LZnX complexes of tripodal ligands with intramolecular RN–H hydrogen bonding groups: structural implications of a hydrogen bonding cavity, and of X/R in the hydrogen bonding geometry/strength
作者:Juan C. Mareque Rivas、Ravi Prabaharan、Rafael Torres Martín de Rosales、Laurent Metteau、Simon Parsons
DOI:10.1039/b407790c
日期:——
Tripodal ligands N(CH2Py)3ân(CH2Py-6-NHR)n
(R = H, n
= 1â3 L1â31â31â3, n
= 0 tpa; R = CH2tBu, n
= 1â3 Lâ²1â3â²1â3â²1â3) are used to investigate the effect of different hydrogen bonding microenvironments on structural features of their LZnX complexes (X = Clâ, NO3â, OHâ). The X-ray structures of [(L222)Zn(Cl)](BPh4)
2·0.5(H2O·CH3CN), [(L333)Zn(Cl)](BPh4)
3·CH3CN, [(Lâ²111)Zn(Cl)](BPh4)
1â², [(Lâ²222)Zn(Cl)](BPh4)
2â²Â·CH3OH, and [(Lâ²333)Zn(Cl)](BPh4)
3â² have been determined and exhibit trigonal bipyramidal geometries with intramolecular (internal) NâHâ¯ClâZn hydrogen bonds. The structure of [(Lâ²222)Zn(ONO2)]NO34â²Â·H2O with two internal NâHâ¯OâZn hydrogen bonds has also been determined. The axial ZnâCl distance lengthens from 2.275 Ã
in [(tpa)Zn(Cl)](BPh4) to 2.280â2.347 Ã
in 1â3, 1â²â3â². Notably, the average ZnâNpy distance is also progressively lengthened from 2.069 Ã
in [(tpa)Zn(Cl)](BPh4) to 2.159 and 2.182 Ã
in the triply hydrogen bonding cavity of 3 and 3â², respectively. Lengthening of the ZnâCl and ZnâNpy bonds is accompanied by a progressive shortening of the trans ZnâN bond from 2.271 Ã
in [(tpa)Zn(Cl)](BPh4) to 2.115 Ã
in 3
(2.113 Ã
in 3â²). As a result of the triply hydrogen bonding microenvironment the ZnâCl and ZnâNpy distances of 3 are at the upper end of the range observed for axial ZnâCl bonds, whereas the axial ZnâN distance is one of shortest among N4 ligands that induce a trigonal bipyramidal geometry. Despite the rigidity of these tripodal ligands, the geometry of the intramolecular RNâHâ¯XâZn hydrogen bonds (X = Clâ, OHâ, NO3â) is strongly dependent on the nature of X, however, on average, similar for R = H, CH2tBu.
利用三足配体 N(CH2Py)3ân(CH2Py-6-NHR)n(R = H,n = 1â3 L1â31â31â3,n = 0 tpa;R = CH2tBu,n = 1â3 Lâ²1â3â²1â3â²1â3)研究了不同氢键微环境对其 LZnX 复合物(X = Clâ、NO3â、OHâ)结构特征的影响。(L222)Zn(Cl)](BPh4) 2Â-0.5(H2OÂ-CH3CN)、[(L333)Zn(Cl)](BPh4) 3Â-CH3CN、[(Lâ²111)Zn(Cl)](BPh4) 1â²、[(Lâ²222)Zn(Cl)](BPh4) 2â²Â-CH3OH、和[(Lâ²333)Zn(Cl)](BPh4) 3â²的结构已经确定,它们呈现出具有分子内(内部)NâHâ¯ClâZn氢键的三叉双锥体几何结构。此外,还确定了具有两个内部 NâHâ¯OâZn 氢键的 [(Lâ²222)Zn(ONO2)]NO34â²Â-H2O 结构。ZnâCl的轴向距离从[(tpa)Zn(Cl)](BPh4)中的2.275 Ã延长到1â3, 1â²â3â²中的2.280â2.347 Ã。值得注意的是,ZnâNpy的平均距离也从[(tpa)Zn(Cl)](BPh4)中的2.069 Ã逐渐延长到3和3â²的三氢键空腔中的2.159 Ã和2.182 Ã。随着 ZnâCl 和 ZnâNpy 键的延长,反式 ZnâN 键也逐渐缩短,从[(tpa)Zn(Cl)](BPh4) 中的 2.271 à 到 3 中的 2.115 Ã(3â² 中为 2.113 Ã)。由于存在三重氢键微环境,3 的 ZnâCl 和 ZnâNpy 间距处于轴向 ZnâCl 键所观察到的范围的上限,而轴向 ZnâN 间距则是诱导出三叉双锥几何结构的 N4 配体中最短的距离之一。尽管这些三足配体具有刚性,但分子内 RNâHâ¯XâZn 氢键(X = Clâ、OHâ、NO3â)的几何形状在很大程度上取决于 X 的性质,但平均而言,R = H、CH2tBu 时的几何形状相似。