Relation between Crystal Packing and Optical Anisotropy for Schiff Base-Nickel Complexes that Form Various Ladder-like Hydrogen-Bonding Networks

A series of nickel(II) complexes of a 2,6-dihydroxynaphtho-1-aldehyde Schiff base was synthesized. By means of in situ formation of metal-containing tectons, some of those complexes afforded sub-millimeter-scale single crystals directly from the reaction mixture. The complexes consisted in part of various ladder-like hydrogen-bonded networks, which forced the chromophore to arrange in anisotropic fashion, with the effect dependent on the length of the alkyl chains. The crystals exhibited a marked linear dichroism, and their solid-state polarization absorption spectra were recorded with an optical microscope. Using data from quantum chemical calculations and the crystal structure, we were able to elucidate the relationship between crystal packing and optical anisotropy. Analyses based on theoretical equations allowed us to explain the observed absorbance and to interpret the mechanism of the dichroism in detail.本研究合成了一系列基于2,6-二羟基萘-1-醛希夫碱（Schiff base）的二价镍配合物。通过原位生成含金属结构基元（metal-containing tectons）的策略，部分此类配合物可直接从反应混合物中获得亚毫米级单晶。此类配合物的部分结构由多种梯形氢键网络构成，该网络迫使生色团以各向异性方式排布，且排布效果依赖于烷基链的长度。所制备的晶体表现出显著的线性二色性（linear dichroism），研究人员借助光学显微镜记录了其固态偏振吸收光谱。结合量子化学计算数据与晶体结构信息，我们阐明了晶体堆积与光学各向异性之间的构效关系。基于理论公式开展的分析，不仅解释了实验观测到的吸光度变化，还详细阐释了该线性二色性的产生机制。