Aqueous and Solid Phase Synthesis of [Ni(Me3en)(acac)]BPh4 and its Solvatochromic Properties: A Laboratory Experiment for First-Year Undergraduates

A laboratory experiment that involves the aqueous and solid phase synthesis, characterization, and solvatochromic properties exploration of red complex [Ni(Mei₃en)(acac)]BPh₄ has been developed for first-year undergraduates in the College of Chemistry and Chemical Engineering at Xiamen University. In contrast to previously reported synthesis methods (Fukuda, Y. Studies on mixed chelates─II Mixed nickel(II) chelates with N,N,N′,N′-tetramethylethylenediamine and β-diketones. J. Inorg. Nucl. Chem. 1972, 34, 2315–2328; Funasako, Y. Thermochromic and solvatochromic Nafion films incorporating cationic metal-chelate complexes. Chem. Comm 2013, 49, 4688–4690; Hosokawa, H. Colorimetric Humidity and Solvent Recognition Based on a Cation-Exchange Clay Mineral Incorporating Nickel(II)-Chelate Complexes. Langmuir 2015, 31, 13048–13053; Nguyen, T. N. Studies on Mixed Chelates. VII. Mixed Nickel(II) Chelates Containing N,N′- or N,N-Dialkylethylenediamines and Acetylacetone. Bull. Chem. Soc. Jpn. 1977, 50 (1), 154–157; Wei, X. J. Vis-Spectrum Investigation of Thermo-Solvatochromic Behaviors of a Mixed Diamine and β-Diketonate Ligand Ni(II) Complex in Different Alcoholic Solutions. Acta Phys.-Chim. Sin. 2009, 25 (7), 1449–1454; Inorganic and Analytical Chemistry Experiment Test of The 10th Chinese National Undergraduate Chemistry Laboratory Tournament https://chemlabs.nju.edu.cn/DFS/file/2019/08/26/20190826132901247mmvyr5.pdf?iid=2382 (accessed November 2023).), which using a large amount of organic solvents, the aqueous and solid phase synthesis methods described here are remarkably green, environmentally friendly, high efficiency and highly reproducible, and the complex [Ni(Me₃en)(acac)]BPh₄ showing a remarkable reversible solvatochromic phenomenon, so this experiment is very suitable as a classroom demonstration for first-year undergraduates in inorganic chemistry or general chemistry. By performing this experiment, students will gain experience in solid phase synthesis, purification, and UV–vis characterization of the complex. In addition, students will gain appreciation of how solvatochromism and thermochromism (in acetone) of the complex Ni(Me₃en)(acac)]BPh₄ and their mechanisms, and progress in the understanding of the effect of the configuration of a complex on crystal field splitting, and the effect of crystal field splitting on color.