Copper(II) chelates of cyclam and dicyclohexylcyclam as solvatochromic indicators for an easy prediction of solvent parameters.

of various physicochemical and spectroscopic measurements using various indicator compounds. 1–6 Especially, three parameters, dielectric constant, DC, donor number, DN, and acceptor number, AN serve as fundamental and extensive set for applications. However, it is not easy to directly derive these parameters by means of the original measurement method. It is expected that they can be predicted by easy means such as a UV/Vis spectroscopic measurement. UV/Vis spectroscopic measurements using solvatochromic chelate compounds, such as diamine-β-diketone Cu(II) and 1,4,8,11-tetramethylcyclam Ni(II), are used to derive some solvent parameters based on a correlation between the solvent-solute interaction and the solvent polarity. 7,8 In a previous report, we discussed the complexations and solvatochromic behaviors of macrocyclic as shown in Formula. Their solvatochromic shifts on the visible absorption spectra were measured in water and some typical organic solvents, namely propylenecarbonate (PC), acetone (AC), methanol (MeOH), formamide (FA), N,N-dimethylformamide (DMF), dimethylsulfoxide (DMSO) and acetonitrile (AcCN). Their maximum absorption wavenumbers for the solvatochromic spectra shift depended on three fundamental solvent parameters, such as DC, AN and DN. 9–11 Their solvatochromic shifts change moderately and continuously depending on the solvent characters from D4h to axial-elongated D4h by a solvent-solute interaction without any essential change from square-planar to octahedral or square-pyramidal geometry, as observed in Ni(II) chelates. 10 In this work, by applying the Cu(II) chelates of 1, 2 and 3 as the solvatochromic indicators for the easy prediction of solvent parameters, we tried to collect a set of three fundamental parameters for some organic solvents with one or two unknowns among them. Experimental The Cu(II) chelates of cyclam (1) and dicyclohexylcyclam (2, 3) were prepared as the perchlorate, [Cu(L)](ClO4)2, in the same manner as previous reports. 9,10 These chelates are hereinafter described as chelates 1, 2 and 3. Commercial GR-grade, Dotite Spectro-sol and Wako GR reagents were used for organic solvents without any further purification. The UV-Vis spectra were measured with a Hitachi U-2000 double-beam spectrophotometer at 25˚C. The solvatochromic shifts of the Cu(II) chelates of 1, 2 and 3 are assumed to be caused by a perturbation of an axially-elongated ligand field through an axial approach of the solvent to the cyclam ring with D4h symmetry. 10 This is well known to be a pentaammine effect. 12,13 The stronger is the axial interaction between the chelate and the solvent, the lower are the maximum absorption wave number (i.e. red-shift). The interaction effect is closely correlated with …