Assessing Guest Selectivity within Metallacrown Host Compartments

Abstract

Abstract15‐MC‐5 complexes associate in the solid state to form chiral compartments capable of binding guests. Using small molecular yardsticks, we are able to assess the size restrictions of these structures. Dicarboxylate guests that are too short to span the GdIII ions are stabilized by solvates that hydrogen bond to the uncoordinated carboxylate, while guests that are too long destroy the weakly associated structure. We also demonstrate that all that is required for guest encapsulation is unsaturation of the chain connection carboxylates rather than necessitating the presence of aromaticity. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Magnetic Properties of LnIII–CuII 15‐Metallacrown‐5 Dimers with Terephthalate (LnIII = Pr, Nd, Sm, Eu)

“…The Ln III ions in 1 – 4 are all octacoordinate, with a pentagonal array of equatorial donor atoms, plus an axial‐O on one direction and a pair of O‐donors trans to it. The equatorial Ln–O bond lengths in 1 – 4 range from 2.388(3) to 2.497(5) Å, which is consistent with previously reported data , , , . The [LnCu 5 (GlyHA) 5 ] 3+ units in dimeric 1 – 4 are connected by bridging terephthalates, which are monodentately coordinated to the Ln III ions of two metallacrown fragments [Ln–O p‐bdc are 2.254(14)–2.51(3) Å].…”

“…Formation of discrete dimers {LnCu 5 } 2 with dicarboxylates is quite typical for 15‐metallacrowns‐5 and has been confirmed both in the solid state and in solution for aromatic (terephthalate, dithiophenedicarboxylate, naphthalenedicarboxylate), and aliphatic (adipate, pimelate, muconate, fumarate), dicarboxylates. However, interactions of 15‐metallacrowns‐5 with the same polycarboxylate linkers under quite similar reaction conditions also led to the formation of 1D‐, , [29b], [30a], or 2D‐polymers, tetramers and discrete complexes, where the metallacrowns are non‐oligomerised. [29b] The diversity of oligomerisation levels which were found for 15‐metallacrown‐5 units can presumably result from several factors, such as: i ) the ionic radii and preferred coordination number of the lanthanide ion in the center of the 15‐metallacrown‐5 fragment; ii ) the size and nature of peripheral substituents in the hydroxamate ligand; iii ) the solvent system used for crystallisation, etc .…”

“…However, interactions of 15‐metallacrowns‐5 with the same polycarboxylate linkers under quite similar reaction conditions also led to the formation of 1D‐, , [29b], [30a], or 2D‐polymers, tetramers and discrete complexes, where the metallacrowns are non‐oligomerised. [29b] The diversity of oligomerisation levels which were found for 15‐metallacrown‐5 units can presumably result from several factors, such as: i ) the ionic radii and preferred coordination number of the lanthanide ion in the center of the 15‐metallacrown‐5 fragment; ii ) the size and nature of peripheral substituents in the hydroxamate ligand; iii ) the solvent system used for crystallisation, etc . Of course, if several different products form in the reaction mixtures, only the less soluble ones tend to be isolated during crystallisation.…”

“…It was previously reported that reactions between different 15‐metallacrown‐5 complexes with terephthalate led to the formation of discrete non‐oligomerised and dimerised complexes, 1D‐ or 2D‐polymers depending on the peripheral substituent on the hydroxamic acid and on the central lanthanide(III) ion in the 15‐metallacrown‐5 unit , ,. [28a], , [30a]…”

Influencing the Size and Anion Selectivity of Dimeric Ln3+[15-Metallacrown-5] Compartments through Systematic Variation of the Host Side Chains and Central Metal

“…Naphthalene dicarboxylate and bithiophene dicarboxylate (btDC) (guest lengths = 8.00 and 9.24 Å, respectively) disrupt compartment formation by preventing formation of associative π-stacking interactions between the two MCs. 56 containers. We hypothesized that the constraints on compartment height originate from the length of the phenyl side chain.…”