Reversible color changes of chiral double salts of d-(+)-camphoric diammonium and transition-metal sulfates via gain and loss of crystalline and coordination water molecules

Six novel chiral double salts (1–6) composed of d-(+)-camphoric diammonium (LH2) and transition-metal sulfates, formulated as {[M(SO4)2(H2O)4](LH2)}·2H2O [M = Fe(II), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II)], have been prepared and fully characterized including single-crystal X-ray diffraction, Fourier transform infrared (FT-IR) and vibrational circular dichroism (VCD) spectral investigations. Co(II), Ni(II) and Cu(II) compounds 2–4 exhibit reversible color changes between 20 and 140 °C via gain and loss of two crystalline and four coordination water molecules, which can be proved by their thermogravimetric (TG) and powder X-ray diffraction (PXRD) analyses. To the best of our knowledge, this is the first report on chiral double salts showing chromotropism properties.

Six chiral double salts (1–6), formulated as {[M(SO4)2(H2O)4](LH2)}·2H2O [M = Fe(II), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II), LH2 = d-(+)-camphoric diammonium], are prepared and characterized by single-crystal X-ray diffraction and FT-IR/VCD spectra. Co(II), Ni(II) and Cu(II) complexes (2–4) exhibit reversible color changes via gain and loss of two crystalline and four coordination water molecules, which can be proved by their TG and PXRD analyses.Figure optionsDownload as PowerPoint slideHighlights
► Six chiral double salts of d-(+)-camphoric diammonium and metal sulfates are characterized.
► FT-IR/VCD spectra are used to characterize the chirality of metal complexes.
► Co(II), Ni(II), Cu(II) compounds show reversible color changes via gain or loss of water molecules.
► This is the first report on chiral double salts exhibiting chromotropism properties.