title: Simplest homoleptic metal-centered tetrahedrons, [M(OH2)4]2+, in 1-ethyl-3-methylimidazolium tetrafluoroborate ionic liquid (M = Co, Ni, Cu).
abstract: Dissolution of a tetrafluoroborate or perchlorate salt of [M(OH(2))(6)](2+) (M = Co, Ni, Cu) in 1-ethyl-3-methylimidazolium tetraluforoborate ionic liquid ([emim]BF(4)) results in significant solvatochromism and increasing intensity of color. These observations arise from partial dehydration from the octahedral [M(OH(2))(6)](2+) and formation of the tetrahedral [M(OH(2))(4)](2+). This reaction was monitored by the intense absorption band due to the d-d transition in the UV-vis absorption spectrum. The EXAFS investigation clarified the coordination structures around M(2+) {[Co(OH(2))(4)](2+), R(Co-O) = 2.17 Å, N = 4.2; [Cu(OH(2))(4)](2+), R(Cu-O) = 2.09 Å, N = 3.8}. (1)H and (19)F NMR study suggested that both [emim](+) and BF(4)(-) are randomly arranged in the second-coordination sphere of [M(OH(2))(4)](2+).
authors.affiliation: Department of Materials and Life Science, Seikei Univeristy, 3-3-1 Kichijoji-kitamachi, Musashino-shi 180-8633 Tokyo, Japan. k.takao@st.seikei.ac.jp
authors.forename: Koichiro
authors.initials: K
authors.lastname: Takao
authors.forename: Yurina
authors.initials: Y
authors.lastname: Tone
authors.forename: Christoph
authors.initials: C
authors.lastname: Hennig
authors.forename: Shohei
authors.initials: S
authors.lastname: Inoue
authors.forename: Taro
authors.initials: T
authors.lastname: Tsubomura