imide groups into <i>inter­twined M</i> 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 <b>2</b> showed weak anti­ferro­magnetic ordering below 50 K. All of the complexes, with the exception of <b>2</b>, showed luminescence based on the 1,8-naphthal­imide group. Complex <b>2</b> 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 <b>4