Issue 43, 2025, Issue in Progress

Observation of spin-crossover behaviour in Co(ii)-terpyridine complexes possessing π-conjugated substations

Abstract

Exploring new compounds that exhibit spin-state switching under external stimuli is crucial for advancing materials science. However, the feasibility of combining π-conjugated moieties with Co(II)-terpy cation units via an ethynyl group has not yet been investigated. This approach represents a hybridization strategy wherein distinct functional moieties are incorporated into a single coordination metal complex to achieve multifunctionality. In this study, we synthesised a series of Co(II)-terpyridine complexes [Co(R-ethynyl-terpy)2](BF4)2 (R = phenyl for 1, naphthyl for 2, anthracenyl for 3, and pyrenyl for 4), resolved their crystal structures and packing arrangements, and evaluated their magnetic properties using a superconducting quantum interference device magnetometer. These Co(II)-based complexes exhibited thermal spin-crossover behaviour in the solid state. Although complexes 1–4 were luminescent in solution, only complexes 3 and 4 emitted dual monomer and excimer fluorescence in solution due to their substituted π-conjugated moieties. Our findings are expected to serve as a platform for the synthesis of magnetically functional coordination metal compounds based on Co(II) ions for the potential development of photophysical materials.

Graphical abstract: Observation of spin-crossover behaviour in Co(ii)-terpyridine complexes possessing π-conjugated substations

Supplementary files

Article information

Article type
Paper
Submitted
09 Dec 2024
Accepted
14 Sep 2025
First published
29 Sep 2025
This article is Open Access
Creative Commons BY-NC license

RSC Adv., 2025,15, 35892-35898

Observation of spin-crossover behaviour in Co(II)-terpyridine complexes possessing π-conjugated substations

K. Soejima, Y. Sekine, K. Miyake, K. Kiba, Y. Yamaguchi, H. Zenno and S. Hayami, RSC Adv., 2025, 15, 35892 DOI: 10.1039/D4RA08657K

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