Fig. 2. Synthesis and characterisation of C-centred pentagold(I) clusters.

a Etching syntheses of CAu^I₆ clusters^26,43 to CAu^I₅ clusters using cis-1,2-bis(diphenylphosphino)ethene (cis-depe) (Suppl. Fig. 1). b Single-crystal X-ray diffraction (SCXRD) structures of the cations [(C)(Au^I-L)₅]⁺ (L = SS- and RR-NHC) and the CAu^I₅ cores of SS- and RR-2^NHC with optically active NHC ligands. c SCXRD structures of the cation [(C)(Au^I-TPP)₅]^+ 46 and the core of 2^TPP with TPP. d Microscopy images of crystals of SS-2^NHC (orange crystals) and 2^TPP (yellow crystals) under ambient light. e Explanation and examples of geometry index τ values⁵¹, which is used for showing the geometric differences of CAu^I₅ cores with NHCs and TPP (Table 1). The τ value represents the geometric difference between the regular square pyramidal (τ = 0) and trigonal bipyramidal (τ = 1), τ = (β – α)/60°, where α and β are the two largest basal angles. Colour code: Au, yellow; C, grey; N, blue; P, orange; H, white. BF₄^– counterions and solvent molecules are omitted for clarity.