INQUIMAE-DQIAQF, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria, C1428EHA, Buenos Aires, Argentina.
Inorg Chem. 2010 Jan 18;49(2):695-703. doi: 10.1021/ic902005m.
An anhydrous copper carboxylate compound of formula Cu(trans-2-butenoate)(2) has been characterized. X-ray analysis reveals a structure built by paddlewheel units bridged by pairs of Cu...O axial bonds to give infinite chains arranged in a new topological motif. Susceptibility measurements in the 10-300 K temperature range, and isothermal magnetization curves at 2, 5, 10, and 50 K with fields up to 5 T, were obtained. Electron Paramagnetic Resonance (EPR) spectra of powder samples were measured at 33.9 GHz at 300 K, and at 9.60 GHz at temperatures in the range 90 <or= T <or= 350 K. Fitting the susceptibility data to a chain model of alternating paddlewheel and [Cu(mu-O)(2)Cu] dinuclear units yielded exchange interactions J(1) = -330.6(1) cm(-1) and J(2) = 5.9(2) cm(-1). The EPR spectra reflect the usual antiferromagnetic dinuclear behavior, with zero field splitting parameters of the excited spin triplet, D = -0.329(3) cm(-1) and E approximately 0, plus a central peak not expected for isolated dinuclear units. We interpret this peak as arising from the stochastic spin dynamics of the chain introduced by exchange couplings between spins in neighbor dinuclear units, which averages out the zero field splitting. Interactions of the units with the rest of the chain acting as a spin bath give rise to a quantum transition between localized dinuclear states and states of the spin chain. This effect competes with the condensation of the antiferromagnetic dinuclear units into the singlet ground state, producing a characteristic temperature dependence of the shape of the powder EPR spectra. We interpret these features in terms of basic theories of magnetic resonance in coupled spin systems applied to the chain array of dinuclear units.
一种无水铜羧酸盐化合物的化学式为[Cu(trans-2-丁烯酸酯)(2)]（n），已经被表征。X 射线分析揭示了一个由桨轮单元通过 Cu...O 轴向键对连接而成的结构，这些键对将无限链排列成一种新的拓扑结构。在 10-300 K 温度范围内进行了磁化率测量，并在 2、5、10 和 50 K 下获得了高达 5 T 的等温磁化曲线。在 300 K 下用 33.9 GHz 测量了粉末样品的电子顺磁共振（EPR）谱，在 90 <= T <= 350 K 的温度范围内用 9.60 GHz 测量了 EPR 谱。将磁化率数据拟合到交替桨轮和[Cu(mu-O)(2)Cu]双核单元的链模型，得到交换相互作用 J(1) = -330.6(1) cm(-1)和 J(2) = 5.9(2) cm(-1)。EPR 谱反映了通常的反铁磁双核行为，激发三重态的零场分裂参数为 D = -0.329(3) cm(-1)和 E 约为 0，外加一个不期望孤立双核单元出现的中心峰。我们将这个峰解释为源于相邻双核单元之间的交换耦合引起的链的随机自旋动力学，这种耦合平均了零场分裂。单元与链的其余部分的相互作用作为自旋浴，导致双核态和自旋链态之间的量子跃迁。这种效应与反铁磁双核单元凝聚成单重基态竞争，导致粉末 EPR 谱形状的特征温度依赖性。我们根据应用于双核单元链阵列的耦合自旋系统的基本磁共振理论来解释这些特征。
