Creutz Sidney E, Peters Jonas C
Division of Chemistry and Chemical Engineering, California Institute of Technology , Pasadena, California 91125, United States.
Inorg Chem. 2016 Apr 18;55(8):3894-906. doi: 10.1021/acs.inorgchem.6b00066. Epub 2016 Apr 4.
Low-coordinate transition-metal complexes that undergo spin crossover remain rare. We report here a series of four-coordinate, pseudo-tetrahedral P3FeII–X complexes supported by tris(phosphine)borate P3 ([PhBP3R]−) and phosphiniminato X-type ligands (−N═PR3′) that, in combination, tune the spin-crossover behavior of the system. Most of the reported iron complexes undergo spin crossover at temperatures near or above room temperature in solution and in the solid state. The change in spin state coincides with a significant change in the degree of π-bonding between Fe and the bound N atom of the phosphiniminato ligand. Spin crossover is accompanied by striking changes in the ultraviolet–visible (UV-vis) absorption spectra, which allows for quantitative modeling of the thermodynamic parameters of the spin equilibria. These spin equilibria have also been studied by numerous techniques including paramagnetic nuclear magnetic resonance (NMR), infrared, and Mössbauer spectroscopies; X-ray crystallography; and solid-state superconducting quantum interference device (SQUID) magnetometry. These studies allow qualitative correlations to be made between the steric and electronic properties of the ligand substituents and the enthalpy and entropy changes associated with the spin equilibria.
发生自旋交叉的低配位过渡金属配合物仍然很少见。我们在此报告了一系列由三（膦）硼酸酯P3（[PhBP3R]−）和磷亚胺基X型配体（−N═PR3′）支撑的四配位、假四面体P3FeII–X配合物，它们共同调节了体系的自旋交叉行为。大多数已报道的铁配合物在溶液和固态中于接近或高于室温的温度下发生自旋交叉。自旋态的变化与Fe和磷亚胺基配体中键合的N原子之间π键合程度的显著变化相一致。自旋交叉伴随着紫外可见（UV-vis）吸收光谱的显著变化，这使得能够对自旋平衡的热力学参数进行定量建模。这些自旋平衡也通过多种技术进行了研究，包括顺磁共振核磁共振（NMR）、红外和穆斯堡尔光谱；X射线晶体学；以及固态超导量子干涉装置（SQUID）磁力测定法。这些研究使得能够在配体取代基的空间和电子性质与自旋平衡相关的焓变和熵变之间建立定性关联。
