Glaser Thorsten, Heidemeier Maik, Fröhlich Roland, Hildebrandt Peter, Bothe Eberhart, Bill Eckhard
Institut für Anorganische und Analytische Chemie, Westfälische Wilhelms-Universität Münster, Wilhelm-Klemm-Strasse 8, D-48149 Münster, Germany.
Inorg Chem. 2005 Jul 25;44(15):5467-82. doi: 10.1021/ic050268x.
The coordination chemistries of the triple tetradentate triplesalen ligands H(6)talen, H(6)talen(t)(-)(Bu)(2), and H(6)talen(NO)(2) have been investigated with nickel(II). These triplesalen ligands provide three salen-like coordination environments bridged in a meta-phenylene arrangement by a phloroglucinol backbone. The structures of the complexes [(talen)Ni(II)(3)], [(talen(t)(-)(Bu)(2)Ni(II)(3)], and [(talen(NO)(2)Ni(II)(3)] have been determined by single-crystal X-ray diffraction. All three compounds are composed of neutral trinuclear complexes with square-planar coordinated Ni(II) ions in a salen-like coordination environment. Whereas the overall molecular structure of [(talen(NO)(2)Ni(II)(3)] is nearly planar, the structures of [(talen)Ni(II)(3)] and [(talen(t)(-)(Bu)(2)Ni(II)(3)] are bowl-shaped as a result of ligand folding. The strongest ligand folding occurs at the central nickel-phenolate bond of [(talen(t)(-)(Bu)(2)Ni(II)(3)], resulting in the formation of a chiral hemispherical pocket. The dependence of the physical properties by the substituents on the terminal phenolates has been studied by FTIR, resonance Raman, UV-vis-NIR absorption, and electrochemistry. The three nickel-salen subunits are electronically interacting via the pi system of the bridging phloroglucinol backbone. The strength of this interaction is mediated by two opposing effects: the electron density at the terminal phenolates and the folding of the ligand at the central phenolates. The parent complex [(talen)Ni(II)(3)] is irreversibly oxidized at 0.32 V versus ferrocenium/ferrocene (Fc(+)/Fc), whereas [(talen(t)(-)(Bu)2)Ni(II)(3)] and [(talen(NO)(2)Ni(II)(3)] exhibit reversible oxidations at 0.22 V versus Fc(+)/Fc and 0.52 V versus Fc(+)/Fc, respectively. The oxidized species (talen(t)(-)(Bu)(2)Ni(3) and (talen(NO)(2)Ni(3) undergo a valence-tautomeric transformation involving a Ni(III) and a phenoxyl radical species, as observed by EPR spectroscopy. Thus, these oxidized forms exhibit the phenomena of valence tautomerism and mixed valence simultaneously. The extent of delocalization of the radical species and of the Ni(III) species is discussed.
已研究了三联四齿三水杨醛配体H(6)talen、H(6)talen(t)(-)(Bu)(2)和H(6)talen(NO)(2)与镍(II)的配位化学。这些三水杨醛配体提供了三个类似水杨醛的配位环境，它们通过间苯二酚骨架以间亚苯基排列方式桥连。配合物[(talen)Ni(II)(3)]、[(talen(t)(-)(Bu)(2)Ni(II)(3)]和[(talen(NO)(2)Ni(II)(3)]的结构已通过单晶X射线衍射确定。所有这三种化合物均由中性三核配合物组成，其中镍(II)离子在类似水杨醛的配位环境中呈平面正方形配位。[(talen(NO)(2)Ni(II)(3)]的整体分子结构近乎平面，而[(talen)Ni(II)(3)]和[(talen(t)(-)(Bu)(2)Ni(II)(3)]的结构由于配体折叠呈碗状。最强的配体折叠发生在[(talen(t)(-)(Bu)(2)Ni(II)(3)]的中心镍 - 酚盐键处，导致形成一个手性半球形口袋。通过傅里叶变换红外光谱（FTIR）、共振拉曼光谱、紫外 - 可见 - 近红外吸收光谱和电化学研究了末端酚盐上取代基对物理性质的影响。三个镍 - 水杨醛亚基通过桥连间苯二酚骨架的π体系进行电子相互作用。这种相互作用的强度由两种相反的效应介导：末端酚盐处的电子密度和中心酚盐处配体的折叠。母体配合物[(talen)Ni(II)(3)]相对于二茂铁鎓/二茂铁（Fc(+)/Fc）在0.32 V处不可逆氧化，而[(talen(t)(-)(Bu)2)Ni(II)(3)]和[(talen(NO)(2)Ni(II)(3)]相对于Fc(+)/Fc分别在0.22 V和0.52 V处表现出可逆氧化。氧化态物种(talen(t)(-)(Bu)(2)Ni(3)和(talen(NO)(2)Ni(3)经历了涉及Ni(III)和苯氧基自由基物种的价互变异构转变，这通过电子顺磁共振光谱（EPR）观察到。因此，这些氧化形式同时表现出价互变异构和混合价现象。讨论了自由基物种和Ni(III)物种的离域程度。
