CLUSTER OF CLUSTERS - A MODULAR APPROACH TO LARGE METAL-CLUSTERS - STRUCTURAL CHARACTERIZATION OF A 38-ATOM CLUSTER [(PARA-TOL3P)12AU18AG20CL14] BASED ON VERTEX-SHARING TRIICOSAHEDRA

The crystal and molecular structure of a 38-atom metal cluster, (p-Tol3P)12Au18Ag20Cl14 (I), has been determined by single-crystal X-ray crystallography. The cluster (p-Tol3P)12Au18Ag20Cl14·42EtOH crystallizes in a triclinic unit cell of P-1 space group with lattice parameters a = 23.094 (11) Å, b = 31.950 (17), c = 34.178 (17) Å, α = 112.76 (4)°, β = 90.04 (3)γ, = 97.92 (3)°, and Z = 2. The structure was refined to R1 = 10.1%, R2 = 11.8% for 8150 independent reflections with I > 3σ(I). The metal framework of 1 can be described as three 13-atom centered icosahedra sharing three vertices in a triangular array plus two capping Ag atoms on the pseudo-3-foId axis. As such, it belongs to a novel series of high-nuclearity Au-Ag clusters whose structures are based on vertex-sharing (centered) icosahedra. Empirical structural rules for these Au-Ag supraclusters are developed. The structural systematics of this new class of supraclusters led to the concept of “cluster of clusters”, which is useful in the design, preparation, and characterization of large metal clusters of increasingly high nuclearity via vertex-, edge-, and face-sharing and/or close packing of smaller cluster units as building blocks (viz., a modular approach to large clusters). Simple electron counting of this and related clusters based on a cluster of clusters (C2) model is also discussed in order to rationalize the observed structural parameters and the electronic requirements. © 1990, American Chemical Society. All rights reserved.