This survey of metal–metal (MM) bond distances in binuclear complexes of the first row 3d-block elements reviews experimental and computational research on a wide range of such systems. The metals surveyed are titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, and zinc, representing the only comprehensive presentation of such results to date. Factors impacting MM bond lengths that are discussed here include (a) the formal MM bond order, (b) size of the metal ion present in the bimetallic core (M₂)ⁿ⁺, (c) the metal oxidation state, (d) effects of ligand basicity, coordination mode and number, and (e) steric effects of bulky ligands. Correlations between experimental and computational findings are examined wherever possible, often yielding good agreement for MM bond lengths. The formal bond order provides a key basis for assessing experimental and computationally derived MM bond lengths. The effects of change in the metal upon MM bond length ranges in binuclear complexes suggest trends for single, double, triple, and quadruple MM bonds which are related to the available information on metal atomic radii. It emerges that while specific factors for a limited range of complexes are found to have their expected impact in many cases, the assessment of the net effect of these factors is challenging. The combination of experimental and computational results leads us to propose for the first time the ranges and “best” estimates for MM bond distances of all types (Ti–Ti through Zn–Zn, single through quintuple).

中文翻译：

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第一排过渡金属钛通过锌的双核金属配合物中金属-金属（MM）的键距和键序

这项对第一行3d块元素的双核配合物中的金属-金属（MM）键距的调查回顾了在许多此类系统上的实验和计算研究。所调查的金属为钛，钒，铬，锰，铁，钴，镍，铜和锌，是迄今为止此类结果的唯一综合表述。这里讨论的影响MM键长的因素包括（a）正式的MM键序，（b）双金属核（M ₂）中存在的金属离子的大小^{n +}，（c）金属的氧化态，（d）配体碱度，配位方式和数量的影响，以及（e）庞大配体的空间位阻。尽可能检查实验结果与计算结果之间的相关性，通常对于MM键长产生良好的一致性。正式的粘结顺序为评估实验和计算得出的MM粘结长度提供了关键依据。金属变化对双核络合物中MM键长度范围的影响表明了单键，双键，三键和四倍MM键的趋势，这与金属原子半径的可用信息有关。结果表明，尽管发现在许多情况下，有限范围的配合物的特定因素均具有预期的影响，但评估这些因素的净效应却具有挑战性。