Cluster Core Isomerism Induced by Crystal Packing Effects in the [HCo(15)Pd(9)C(3)(CO)(38)](2–) Molecular Nanocluster

[Image: see text] This article describes a rare case of cluster core isomerism in a large molecular organometallic nanocluster. In particular, two isomers of the [HCo(15)Pd(9)C(3)(CO)(38)](2–) nanocluster, referred as TP-Pd(9) and Oh-Pd(9), have been structurally characterized by single-crystal X-ray crystallography as their [NMe(3)(CH(2)Ph)](2)[HCo(15)Pd(9)C(3)(CO)(38)]·CH(2)Cl(2) (ca. 1:1 TP-Pd(9) and Oh-Pd(9) mixture), [NMe(3)(CH(2)Ph)](2)[HCo(15)Pd(9)C(3)(CO)(38)]·2CH(2)Cl(2) (mainly TP-Pd(9)), [NEt(3)(CH(2)Ph)](2)[HCo(15)Pd(9)C(3)(CO)(38)]·CH(2)Cl(2) (mainly TP-Pd(9)), [MePPh(3)](2)[HCo(15)Pd(9)C(3)(CO)(38)]·2.5CH(2)Cl(2) (mainly TP-Pd(9)), and [MePPh(3)](2)[HCo(15)Pd(9)C(3)(CO)(38)] (Oh-Pd(9)) salts. The cluster core of TP-Pd(9) is a tricapped trigonal prism, whereas this is a tricapped octahedron in Oh-Pd(9). The presence in the solid state of the Oh-Pd(9) or TP-Pd(9) isomers depends on the cation employed and/or the number and type of co-crystallized solvent molecules. Often, mixtures of the two isomers, within the same single crystal or as mixtures of different crystals within the same crystallization batch, are obtained. Structural isomerism in organometallic nanoclusters is discussed and compared to that in Au–thiolate nanoclusters.