Two-dimensional correlation spectroscopic studies on coordination between organic ligands and Ni 2+ ions.

3 A2g →3 T1g (P) transition band of Ni2+ is used to probe the coordination of Ni2+ . Two-dimensional asynchronous spectra (2DCOS) are generated using the Double Asynchronous Orthogonal Sample Design (DAOSD), Asynchronous Spectrum with Auxiliary Peaks (ASAP) and Two-Trace Two-Dimensional (2T2D) approaches. Cross peaks relevant to the 3 A2g →3 T1g (P) transition band of Ni2+ are utilized to probe coordination between Ni2+ and various ligands. We studied the spectral behavior of the 3 A2g →3 T1g (P) transition band when Ni2+ is coordinated with ethylenediaminetetraacetic acid disodium salt (EDTA). The pattern of cross peaks in 2D asynchronous spectrum demonstrates that coordination brings about significant blue shift of the band. In addition, the absorptivity of the band increases remarkably. The interaction between Ni2+ and galactitol is also investigated. Although no clearly observable change is found on the 3 A2g →3 T1g (P) transition band when galactitol is introduced, the appearance of cross peak in 2D asynchronous spectrum demonstrates that coordination indeed occurs between Ni2+ and galactitol. Furthermore, the pattern of cross peak indicates that peak position, bandwidth and absorptivity of the 3 A2g →3 T1g (P) transition band of Ni(galactitol)x 2+ is considerably different from those of Ni(H2 O)6 2+ . Thus, 2DCOS is helpful to reveal subtle spectral variation, which might be helpful in shedding light on the physical-chemical nature of coordination.