Department of Chemistry and Biochemistry and the Biomolecular Sciences Institute, Florida International University, Miami, FL 33199, USA.
Phys Chem Chem Phys. 2018 Jun 27;20(25):17234-17244. doi: 10.1039/c8cp02643b.
The X-ray crystal structure of the CuII complex [Cu3(μ3-OH)(μ-pz)3(PhCOO)3]- (pz- = pyrazolato anion) shows an isosceles triangular core, further forming a hexanuclear H-bonded aggregate. Cleavage of the H-bonds in solution results in isolated trinuclear species. Analysis of variable temperature magnetic susceptibility data of a powder sample shows an antiferromagnetically-coupled Cu3-core with a doublet ground state and isotropic exchange parameters (Jave = -355 cm-1, Hiso = -JijSiSj). The fitting of magnetic data requires the inclusion of antisymmetric exchange, AE (HAE = Gij·Si × Sj) with Gz = 31.2 cm-1 and no detectable inter-Cu3 isotropic exchange. X-band EPR spectroscopy in a frozen tetrahydrofuran solution of the compound indicates isolated Cu3-species with g‖,eff = 2.25, g⊥,eff = 1.67. The small value of g⊥,eff (≪2.0) is consistent with the presence of AE in agreement with the analysis of the magnetic measurements. The parallel component exhibits a hyperfine pattern corresponding to one I = 3/2 nucleus with A‖ = 425 MHz. This implies a specific exchange coupling scheme obeying the order |J12| = |J13| < |J23| consistent with the crystallographically determined two long and one short CuCu distances. The role of AE in modulating the hyperfine parameters in antiferromagnetic Cu3 clusters is studied. EPR spectra at X- and Q-band were performed with powder samples of the cluster at liquid helium temperatures. The spectra in both bands are consistent with two interacting Sa,b = 1/2 species in the point dipolar approximation. Fitting of the spectra reveals that each spin is characterized by g‖ = 2.24, g⊥ = 1.65 which is in agreement with an isolated Cu3 cluster in the ground state. The determined inter-spin distance of 4.4-4.5 Å is very close to the distance between the Cu(1) and Cu(1)' sites of the two trimeric units as imposed crystallographically (4.3 Å). This constitutes further verification of the specific exchange coupling scheme within each trimer. Magnetostructural correlations previously adopted for antiferromagnetically coupled Cu3 clusters are discussed in the light of the combined magnetic measurements and EPR spectroscopy.
X 射线晶体结构的 CuII 配合物 [Cu3(μ3-OH)(μ-pz)3(PhCOO)3]-（pz-=吡唑olate 阴离子）显示等腰三角形核心，进一步形成六核氢键聚合体。在溶液中氢键的断裂导致孤立的三核物种。对粉末样品的变温磁化率数据分析表明，Cu3 核具有反铁磁耦合的 doublet基态和各向同性交换参数（Jave = -355 cm-1，Hiso = -JijSiSj）。磁数据的拟合需要包含不对称交换，AE（HAE = Gij·Si × Sj），Gz = 31.2 cm-1，没有检测到 Cu3 之间的各向同性交换。化合物在四氢呋喃冷冻溶液中的 X 波段 EPR 光谱表明，具有 g‖，eff = 2.25，g⊥，eff = 1.67 的孤立 Cu3-物种。g⊥，eff 的小值（≪2.0）与存在 AE 一致，与磁测量分析一致。平行分量表现出与一个 I = 3/2 核对应的超精细图案，A‖ = 425 MHz。这意味着存在特定的交换耦合方案，遵循 |J12| = |J13| < |J23| 的顺序，与结晶学确定的两个长距离和一个短距离 CuCu 距离一致。研究了 AE 在调节反铁磁 Cu3 簇中超精细参数中的作用。在液氦温度下，用簇的粉末样品进行了 X-和 Q-波段的 EPR 光谱。两个波段的光谱都符合点偶极近似中的两个相互作用的 Sa，b = 1/2 种。光谱拟合表明，每个自旋的特征是 g‖ = 2.24，g⊥ = 1.65，这与基态下的孤立 Cu3 簇一致。确定的自旋间距离为 4.4-4.5 Å，非常接近两个三聚体单元的 Cu(1)和 Cu(1)'位点之间的距离（4.3 Å）。这进一步验证了每个三聚体中特定的交换耦合方案。根据综合的磁性测量和 EPR 光谱，讨论了以前用于反铁磁耦合 Cu3 簇的磁结构相关性。
