Institut Parisien de Chimie Moléculaire, UPMC Univ Paris 06, Paris, 75252, France.
Chemistry. 2010 Nov 15;16(43):12838-51. doi: 10.1002/chem.201001737.
Double-stranded copper(II) string complexes of varying nuclearity, from di- to tetranuclear species, have been prepared by the Cu(II)-mediated self-assembly of a novel family of linear homo- and heteropolytopic ligands that contain two outer oxamato and either zero (1 b), one (2 b), or two (3 b) inner oxamidato donor groups separated by rigid 2-methyl-1,3-phenylene spacers. The X-ray crystal structures of these Cu(II) (n) complexes (n=2 (1 d), 3 (2 d), and 4 (3 d)) show a linear array of metal atoms with an overall twisted coordination geometry for both the outer CuN(2)O(2) and inner CuN(4) chromophores. Two such nonplanar all-syn bridging ligands 1 b-3 b in an anti arrangement clamp around the metal centers with alternating M and P helical chiralities to afford an overall double meso-helicate-type architecture for 1 d-3 d. Variable-temperature (2.0-300 K) magnetic susceptibility and variable-field (0-5.0 T) magnetization measurements for 1 d-3 d show the occurrence of S=nS(Cu) (n=2-4) high-spin ground states that arise from the moderate ferromagnetic coupling between the unpaired electrons of the linearly disposed Cu(II) ions (S(Cu)=1/2) through the two anti m-phenylenediamidate-type bridges (J values in the range of +15.0 to 16.8 cm(-1)). Density functional theory (DFT) calculations for 1 d-3 d evidence a sign alternation of the spin density in the meta-substituted phenylene spacers in agreement with a spin polarization exchange mechanism along the linear metal array with overall intermetallic distances between terminal metal centers in the range of 0.7-2.2 nm. Cyclic voltammetry (CV) and rotating-disk electrode (RDE) electrochemical measurements for 1 d-3 d show several reversible or quasireversible one- or two-electron steps that involve the consecutive metal-centered oxidation of the inner and outer Cu(II) ions (S(Cu)=1/2) to diamagnetic Cu(III) ones (S(Cu)=0) at relatively low formal potentials (E values in the range of +0.14 to 0.25 V and of +0.43 to 0.67 V vs. SCE, respectively). Further developments may be envisaged for this family of oligo-m-phenyleneoxalamide copper(II) double mesocates as electroswitchable ferromagnetic 'metal-organic wires' (MOWs) on the basis of their unique ferromagnetic and multicenter redox behaviors.
通过铜（II）介导的新型线性同多和杂多齿配体的自组装，制备了具有不同核数的双链铜（II）字符串配合物，从双核物种到四核物种，这些配体含有两个外氧肟酸和零（1b）、一个（2b）或两个（3b）内氧亚氨基供体基团，由刚性 2-甲基-1,3-亚苯基间隔物隔开。这些 Cu(II)（n）配合物（n=2（1d）、3（2d）和 4（3d））的 X 射线晶体结构显示出金属原子的线性排列，具有外 CuN（2）O（2）和内 CuN（4）发色团的整体扭曲配位几何形状。两个这样的非平面全顺式桥联配体 1b-3b 以反式排列围绕金属中心夹住，交替具有 M 和 P 螺旋手性，为 1d-3d 提供整体双介孔螺旋型结构。1d-3d 的变温（2.0-300 K）磁化率和变场（0-5.0 T）磁化测量表明，存在 S=nS(Cu)（n=2-4）高自旋基态，这是由于通过两个反式 m-亚苯基二胺型桥（J 值在+15.0 至 16.8 cm(-1)范围内）线性排列的 Cu(II)离子（S(Cu)=1/2）的未配对电子之间的中等铁磁耦合产生的。1d-3d 的密度泛函理论（DFT）计算表明，取代的亚苯基间隔物中的自旋密度符号交替，与沿线性金属阵列的自旋极化交换机制一致，终端金属中心之间的整体金属间距离在 0.7-2.2nm 范围内。1d-3d 的循环伏安法（CV）和旋转圆盘电极（RDE）电化学测量显示了几个可逆或准可逆的单电子或双电子步骤，涉及内和外 Cu(II)离子（S(Cu)=1/2）的连续金属中心氧化为顺磁性 Cu(III)离子（S(Cu)=0），在相对低的形式电位（E 值在+0.14 至+0.25 V 和+0.43 至 0.67 V 与 SCE 相比，分别）。基于其独特的铁磁和多中心氧化还原行为，可以设想将这种寡聚 m-亚苯基氧肟酸铜（II）双介孔酸盐作为电开关铁磁“金属有机线”（MOW）进一步发展。
