High-valent Cu, Ag, and Au coordination compounds

Coinage metals (Cu, Ag, Au) are late transition metals that belong to Group 11 of the periodic table. Their electronic configuration (Cu 3d¹⁰4s¹, Ag 4d¹⁰5s¹, Au 5d¹⁰6s¹) confers them a very rich chemistry in the oxidation state þ1, forming complexes with a d¹⁰ configuration with no d-d electronic transitions and coordination numbers from 2 to 4.¹ Geometries range from tetrahedral to trigonal planar or linear, depending on the metal. In addition, the lanthanide contraction confers to gold the so-called “relativistic effect”,² which is translated to gold radius contraction and the typical linear coordination for Au(I). On the other hand, coinage metals with oxidation state þ2 are very common for copper (3d⁹ configuration exhibiting a Jahn-Teller effect), very rare and highly oxidizing for silver,³ and also rare for gold, unless Au(II)eAu(II) metallic bonds are featured in dinuclear species.⁴ Coinage metal complexes exhibiting the higher oxidation state M(III), sharing a d⁸ electronic configuration that induces square-planar geometry stabilization, are rare for copper, relatively common for silver and very common for gold. The latter is due to the relativistic effects that cause an expansion of 5d orbitals and confers high stability to Au(III) complexes. On the contrary, M(IV) oxidation states are extremely rare and only scarce Cu(IV) inorganic compounds are known, i.e. Cs₂CuF₆.⁵ In this chapter, we will focus on higher oxidation state M(III) coinage metal complexes, describing the types of coordination environments capable of stabilizing this high oxidation state for each metal. Bioinspired non-organometallic and organometallic M(III) compounds will be extensively described....