Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439, United States.
Inorg Chem. 2012 Feb 20;51(4):2121-9. doi: 10.1021/ic201924q. Epub 2012 Feb 1.
The structural and magnetic properties of the newly crystallized CuX(2)(pyzO)(H(2)O)(2) (X = Cl, Br; pyzO = pyrazine-N,N'-dioxide) coordination polymers are reported. These isostructural compounds crystallize in the monoclinic space group C2/c with, at 150 K, a = 17.0515(7) Å, b = 5.5560(2) Å, c = 10.4254(5) Å, β = 115.400(2)°, and V = 892.21(7) Å(3) for X = Cl and a = 17.3457(8) Å, b = 5.6766(3) Å, c = 10.6979(5) Å, β = 115.593(2)°, and V = 950.01(8) Å(3) for X = Br. Their crystal structure is characterized by one-dimensional chains of Cu(2+) ions linked through bidentate pyzO ligands. These chains are joined together through OH···O hydrogen bonds between the water ligands and pyzO oxygen atoms and Cu-X···X-Cu contacts. Bulk magnetic susceptibility measurements at ambient pressure show a broad maximum at 7 (Cl) and 28 K (Br) that is indicative of short-range magnetic correlations. The dominant spin exchange is the Cu-X···X-Cu supersuperexchange because the magnetic orbital of the Cu(2+) ion is contained in the CuX(2)(H(2)O)(2) plane and the X···X contact distances are short. The magnetic data were fitted to a Heisenberg 1D uniform antiferromagnetic chain model with J(1D)/k(B) = -11.1(1) (Cl) and -45.9(1) K (Br). Magnetization saturates at fields of 16.1(3) (Cl) and 66.7(5) T (Br), from which J(1D) is determined to be -11.5(2) (Cl) and -46.4(5) K (Br). For the Br analog the pressure dependence of the magnetic susceptibility indicates a gradual increase in the magnitude of J(1D)/k(B) up to -51.2 K at 0.84 GPa, suggesting a shortening of the Br···Br contact distance under pressure. At higher pressure X-ray powder diffraction data indicates a structural phase transition at ∼3.5 GPa. Muon-spin relaxation measurements indicate that CuCl(2)(pyzO)(H(2)O)(2) is magnetically ordered with T(N) = 1.06(1) K, while the signature for long-range magnetic order in CuBr(2)(pyzO)(H(2)O)(2) was much less definitive down to 0.26 K. The results for the CuX(2)(pyzO)(H(2)O)(2) complexes are compared to the related CuX(2)(pyrazine) materials.
新结晶的 CuX(2)(pyzO)(H(2)O)(2)（X = Cl，Br；pyzO = 吡嗪-N，N'-二氧化物）配位聚合物的结构和磁性性质。这些等结构的化合物在 150 K 下结晶为单斜晶系 C2/c 空间群，a = 17.0515(7) Å，b = 5.5560(2) Å，c = 10.4254(5) Å，β = 115.400(2)°，V = 892.21(7) Å(3)，X = Cl 和 a = 17.3457(8) Å，b = 5.6766(3) Å，c = 10.6979(5) Å，β = 115.593(2)°，V = 950.01(8) Å(3)，X = Br。它们的晶体结构的特点是通过桥联双齿 pyzO 配体连接的一维 Cu(2+)离子链。这些链通过 OH···O 氢键和 Cu-X···X-Cu 接触连接在一起，氢键存在于水配体和 pyzO 氧原子之间。在环境压力下的 bulk 磁化率测量显示在 7（Cl）和 28 K（Br）处出现宽最大值，这表明存在短程磁关联。主要的自旋交换是 Cu-X···X-Cu 超交换，因为 Cu(2+)离子的磁轨道包含在 CuX(2)(H(2)O)(2)平面内，并且 X···X 接触距离很短。磁性数据拟合到 Heisenberg 1D 均匀反铁磁链模型，J(1D)/k(B) = -11.1(1)（Cl）和 -45.9(1) K（Br）。在 16.1(3)（Cl）和 66.7(5) T（Br）的磁场下饱和磁化，从中确定 J(1D)为 -11.5(2)（Cl）和 -46.4(5) K（Br）。对于 Br 类似物，磁化率随压力的变化表明，在 0.84 GPa 下，J(1D)/k(B)逐渐增加到 -51.2 K，这表明在压力下 Br···Br 接触距离缩短。在更高的压力下，X 射线粉末衍射数据表明在约 3.5 GPa 处发生结构相变。μ子自旋弛豫测量表明 CuCl(2)(pyzO)(H(2)O)(2)是有序的，T(N) = 1.06(1) K，而 CuBr(2)(pyzO)(H(2)O)(2)中长程磁有序的特征则不那么明确，直至 0.26 K。CuX(2)(pyzO)(H(2)O)(2)配合物的结果与相关的 CuX(2)(吡嗪)材料进行了比较。
