Dinuclear Copper(II) 3,4,5-Tri-O-benzylgallate
Masahiro Mikuriya1, *, Chihiro Yamakawa1, Naoyuki Masuda1, Daisuke Yoshioka1, Sayuri Yamaguchi2, Hidetoshi Yamada2, Tsutomu Mizuta3, Naomi Kawata4, Hidekazu Tanaka5, Makoto Handa5
Ellagitannins have attracted much attention because of the biological and pharmacological activities. In the total synthesis of ellagitannins, 3,4,5-tri-O-benzylgallic acid has been a key compound to introduce the protected galloyl group. From the perspective of coordination chemis-try, 3,4,5-tri-O-benzylgallic acid is an interesting carboxylate ligand which might be capable of dinucle-ar carboxylate complex. Such a dinuclear carboxylate complex might be interesting as a new example of copper acetate type complexes.
The objective of the work is to synthesize a copper acetate type complex by using 3,4,5-tri-O-benzylgallic acid and to see a new feature of copper acetate compounds, by elucidating the crystal structure, magnetic property, and adsorption property for N2 gas.
Copper(II) 3,4,5-tri-O-benzylgallate has been synthesized by a reaction of 3,4,5-tri-O-benzylgallic acid and copper(II) nitrate at pH=9 condition. The isolated complex was characterized us-ing single-crystal X-ray structure analysis, XRD analysis, UV-visible spectroscopy, IR spectroscopy, and temperature dependence of magnetic susceptibility.
The crystal structure shows a crystallographically centrosymmetric dinuclear molecule with four carboxylato-bridges and axial dimethylformamide molecules and crystal dmf molecules [Cu···Cu 2.6345(12) Å]. In the crystal, 1D supramolecular assembly by π-π interaction between the benzyl aro-matic rings of dinuclear molecules was observed. Temperature dependence of magnetic susceptibilities showed a considerable antiferromagnetic interaction between the two copper(II) ions (2J = –214 cm–1). Type-II gas-adsorption property was observed for N2.
A key-compound for the total synthesis of ellagitannins, 3,4,5-tri-O-benzylgallic acid (Htbng), was shown to be a new ligand for the synthesis of dinuclear copper acetate analogue with a lantern-type core, extending the realm of copper acetate clusters.
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