The lowest-energy structure of thiolate-group-protected Au38(SR)24 is with ab initio computations. A unique bi-isocahedral Au23 core is predicted for the Au38(SR)24 cluster, consistent with recent experimental and theoretical confirmation of the icosahedral Au13 core for the [Au25(SR)18]- cluster. The computed optical absorption spectrum and X-ray diffraction pattern are in good agreement with experimental measurements. Like the "magic-number" cluster [Au25(SR)18]-, the high stability and selectivity of the magic-number Au38(SR)24 cluster is attributed to high structural compatibility between the bi-isocahedral Au23 core and the 18 exterior staple motifs.

The precise atomic structure of the recently synthesized "magic cluster" Au(20)(SR)(16) is predicted using ab initio calculations and global-minimum searches. The cluster contains a prolate Au(8) core and four level-3 extended staple motifs (-RS-Au-RS-Au-RS-Au-RS-). The simulated optical absorption spectra of the lowest-energy structures are in good agreement with the measured spectrum. The Au(20)(SR)(16) cluster, with a low Au/SR ratio of 1.25:1, may represent a structural evolution from core-free homoleptic clusters [Au(SR)](N) to core-stacked clusters.

A grand unified model (GUM) is developed to achieve fundamental understanding of rich structures of all 71 liganded gold clusters reported to date. Inspired by the quark model by which composite particles (for example, protons and neutrons) are formed by combining three quarks (or flavours), here gold atoms are assigned three ‘flavours' (namely, bottom, middle and top) to represent three possible valence states. The ‘composite particles' in GUM are categorized into two groups: variants of triangular elementary block Au3(2e) and tetrahedral elementary block Au4(2e), all satisfying the duet rule (2e) of the valence shell, akin to the octet rule in general chemistry. The elementary blocks, when packed together, form the cores of liganded gold clusters. With the GUM, structures of 71 liganded gold clusters and their growth mechanism can be deciphered altogether. Although GUM is a predictive heuristic and may not be necessarily reflective of the actual electronic structure, several highly stable liganded gold clusters are predicted, thereby offering GUM-guided synthesis of liganded gold clusters by design.

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