Preparation and Crystal Structure of Tetrakis(μ-2,4,5-trimethoxybenzoato-κO:κO′)bis[(methanol)copper(II)]-N,N-dimethylformamide (1/2) in Relation to Adsorption Property for N2

Dinuclear metal carboxylates have attracted considerable attention due to their potential application for functional materials, such as gas storage,1–4 as well as their unique structures and magnetic properties.5–12 Recently, we reported on the dinuclear copper(II) carboxylate obtained from the reaction of 3,4,5-trimethoxybenzoic acid (H345-tmbz) and copper(II) salt, [Cu2(345-tmbz)4(CH3OH)2]·2dmf (1), which has a syn-synbridged dinuclear cluster with a Cu–Cu distance of 2.6190(6)Å.11 We also synthesized the dinuclear cluster [Cu2(tbng)4(dmf )2] (tbng– = 3,4,5-tri-O-benzylgallate) (2).12 Unfortunately, these complexes did not show a good adsorption property for N2. In this work, we have employed 2,4,5-trimethoxybenzoic acid (H245-tmbz) as a carboxylic acid by changing the methoxysubstituent position to obtain a new copper(II) carboxylate, and determined the crystal structure of the isolated complex (3), which has the molecular structure as shown in Fig. 1. Copper(II) carboxylate (3) was prepared by a method described in the literature.11,12 A portion of 2,4,5-trimethoxybenzoic acid (0.5020 g, 2.366 mmol) was added to a 5 cm3 of a 0.10 M sodium hydroxide solution. The solution was neutralized by the addition of nitric acid with a phenolphthalein indicator. To this solution, a 5 cm3 of aqueous solution of copper(II) nitrate trihydrate (0.3046 g, 1.261 mmol) was added with stirring to give a pale-blue precipitate. The precipitate was collected and dried under a vacuum. Yield, 0.5008 g (82.4%). Anal. Found: C, 45.42; H, 4.46%. Calcd for C40H54Cu2O25 ([Cu2(245-tmbz)4(H2O)2]·3H2O): C, 45.24; H, 5.12%. IR (KBr, cm–1): 3581 (νOH). 3511 (νOH), 3445 (νOH), 2946 (νasCH3), 2835 (νsCH3), 1606 (νasCOO), 1462 (νsCOO). Diffuse reflectance spectra: λmax 234, 320br, 370sh, 710br nm. Adsorption measurement for N2 was performed by a MicrotracBEL BELSORP-mini II. Prior to an adsorption, the sample was evacuated at 298 K for 2 h. X-ray quality crystals were grown by recrystallization from dmf-methanol. X-ray diffraction data for the crystal were collected at 90 K on a Bruker CCD X-ray diffractometer (SMART APEX) using graphite-monochromated Mo-Kα 2021 © The Japan Society for Analytical Chemistry