Ligand Effects on the Structure and Magnetic Properties of Alternating Copper(II) Chains with 2,2鈥?Bipyrimidine- and Polymethyl-Substituted Pyrazolates as Bridging Ligands

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• 作者：Isabel Castro ; M. Luisa Calatayud ; Wdeson P. Barros ; Jos茅 Carranza ; Miguel Julve ; Francesc Lloret ; Nadia Marino ; Giovanni De Munno
• 刊名：Inorganic Chemistry
• 出版年：2014
• 出版时间：June 2, 2014
• 年：2014
• 卷：53
• 期：11
• 页码：5759-5771
• 全文大小：569K
• 年卷期：v.53,no.11(June 2, 2014)
• ISSN：1520-510X

文摘

A novel series of heteroleptic copper(II) compounds of formulas {[Cu₂(渭-H₂O)(渭-pz)₂(渭-bpm)(ClO₄)(H₂O)]ClO₄路2H₂O}_n (1), {[Cu₂(渭-H₂O)(渭-3-Mepz)₂(渭-bpm)](ClO₄)₂路2H₂O}_n (2), and {[Cu₂(渭-OH)(渭-3,5-Me₂pz)(渭-bpm)(H-3,5-Me₂pz)₂](ClO₄)₂}_n (3) [bpm = 2,2鈥?bipyrimidine, Hpz = pyrazole, H-3-Mepz = 3-methylpyrazole, and H-3,5-Me₂pz = 3,5-dimethylpyrazole] have been synthesized and structurally characterized by X-ray diffraction methods. The crystal structures of 1 and 2 consist of copper(II) chains with regular alternating bpm and bis(pyrazolate)(aqua) bridges, whereas that of 3 is made up of copper(II) chains with regular alternating bpm and (pyrazolate)(hydroxo) bridges. The copper centers are six- (1) or five-coordinate (2) in axially elongated, octahedral (1) or square-pyramidal (2) environments in 1 and 2, whereas they are five-coordinate in distorted trigonal-bipyramidal surroundings in 3. The values of the copper鈥揷opper separations across the bpm/pyrazolate bridges are 5.5442(7)/3.3131(6) (1), 5.538(1)/3.235(1) (2), and 5.7673(7)/3.3220(6) 脜 (3). The magnetic properties of 1鈥?b>3 have been investigated in the temperature range of 25鈥?00 K. The analysis of their magnetic susceptibility data through the isotropic Hamiltonian for an alternating antiferromagnetic copper(II) chain model [H = 鈭?i>J鈭?sub>i=1鈥?i>n/2 (S_2i路S_2i鈥? + 伪S_2i路S_2i+1), with 伪 = J鈥?J and S_i = S_Cu = 1/2] reveals the presence of a strong to moderate antiferromagnetic coupling through the bis(pyrazolate)(aqua) [鈭?i>J = 217 (1) and 215 cm^鈥? (2)] and (pyrazolate)(hydroxo) bridges [鈭?i>J = 153 cm^鈥? (3)], respectively, whereas a strong to weak antiferromagnetic coupling occurs through the bis-bidentate bpm [鈭?i>J鈥?= 211 (1), 213 (2), and 44 cm^鈥? (3)]. A simple orbital analysis of the magnetic exchange interaction within the bpm- and pyrazolate-bridged dicopper(II) fragments of 1鈥?b>3 visualizes the 蟽-type pathways involving the (dx²鈥?i>y²) (1 and 2) or d(z²) (3) magnetic orbitals on each metal ion, which account for the variation of the magnetic properties in these three novel examples of one-dimensional copper(II) compounds with regular alternating intrachain antiferromagnetic interactions.