Communication pubs.acs.org/IC
Hexanuclear Platinum(II) Thiolate Macrocyclic Host: Charge-TransferDriven Inclusion of a AgI Ion Guest Yukatsu Shichibu,*,†,‡ Keisuke Yoshida,† and Katsuaki Konishi*,†,‡ †
Graduate School of Environmental Science and ‡Faculty of Environmental Earth Science, Hokkaido University, North 10 West 5, Sapporo 060-0810, Japan S Supporting Information *
large for small-molecule inclusion such as in previous examples,3,10,14−16 we envisioned that this cavity could be used as a good metal-ion trap. Figure 1 shows a titration experiment of the macrocycle with AgI ions. A spectrum of pure 1 showed peaks at 302 and 380 nm.
ABSTRACT: The inclusion of a AgI ion by a hexanuclear platinum(II) thiolate macrocycle in solution was demonstrated, and the inclusion structure was determined by Xray crystallography. Unique host−guest intermetallic interactions driven by charge transfer were elucidated by optical absorption spectroscopy and theoretical calculations.
A
s an inorganic analogy of crown ethers, metallacrowns, i.e., metal-containing macrocycles, have received much attention, and their applications such as cation traps via O or N atoms, catalysis, and single-molecule magnet have been reported.1 Recently, as one group of metallacrowns, thiolate-bridged group 10 transition-metal macrocycles with tiara-like prismatic cages [{M(SR)2}n] (M = Ni, Pd, Pt) have attracted increasing attention because of their size diversities2−7 and photochemical properties.8−10 Because MnS2n frameworks of the macrocycles are relatively simple and rigid compared to those of other metallacrowns,11−13 exploration of their inclusion-induced properties originating in guest traps directly via cage-constituting metal atoms is of great interest. Several inclusion compounds of undeca-, deca-, and octanuclear metal thiolate macrocyclic hosts have been reported.3,10,14−16 However, guests were limited to small organic molecules, and such properties, together with the roles of constituent metal atoms in the compounds, were not well presented probably because of the lack of obvious contribution of the metals to inclusion complexations. Herein, we report the synthesis of a hexanuclear platinum(II) thiolate macrocycle, [{Pt(SC12H25)2}6] (1), containing a small cavity suited for metalion accommodation and demonstrate the inclusion of a AgI ion at the cavity in solution. Unique host−guest intermetallic interactions arising from inclusion were investigated using both experimental and theoretical methods. The platinum(II) thiolate macrocycle 1 was synthesized following a literature method for a palladium(II) thiolate macrocycle with slight modification.5 Furthermore, the singlecrystal X-ray structural analysis of 1 showed a M6S12 framework almost identical with that of the corresponding palladium macrocycle (Figure S1). Each Pt atom, accompanied by four adjacent S atoms of μ-SC12H25 ligands, can be viewed as a PtS4 square plane, and all of the six planes linked in an edge-sharing manner form a hexagonal prism. The diagonal Pt−Pt distance on average corresponding to the ring diameter was 6.342 Å (Table S3); therefore, the size of the centered cavity was estimated to be 2.84 Å from the van der Waals radius. Although this size is not so © XXXX American Chemical Society
Figure 1. UV−vis absorption spectral changes of 1 in CH2Cl2 (50 μM) during titration with 0−1 equiv of AgSbF6 in CH3CN (10 mM). The isosbestic points were observed at 285 and 340 nm. The inset shows the corresponding molar ratio plot at 477 nm. A saturated absorbance was observed at [Ag+]0/[1]0 = 1, and the titration profile shows that the association constant estimated was >107 M−1. The concentration was corrected.
With increasing amount of AgI ions, these peaks became smeared, and a broad band with a hump appeared at ∼477 nm and increased gradually, together with the color change of the solution from yellow to orange. Furthermore, an absorbance titration profile at 477 nm showed a clear inflection point at a mole ratio of [Ag+]0/[1]0 of unity (Figure 1, inset), indicating that a 1:1 stoichiometric event occurred. The monovalent species [1·Ag]+ was detected in the electrospray ionization mass spectrum of a 1:1 mixture of 1 and AgSbF6 (Figure S3), which indicates complexation of 1 with Ag+. Single-crystal X-ray analysis of [1·Ag](SbF6) clearly shows the crown ether-like inclusion compound [1⊃Ag]+ (Figures 2a and S2). The framework of Pt6S12 after inclusion was maintained with slight shrinkage in the distance (
