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Synergistic Experimental and Theoretical Studies of Luminescent–Magnetic Ln<inf>2</inf>Zn<inf>6</inf> Clusters
Journal
Inorganic Chemistry
ISSN
00201669
Date Issued
2022-01-31
Author(s)
Saha, Sayan
Das, Krishna Sundar
Sharma, Tanu
Bala, Sukhen
Adhikary, Amit
Huang, Guo Zhang
Tong, Ming Liang
Ghosh, Arjit
Das, Benubrata
Rajaraman, Gopalan
Mondal, Raju
Abstract
The present work is part of our ongoing quest for developing functional inorganic complexes using unorthodox pyridyl–pyrazolyl-based ligands. Accordingly, we report herein the synthesis, characterization, and luminescence and magnetic properties of four 3d–4f mixed-metal complexes with a general core of Ln2Zn6 (Ln = Dy, Gd, Tb, and Eu). In stark contrast to the popular wisdom of using a compartmental ligand with separate islands of hard and soft coordinating sites for selective coordination, we have vindicated our approach of using a ligand with overcrowded N-coordinating sites that show equal efficiency with both 4f and 3d metals toward multinuclear cage-cluster formation. The encouraging red and green photolumiscent features of noncytotoxic Eu2Zn6 and Tb2Zn6 complexes along with their existence in nanoscale dimension have been exploited with live-cell confocal microscopy imaging of human breast adenocarcinoma (MCF7) cells. The magnetic features of the Dy2Zn6 complex confirm the single-molecule-magnet behavior with befitting frequency- and temperature-dependent out-of-phase signals along with an Ueff value of ∼5 K and a relaxation time of 8.52 × 10–6 s. The Gd2Zn6 complex, on the other hand, shows cryogenic magnetic refrigeration with an entropy change of 11.25 J kg–1 K–1 at a magnetic field of 7 T and at 2 K. Another important aspect of this work reflects the excellent agreement between the experimental results and theoretical calculations. The theoretical studies carried out using the broken-symmetry density functional theory, ORCA suite of programs, and MOLCAS calculations using the complete-active-space self-consistent-field method show an excellent synergism with the experimentally measured magnetic and spectroscopic data.