Clausen H F, Overgaard J, Chen Y S, Iversen B B
Centre for Energy Materials, Department of Chemistry, and iNANO, University of Aarhus, DK-8000 Aarhus C, Denmark.
J Am Chem Soc. 2008 Jun 25;130(25):7988-96. doi: 10.1021/ja8007215. Epub 2008 May 31.
The charge density (CD) of coordination polymer Co3(C8H4O4)4(C4H12N)2(C5H11NO)3 (1) has been determined from multipole modeling of structure factors obtained from single-crystal synchrotron X-ray diffraction measurements at 16 K. The crystal structure formally contains a negatively charged framework with cations and neutral molecules in the voids. However, the CD suggests that the framework is close to neutral, and therefore qualitative conclusions based on formal charge counting, e.g., about guest inclusion properties, will be incorrect. There are considerable differences in the charge distributions of the three unique benzenedicarboxylic acid linkers, which are widely used in coordination polymers. This suggests that the electrostatic properties of coordination polymer cavities, and thereby their inclusion properties, are highly tunable. The electron density topology shows that the tetrahedrally coordinated Co atom has an atomic volume which is 15% larger than that of the octahedrally coordinated Co atom. The crystal structure has both ferromagnetic and antiferromagnetic interactions, but no direct metal-metal bonding is evidenced in the CD. The magnetic ordering therefore takes place through superexchange in the oxygen bridges and the aromatic linkers. Bonding analysis of the experimental CD reveals that two oxygen atoms, O(1) and O(11), have significant covalent contributions to the metal-ligand bonding, whereas all other oxygen atoms have closed-shell interactions with the metals. This indicates that these two oxygen atoms are the key mediators of the magnetic ordering.
通过在16K下进行的单晶同步加速器X射线衍射测量获得的结构因子的多极建模，确定了配位聚合物Co3(C8H4O4)4(C4H12N)2(C5H11NO)3(1)的电荷密度(CD)。晶体结构形式上包含一个带负电荷的骨架，空隙中有阳离子和中性分子。然而，CD表明该骨架接近中性，因此基于形式电荷计数得出的定性结论，例如关于客体包合性质的结论，将是不正确的。三种独特的苯二甲酸连接体的电荷分布存在显著差异，这些连接体在配位聚合物中广泛使用。这表明配位聚合物空腔的静电性质及其包合性质是高度可调的。电子密度拓扑表明，四面体配位的Co原子的原子体积比八面体配位的Co原子大15%。晶体结构同时具有铁磁和反铁磁相互作用，但CD中未发现直接的金属-金属键。因此，磁有序通过氧桥和芳族连接体中的超交换发生。对实验CD的键合分析表明，两个氧原子O(1)和O(11)对金属-配体键合有显著的共价贡献，而所有其他氧原子与金属有闭壳相互作用。这表明这两个氧原子是磁有序的关键介导者。
