Lieberman Craig M, Barry Matthew C, Wei Zheng, Rogachev Andrey Yu, Wang Xiaoping, Liu Jun-Liang, Clérac Rodolphe, Chen Yu-Sheng, Filatov Alexander S, Dikarev Evgeny V
Department of Chemistry, University at Albany , Albany, New York 12222, United States.
Department of Chemistry, Illinois Institute of Technology , Chicago, Illinois 60616, United States.
Inorg Chem. 2017 Aug 21;56(16):9574-9584. doi: 10.1021/acs.inorgchem.7b01032. Epub 2017 Jul 31.
A series of mixed-valent, heterometallic (mixed-transition metal) diketonates that can be utilized as prospective volatile single-source precursors for the low-temperature preparation of MM'O spinel oxide materials is reported. Three iron-cobalt complexes with Fe/Co ratios of 1:1, 1:2, and 2:1 were synthesized by several methods using both solid-state and solution reactions. On the basis of nearly quantitative reaction yields, elemental analyses, and comparison of metal-oxygen bonds with those in homometallic analogues, heterometallic compounds were formulated as [Fe(acac)][Co(hfac)] (1), [Co(hfac)][Fe(acac)][Co(hfac)] (2), and [Fe(hfac)][Fe(acac)][Co(hfac)] (3). In the above heteroleptic complexes, the Lewis acidic, coordinatively unsaturated Co/Fe centers chelated by two hexafluoroacetylacetonate (hfac) ligands maintain bridging interactions with oxygen atoms of acetylacetonate (acac) groups that chelate the neighboring Fe metal ion. Preliminary assignment of Fe and Co positions/oxidation states in 1-3 drawn from X-ray structural investigation was corroborated by a number of complementary techniques. Single-crystal resonant synchrotron diffraction and neutron diffraction experiments unambiguously confirmed the location of Fe and Co sites in the molecules of dinuclear (1) and trinuclear (2) complexes, respectively. Direct analysis in real time mass spectrometry revealed the presence of Fe- and Co-based fragments in the gas phase upon evaporation of precursors 1 and 2 as well as of Fe, Fe, and Co species for complex 3. Theoretical investigation of two possible "valent isomers", [Fe(acac)][Co(hfac)] (1) and [Co(acac)][Fe(hfac)] (1'), provided an additional support for the metal site/oxidation state assignment giving a preference of 6.48 kcal/mol for the experimentally observed molecule 1. Magnetic susceptibility measurements data are in agreement with the presence of high-spin Fe and Co magnetic centers with weak anti-ferromagnetic coupling between those in molecules of 1 and 2. Highly volatile heterometallic complexes 1-3 were found to act as effective single-source precursors for the low-temperature preparation of iron-cobalt spinel oxides FeCoO known as important materials for diverse energy-related applications.
报道了一系列混合价态的异金属（混合过渡金属）二酮化合物，它们可用作在低温下制备MM'O尖晶石氧化物材料的潜在挥发性单源前驱体。通过固态和溶液反应等多种方法合成了三种铁钴比为1:1、1:2和2:1的铁钴配合物。基于近乎定量的反应产率、元素分析以及与同金属类似物中金属-氧键的比较，将异金属化合物分别配制成[Fe(acac)][Co(hfac)]（1）、[Co(hfac)][Fe(acac)][Co(hfac)]（2）和[Fe(hfac)][Fe(acac)][Co(hfac)]（3）。在上述异配体配合物中，由两个六氟乙酰丙酮（hfac）配体螯合的路易斯酸性、配位不饱和的Co/Fe中心与螯合相邻Fe金属离子的乙酰丙酮（acac）基团的氧原子保持桥连相互作用。通过多种互补技术证实了从X射线结构研究得出的1-3中Fe和Co的位置/氧化态的初步归属。单晶共振同步加速器衍射和中子衍射实验分别明确证实了双核（1）和三核（2）配合物分子中Fe和Co位点的位置。实时直接分析质谱显示，前驱体1和2蒸发后气相中存在基于Fe和Co的碎片，配合物3则存在Fe、Fe和Co物种。对两种可能的“价异构体”[Fe(acac)][Co(hfac)]（1）和[Co(acac)][Fe(hfac)]（1'）的理论研究为金属位点/氧化态的归属提供了额外支持，实验观察到的分子1比其更具6.48 kcal/mol的优势。磁化率测量数据与高自旋Fe和Co磁性中心的存在一致，且1和2分子中的这些中心之间存在弱反铁磁耦合。发现高挥发性的异金属配合物1-3可作为低温制备铁钴尖晶石氧化物FeCoO的有效单源前驱体，FeCoO是用于多种能源相关应用的重要材料。
