Conversion of Metal Pyrazolate/(Hydr)oxide Clusters into Nanojars: Solution vs Solid-State Structure and Magnetism

Nanojars are a class of anion binding and extraction agents composed of a series of [Cu(μ-OH)(μ-pz)] (pz = pyrazolate; n = 26-36) supramolecular metal-organic complexes. In contrast to other anion binding agents amenable to liquid-liquid extraction, nanojars only form by self-assembly around the target anion, and guest-free nanojar hosts cannot be isolated. An extraordinary binding strength toward highly hydrophilic anions such as carbonate and sulfate was demonstrated by the inability of Ba²⁺ ions to precipitate the corresponding insoluble barium salts from nanojars. Herein, we provide an additional proof for the superior robustness of the nanojar framework based on competition experiments with other transition metal pyrazolate/(hydr)oxide complexes. In addition to the mass spectrometric characterization, we present variable-temperature nuclear magnetic resonance studies with an emphasis on the influence of the paramagnetic Cu²⁺ centers on ¹H hyperfine shifts, along with X-ray crystallographic analysis of two polymorphs of (MePh₃P)₂[CO₃⊂{Cu(OH)(pz)}₂₇], including the highest (cubic) symmetry nanojar crystal lattice obtained to date as well as magnetism studies for the first time. Furthermore, we provide evidence for the first molybdate-incarcerating nanojars, [MoO₄⊂{Cu(μ-OH)(μ-pz)}]^2- (n = 28, 31-33), formed by rearrangement from [Mo^VI₈O₁₂(μ-O)₉(μ-pz)₆(pzH)₆·3pzH] in the presence of Cu²⁺ ions.