pH manipulates the assembly of a series of dysprosium clusters with subtle differences

Abstract

When reaction conditions change, products with different shapes and connections are usually obtained. Thus, the fine-tuning of structures in crystal engineering is challenging. We used the bisacylhydrazone ligand (H₄L¹, N′²,N′⁹-bis((E)-2-hydroxybenzylidene)-1,10-phenanthroline-2,9-dicarbohydrazide) with multiple coordination sites to react with Dy(OAc)₃·6H₂O under different pH conditions and subsequently obtain three pentanuclear dysprosium clusters 1–3 with the same shape. Fine-tuning the pH of the reaction solution resulted in different coordination environments of the metal center Dy5 in the structure of clusters 1–3. When the pH of the reaction solution was 6.4, only cluster 1 was obtained, and its Dy5 in the coordination environment of NO₆ was provided by the ligand (L¹)⁴⁻, the OH⁻ bridge, and OAc⁻. When the pH was 6.6, only the pentanuclear cluster 2 was obtained, and its Dy5 in the NO₇ coordination environment was provided by the ligand (L¹)⁴⁻, OH⁻ bridge, OAc⁻, and H₂O coordinated by the end group. When the pH was 9.0, the metal center Dy5 of the obtained cluster 3 was in the NO₇ coordination environment provided by the ligand (L¹)⁴⁻, the bridge OAc⁻, and the end-group coordination CH₃OH. In addition, we changed the ligand to H₄L² (N′²,N′⁹-bis((E)-2-hydroxy-3-methylbenzylidene)-1,10-phenanthroline-2,9-dicarbohydrazide) with a –CH₃ substituent. When the pH was 6.8, the pentanuclear dysprosium cluster 4 with the same shape was also obtained. The metal center Dy5 of cluster 4 was in the coordination environment of NO₆ provided by the ligand (L²)⁴⁻, CH₃O⁻, and OAc⁻. When the pH was 9.2, only the hexanuclear dysprosium cluster 5, whose shapes and connections are completely different from clusters 1–4 and formed by CO₃²⁻ bridges, was obtained. The CO₃²⁻ source in the structure of cluster 5 was the same as the CO₂ in the air. These examples of liquid–gas reaction in solvothermal reaction are rare. Furthermore, the increase in the steric hindrance of the substituents on the ligand is not conducive to the fine-tuning of the structure of the cluster but is conducive to the formation and connection of clusters with completely different shapes. As far as we know, this study is the first to use pH in manipulating the fine-tuning of a series of lanthanide clusters with the same shape.