Series of lanthanide-containing metallic coordination complexes are frequently presented as structurally analogous, due to the similar chemical and coordinative properties of the lanthanides. In the case of chiral (LnIII[15-MC N(L-pheHA)-5])3+ metallacrowns (MCs), which are well established supramolecular hosts, the formation of dimers templated by a dicarboxylate guest (muconate) in solution of neutral pH is herein shown to have a unique dependence on the identity of the MC's central lanthanide. Calorimetric data and nuclear magnetic resonance diffusion studies demonstrate that MCs containing larger or smaller lanthanides as the central metal only form monomeric host-guest complexes whereas analogues with intermediate lanthanides (for example, Eu, Gd, Dy) participate in formation of dimeric host-guest-host compartments. The driving force for the dimerization event across the series is thought to be a competition between formation of highly stable MCs (larger lanthanides) and optimally linked bridging guests (smaller lanthanides). 相似文献
The {Cr8} metallacrown [CrF(O2CtBu)2]8, containing a F‐lined internal cavity, shows high selectivity for CO2 over N2. DFT calculations and absorption studies support the multiple binding of F‐groups to the C‐center of CO2 (C⋅⋅⋅F 3.190(9)–3.389(9) Å), as confirmed by single‐crystal X‐ray diffraction. 相似文献
Two bowl‐shaped cavities , each having three OH? hydrogen‐bond donors at its base, are present in double‐cone‐shaped metallacrown anion host [Co6(μ‐OH)6(μ‐L)6]m+ ( 1 m + ; HL=3{5}‐(pyrid‐2‐yl)‐5{3}‐(tert‐butyl)pyrazole). Depending on its affinity for the anions present, it can be isolated in its CoIII3CoII3 (m=3; e.g., 1 (ClO4)3) and CoIII2CoII4 (m=2; e.g., 1 (BF4)2 ? n H2O) oxidation states. See picture for photographs of isolated salts.
A novel competitive binding assay was implemented to monitor the binding of a redox inactive substrate to a redox inactive metallacrown host based on its competition with ferrocene carboxylate (FcC?) using cyclic voltammetry (CV). First, the binding of FcC? to LnIII[15‐MC‐5] (LnMC) hosts was characterized by cyclic voltammetry. It was shown that the voltammetric half wave potentials, E1/2, shifted to more positive potentials upon the addition of LnMC. The explicit dependence of E1/2 with the concentration of LnMC was used to determine the association constants for the complex. The FcC? binding strength decreased with larger central lanthanide metals in the LnMC hosts, and substantially weaker binding was observed with LaIII. X‐ray crystallography revealed that the hydrophobic host cavity incompletely encapsulated FcC? when the guest was bound to the nine‐coordinate LaIII, suggesting the LnMC’s ligand side chains play a substantial role in guest recognition. With knowledge of the MC‐FcC? solution thermodynamics, the binding affinity of a redox inactive guest was then assessed. Addition of sodium benzoate to a LnMC and FcC? mixture resulted in E1/2 shifting back to the value observed for FcC? in the absence of LnMC. The association constants between benzoate and LnMC’s were calculated via the competitive binding approach. Comparison with literature values suggests this novel assay is a viable method for determining association constants for host–guest systems that exhibit the proper electrochemical behavior. Notably, this CV competitive binding approach does not require the preparation of a modified electrode or a tethered guest, and thus can be generalized to a number of host–guest systems. 相似文献
A 12‐metallacrown‐4 (MC) complex was designed and employed as the building block in the synthesis of coordination polymers, one of which is the first permanently porous MC architecture. The connection of the four‐fold symmetric MC subunits by CuII nodes led to the formation of 2D layers of metallacrowns. Channels are present in the crystalline architecture, which exhibits permanent porosity manifested in N2 and CO2 uptake capacity. 相似文献