Institut Lavoisier de Versailles, UMR CNRS 8180, Université de Versailles Saint Quentin, 78035 Versailles Cedex, France.
Inorg Chem. 2010 Mar 15;49(6):2851-8. doi: 10.1021/ic902341w.
The asymmetric Cr(III) polyoxometalate complex Cs(10)[(gamma-SiW(10)O(36))(2)(Cr(OH)(H(2)O))(3)] x 17 H(2)O (1) has been synthesized in water under atmospheric pressure from the trinuclear precursor [Cr(3)(CH(3)COO)(7)(OH)(2)] and the divacant ligand gamma-SiW(10)O(36). Complex 1 is built up of two gamma-SiW(10)O(36) Keggin units sandwiching a trinuclear {(Cr(III)(OH)(H(2)O))(3)} fragment where the paramagnetic centers are bridged by three mu-OH ligands forming a nearly isosceles triangle. The magnetic properties of this spin-frustrated system have thus been interpreted considering a 2-J Hamiltonian showing that the Cr(III) ions are antiferromagnetically coupled and that 1 possesses an S = 3/2 ground state with an S = 1/2 first excited state located at 11 cm(-1). These results have been confirmed by EPR spectroscopy measurements (Q-band), which have also enabled the quantification of the electronic parameters characterizing the quadruplet spin ground state. The magnitude of the magnetic exchange interactions and the nature of the ground state are discussed in light of previously reported isosceles triangular S = 3/2 clusters. UV-visible and electrochemical studies have shown that 1 is stable in aqueous media in a 1-7 pH range. This stability is chemically confirmed by the study of the reactivity of 1 with La(III) cations, which has allowed the isolation of the Cs(4)[(gamma-SiW(10)O(36))(2)(Cr(OH)(H(2)O))(3)(La(H(2)O)(7))(2)] x 20 H(2)O compound (2). Indeed, during the synthetic process of this 3d-4f system, the integrity of the (gamma-SiW(10)O(36))(2)(Cr(OH)(H(2)O))(3) building unit constituting 1 is maintained despite the high oxophilic character of the La(III) ions. The single crystal X-ray diffraction study of 2 has revealed that in the solid state the rare earth cations connect these subunits, affording a 3d-4f double-chain monodimensional system.
在大气压力下，用水从三核前体[Cr(3)(CH(3)COO)(7)(OH)(2)]和缺位配体gamma-SiW(10)O(36)合成了不对称的 Cr(III)多金属氧酸盐配合物 Cs(10)[(gamma-SiW(10)O(36))(2)(Cr(OH)(H(2)O))(3)] x 17 H(2)O(1)。配合物 1 由两个gamma-SiW(10)O(36)Keggin 单元夹在一个三聚体{(Cr(III)(OH)(H(2)O))(3)}片段之间，其中顺磁中心通过三个 mu-OH 配体桥接，形成一个近等腰三角形。因此，通过考虑 2-J 哈密顿量来解释这个自旋受挫系统的磁性，表明 Cr(III)离子是反铁磁耦合的，并且 1 具有 S = 3/2 的基态，具有位于 11 cm(-1)处的 S = 1/2 的第一激发态。这些结果通过 EPR 光谱测量(Q 波段)得到了证实，该测量还能够量化表征四重态基态的电子参数。在与之前报道的等腰三角形 S = 3/2 簇的对比中，讨论了磁交换相互作用的大小和基态的性质。UV-可见和电化学研究表明，1 在 1-7 pH 范围内的水溶液中是稳定的。通过研究 1 与 La(III)阳离子的反应，证实了这种稳定性，这使得能够分离出 Cs(4)[(gamma-SiW(10)O(36))(2)(Cr(OH)(H(2)O))(3)(La(H(2)O)(7))(2)] x 20 H(2)O 化合物(2)。事实上，在这个 3d-4f 系统的合成过程中，尽管 La(III)离子具有高亲氧性，但构成 1 的(gamma-SiW(10)O(36))(2)(Cr(OH)(H(2)O))(3)构建单元的完整性得以保持。对 2 的单晶 X 射线衍射研究表明，在固态中，稀土阳离子连接这些亚基，形成 3d-4f 双链一维系统。
