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M. Arakawa-Itoh, M. Shibata, W. Linert, Y. Fukuda:
"Steric Crowding Effect of 1,3-Diketonates on the Structures and the Solution Behaviors of Nickel(II) Mixed-Ligand Complexes";
Bulletin of the Chemical Society of Japan, 83 (2010), 7; 790 - 798.

Seven nickel(II) mixed-ligand complexes were synthesized: Ni(dike)(diam)X, where dike is a 1,3-diketonate such as 3,5-heptanedionate (dedk) or 2,6-dimethyl-3,5-heptanedionate (dmhd), diam is an N-alkylated ethylenediamine such as N,N,N¤,N¤-tetramethylethylenediamine (tmen) or 1,2-dipiperidinoethane (dipe), and X is BPh41 or NO31. The crystal structures were analyzed: each nitrate complex has a six-coordinated octahedral structure with a bidentate-coordinated nitrate, and each tetraphenylborate complex has a four-coordinated square-planar structure. The ligand field strength of [Ni(dike)(diam)]BPh4 in the solid state increases in the order: [Ni(dmhd)(dipe)]BPh4 < [Ni(dedk)(dipe)]BPh4 < [Ni(dmhd)(tmen)]BPh4 = [Ni(dedk)(tmen)]BPh4. In solution, the change of the color depending on the donor/acceptor ability of the solvent, i.e., solvatochromism was observed. When dimethyl sulfoxide was added to a solution of [Ni(dike)(diam)]BPh4 in inert 1,2-dichloroethane, the adduct formation constants are in the order: [Ni(dmhd)(dipe)]- BPh4 < [Ni(dedk)(dipe)]BPh4 1 [Ni(dmhd)(tmen)]BPh4 = [Ni(dedk)(tmen)]BPh4, reflecting the difference in steric hindrance of the ligands rather than the difference in ligand field strength. The steric crowding effect of 1,3-diketonates was observed in the solid state and solution when bulky dipe is used as diamine.

coordination Chemistry, Solvatochromism, Chromotropism

http://dx.doi.org/10.1246/bcsj.20090322