Copper(II) Carboxylates with 2,3,4-Trimethoxybenzoate and 2,4,6-Trimethoxybenzoate: Dinuclear Cu(II) Cluster and µ-Aqua-Bridged Cu(II) Chain Molecule

Abstract

Copper(II) complexes with 2,3,4-trimethoxybenzoic acid (H234-tmbz) and 2,4,6-trimethoxybenzoic acid (H246-tmbz), [Cu2(234-tmbz)4(H2O)2] (6) and [Cu(246-tmbz)2(µ-H2O)2(H2O)2]n (7), were synthesized and characterized by elemental analysis, infrared and UV-vis spectra and temperature dependence of magnetic susceptibilities (1.9–300 K). The X-ray crystal structures revealed that the former 6 is a dinuclear cluster having syn-syn-bridged Cu2(µ-234-tmbz)4 core with Cu···Cu separation of 2.6009(7) Å, while the latter 7 is a µ-aqua-bridged chain molecule consisting of Cu(246-tmb)2(µ-H2O)2(H2O)2 units with Cu···Cu separation of 4.1420(5) Å. Temperature dependence of magnetic susceptibilities showed that an antiferromagnetic interaction with 2J = −272 cm−1 for 6 and a weak antiferromagnetic interaction with J = −0.21 cm−1 for 7, between the two copper(II) ions. The adsorption isotherm of 6 showed Types I behavior having a 125.4 m2g−1 of specific surface area.

Crystal Structure of Tetrakis(μ-2,3,6-trimethoxybenzoato-κ<i>O</i>:κ<i>O</i>′)bis[(methanol)copper(II)]: Largely Rotated Benzoate Ring to the Carboxylato Bridge

“…3, is 74.9(2) (or 44.6(3) ). In the present complex, the rotation angles, frot, are much larger among the dinuclear copper(II) benzoate analogues, except for the μ-aqua-bridged 1D polynuclear complex [Cu(246-tmbz)2(μ-H2O)(H2O)2]n, although the bending angles, fbend, are comparable to those of the related copper(II) benzoate derivatives, [9][10][11][12] listed in Table 3, and those of other copper(II) benzoates [fbend = 1.5(4) -11.4(3) and frot = 5.3(4) -19.5 (8) ]. 1 The large rotation of the benzoate rings was observed for only the cases involving the dinuclear complex [Cu2(236-tmbz)4(CH3OH)2] and the 1D polynuclear complex [Cu(246-tmbz)2(μ-H2O)(H2O)2]n, 11 suggesting that the presence of the 2-and 6-methoxy groups of the benzoate ring may induce a large deviation from coplanarity with the adjacent carboxy group, possibly because of an electrostatic repulsion between the methoxy-oxygen and the carboxy-oxygen atoms.…”

“…Dinuclear copper(II) carboxylates have received much attention by many inorganic chemists in a related development with functional materials because of the unique paddle-wheel clusters. [1][2][3][4][5][6][7][8][9][10][11][12] We recently reported on dinuclear copper(II) benzoate analogues, which have a syn-syn-bridged dinuclear cluster with four benzoate rings attached to three methoxy or benzyloxy groups. [9][10][11][12] Interestingly, one of these compounds exhibited a high adsorption property for N2, like in the case of a 1D coordination polymer of an alternated chain of dinuclear copper(II) benzoate and pyrazine.…”

“…[1][2][3][4][5][6][7][8][9][10][11][12] We recently reported on dinuclear copper(II) benzoate analogues, which have a syn-syn-bridged dinuclear cluster with four benzoate rings attached to three methoxy or benzyloxy groups. [9][10][11][12] Interestingly, one of these compounds exhibited a high adsorption property for N2, like in the case of a 1D coordination polymer of an alternated chain of dinuclear copper(II) benzoate and pyrazine. 5,6,11 We also found that a μ-aqua-bridged 1D coordination polymer, 2(μ-H2O)(H2O)2]n, formed instead of a dinuclear cluster in the case of 2,4,6-trimethoxybenzoate (246-tmbz -) due to a steric hindrance of the 2,6-positioned methoxy groups.…”

“…[9][10][11][12] Interestingly, one of these compounds exhibited a high adsorption property for N2, like in the case of a 1D coordination polymer of an alternated chain of dinuclear copper(II) benzoate and pyrazine. 5,6,11 We also found that a μ-aqua-bridged 1D coordination polymer, 2(μ-H2O)(H2O)2]n, formed instead of a dinuclear cluster in the case of 2,4,6-trimethoxybenzoate (246-tmbz -) due to a steric hindrance of the 2,6-positioned methoxy groups. 11 In this paper, we focused on the molecular structure of copper(II) carboxylate with 2,3,6-trimethoxybenzoate (236-tmbz -) to see whether the 236-tmbzligand constitutes a similar dinuclear cluster or not, and determined the crystal structure of the isolated complex, which has the molecular structure shown in Fig.…”

“…The benzoate bridging moieties are not coplanar, as found in the related dinuclear copper(II) benzoates. 1,[9][10][11][12] The dihedral angle between the O1-C7-O2 (or O6-C17-O7) and Cu1-O1•••O2-Cu1′ (or Cu1-O6•••O7-Cu1′) planes, which denotes the bending angle (fbend) 1 of the carboxylato OCO plane in the carboxylato-bridge, is 7.1(5) (or 7.0(3) ). On the other hand, the dihedral angle between the O1-C7-O2 (or O6-C17-O7) and C1-C2-C3-C4-C5-C6 (or C11-C12-C13-C14-C15-C16) planes, which denotes the rotation angle (frot) 1 of the benzoate ring relative to the OCO plane, as depicted in Fig.…”