Growth mechanism and chemical bonding in scandium-doped copper clusters: experimental and theoretical study in concert.

Size matters! The electronic structure and size-dependent stability of neutral and cationic scandium-doped copper clusters have been investigated by mass spectrometric studies (for the cations) and also quantum chemical computations. The proposed reaction paths ultimately lead to the most stable Frank-Kasper-shaped Cu(16)Sc(+) cluster (shown here), which could be the germ of a new crystallization process.Electronic structure and size-dependent stability of scandium-doped copper cluster cations, Cu(n)Sc(+), were investigated by using a dual-target dual-laser vaporization production scheme followed by mass spectrometric studies and also quantum chemical computations in the density functional theory framework. The neutral species also were studied by using computational methods. Enhanced abundances and dissociation energies were measured in the case of Cu(n)Sc(+) for n=4, 6, 8, 10 and 16, the last of these identified as being extraordinary stable. Neutral clusters are stable with n=5, 7, 9 and 15, which are isoelectronic with respect to the number of the valence s electrons with the stable cationic clusters; hence a simple electron count determines cluster properties to a great extent. The Cu(17)Sc cluster was found to be a superatomic molecule, containing Cu(16)Sc(+) and Cu(-) units; however, the charge separation is not as pronounced as in the case of CuLi. Cu(15)Sc was found to be a stable cluster with a large dissociation energy and a closed electronic structure; hence this can be regarded as a superatom, analogous to the noble gases. The main factors determining the growth patterns of these clusters are the central position of the scandium atom and the successive filling of the shell orbitals. For smaller clusters, the reaction paths appear to diverge yielding various products; however all paths ultimately lead to the most stable Frank-Kasper shaped Cu(16)Sc cluster, which in turn can be the germ of the crystallization process.