Mason Kevin, Rogers Nicola J, Suturina Elizaveta A, Kuprov Ilya, Aguilar Juan A, Batsanov Andrei S, Yufit Dmitry S, Parker David
Department of Chemistry, Durham University , South Road, Durham DH1 3LE, U.K.
School of Chemistry, University of Southampton , Highfield, Southampton SO17 1BJ, U.K.
Inorg Chem. 2017 Apr 3;56(7):4028-4038. doi: 10.1021/acs.inorgchem.6b02291. Epub 2017 Mar 15.
Ytterbium and yttrium complexes of octadentate ligands based on 1,4,7,10-tetraazacyclododecane with a coordinated pyridyl group and either tricarboxylate (L) or triphosphinate (L) donors form twisted-square-antiprismatic structures. The former crystallizes in the centrosymmetric group P2/c, with the two molecules related by an inversion center, whereas the latter was found as an unusual kryptoracemate in the chiral space group P2. Pure shift NMR and EXSY spectroscopy allowed the dynamic exchange between the (RRR)-Δ-(δδδδ) and (RRR)-Λ-(λλλλ) TSAP diastereomers of the [Y.L] complex to be detected. The rate-limiting step in the exchange between Δ and Λ isomers involves cooperative ligand arm rotation, which is much faster for [Ln.L] than for [Ln.L]. Detailed analysis of NOESY, COSY, HSQC, and HMBC spectra confirms that the major conformer in solution is (RRR)-Λ-(λλλλ), consistent with crystal structure analysis and DFT calculations. The magnetic susceptibility tensors for [Yb.L] and [Yb.L], obtained from a full pseudocontact chemical shift analysis, are very different, in agreement with a CASSCF calculation. The remarkably different pseudocontact shift behavior is explained by the change in the orientation of the pseudocontact shift field, as defined by the Euler angles of the susceptibility tensor.
基于1,4,7,10-四氮杂环十二烷且带有一个配位吡啶基以及三羧酸酯（L）或次膦酸酯（L）供体的八齿配体的镱和钇配合物形成扭方反棱柱结构。前者在中心对称空间群P2/c中结晶，两个分子通过一个反演中心相关联，而后者在手性空间群P2中以一种不寻常的隐外消旋体形式被发现。纯位移核磁共振和EXSY光谱使得能够检测到[Y.L]配合物的（RRR）-Δ-（δδδδ）和（RRR）-Λ-（λλλλ）扭方反棱柱非对映异构体之间的动态交换。Δ和Λ异构体之间交换的限速步骤涉及协同配体臂旋转，对于[Ln.L]而言这比[Ln.L]要快得多。对NOESY、COSY、HSQC和HMBC光谱的详细分析证实，溶液中的主要构象体是（RRR）-Λ-（λλλλ），这与晶体结构分析和密度泛函理论计算结果一致。通过全赝接触化学位移分析获得的[Yb.L]和[Yb.L]的磁化率张量非常不同，这与CASSCF计算结果相符。显著不同的赝接触位移行为可通过由磁化率张量的欧拉角定义的赝接触位移场方向的变化来解释。
