Countercation-Controlled Nuclearity of Zr/Hf Peroxo Oxalates

Abstract

Understanding fundamental differences between zirconium and hafnium chemistry contributes to our fundamental understanding of the periodic table and leads to devising necessary separations for high-precision nuclear and microelectronics applications, developing water-based nanolithographic processes, and creating new robust metal−organic frameworks for catalysis and separations. Here we crystallize a rich matrix of polynuclear Zr and Hf species differentiating in complexation with peroxide and oxalate in mild acid, where the countercations influence polymerization. Hf only complexes oxalate, yielding polymericNa 6 [Hf 2 (OH) 2 (C 2 O 4 ) 6 ], and Li 2 K 4 [Hf 2 (OH) 2 (C 2 O 4 ) 6 ] and mononuclear K 4 Hf(C 2 O 4 ) 4 , Rb 4 Hf(C 2 O 4 ) 4 , and Cs 4 Hf-(C 2 O 4 ) 4 . Zr complexes both peroxide and oxalate to yield the ring structures (N-( C H 3 ) 4 ) 6 [ Z r 6 ( O 2 ) 6 ( O H ) 6 ( C 2 O 4 ) 6 ] , L i 1 2 [ Z r 8 ( O 2 ) 1 2 ( O H ) 4 ( C 2 O 4 ) 8 ] , K 18 [Zr 12 (O 2 ) 18 (OH) 6 (C 2 O 4 ) 12 ], and Rb 24 [Zr 16 (O 2 ) 24 (OH) 8 (C 2 O 4 ) 16]. The Zr ring nuclearity increases with countercation size, while Hf polymerization decreases with increasing countercation size. The Zr rings feature nine-coordinate face-sharing polyhedra in both solution and the solid state, unprecedented in Zr coordination complexes. These studies describe differentiating the coordination chemistry of Zr/Hf, exploiting simple aqueous reagents that could be further developed for aqueous synthesis of materials as well as challenging chemical separations.

Differentiating Zr/HfIV Aqueous Polyoxocation Chemistry with Peroxide Ligation

“…This suggests that Zrbound water may be more acidic than Hf-bound water, as one fundamental difference between Zr and Hf leading to different crystallized group 4 peroxide clusters. In a concurrent study of Hf and Zr in mildly acidic peroxide-oxalate solutions,43 Zrperoxide-oxalate species or Hf-oxalate species are crystallized. This study suggests Zr forms more stable bonds with peroxide than Hf, consistent with the currently described Raman studies showing a maximum bonding ratio of 0.5:1 peroxide:Hf and >1:1 peroxide:Zr.While Hf/Zr species scrambling is evident in the abovedescribed study, we cannot be sure if this is a direct result of the methanol, the peroxide, or even the ionization process.…”

Aqueous Stability of Zirconium Clusters, Including the Zr(IV) Hexanuclear Hydrolysis Complex [Zr6O4(OH)4(H2O)24]12+, from Density Functional Theory

“…Our thermodynamic analysis suggests that although aqueous synthesis of a Zr hexamer with only water-based ligands is challenging, formation of the Zr hexamer by means of counterions or ligation may be possible. Fruitful areas for future research on this topic include an investigation of such counterion effects, and an exploration of the similarities and differences between the system studied here and aqueous hafnium clusters, which have a similar chemistry to zirconium. ,,, We hope that the approach demonstrated herein will contribute to simpler and more sustainable synthesis strategies for MOFs.…”

“…Fruitful areas for future research on this topic include an investigation of such counterion effects, and an exploration of the similarities and differences between the system studied here and aqueous hafnium clusters, which have a similar chemistry to zirconium. 21,22,31,83 We hope that the approach demonstrated herein will contribute to simpler and more sustainable synthesis strategies for MOFs.…”

“…They have numerous useful applications in catalysis, , medicine, , precursors for thin-film deposition, , flash memory devices, switchable transparent films, and high-resolution nanopatterning, , to name a few. These discrete molecular metal oxides can vary in size and geometry, forming coordination complexes that are linked via oxo and hydroxo ligands. , The examples of metals that have been shown to form metal-oxide clusters include group 5 and 6 polyoxometalates (Mo VI , W VI , V VI , Nb V , and Ta V ), , other transition metals (Fe III , Cu II , Zr IV , Hf IV , and Ti IV ), − and post-transition metals (Al III , Ga III , and Sn IV ). ,− …”

Polyoxocationic antimony oxide cluster with acidic protons

“…In this study, we report on [H 19.0+ (HSbO) that form a face-centered cubic (fcc) packed lattice with [H 2.1 Sb 2.1 I 8 O 6 ] 11.6− and [Sb 0.76 I 6 ] 3.7− clusters at the interstitial sites (Fig. 1A).…”