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Binding Properties of Solvatochromic Indicators [Cu(X)(acac)(tmen)] (X = PF6 and BF4, acac = Acetylacetonate, tmen = N,N,N′,N′-Tetramethylethylenediamine) in Solution and the Solid State

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posted on 2008-08-18, 00:00 authored by Shin-ichiro Noro, Nobuhiro Yanai, Susumu Kitagawa, Tomoyuki Akutagawa, Takayoshi Nakamura
The solvatochromic indicator [Cu(acac)(tmen)(H2O)]·PF6 (1·H2O) has been synthesized and crystallographically characterized. 1·H2O binds an H2O molecule at the Cu(II) axial site, while the PF6 anion is coordination free. The binding properties of [Cu(PF6)(acac)(tmen)] (1) and [Cu(BF4)(acac)(tmen)] (2) have been investigated in solution and the solid state. The donor number of the PF6 anion (DNPF6) was determined from the UV−vis spectra of 1 in 1,2-dichloroethane. The value of DNPF6 of the PF6 anion is slightly larger than that of the tetraphenylborate anion (BPh4), which is known as a noncoordinating anion. In the solid state, 1 and 2 reversibly bind and release H2O molecules at the Cu(II) axial sites. The coordinated H2O molecules in 2 are more easily removed than those in 1 because of the strong Lewis basicity of the BF4 anion compared to the PF6 ion. The lower melting point of 1 versus 2 is attributed to the loose binding of the PF6 anions to the Cu(II) centers, which induces the dynamic nature of the crystal.

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