DOI: 10.1002/chem.200800376 Magnetic Endohedral Transition-Metal-Doped Semiconduncting- Nanoclusters Jon M. Matxain,* Elena Formoso, Jose M. Mercero, Mario Piris, Xabier Lopez, and Jesus M. Ugalde [a] Introduction The properties of nanoparticles and nanoclusters differ with respect to those of their corresponding bulk material. How- ever, as their bulk counterparts, nanoclusters can also be doped and, consequently, their properties be modified at will. [1] Among nanocluster structural motifs, interest in hollow spherical structures has increased since the discovery of carbon buckminsterfullerenes. [2] These carbon clusters are able to build up molecular solids, in which each unit keeps itsstructure,similartothatofourisolatedcluster. [3] The electronic properties of these fullerenes and the solids made of them, fullerites, may be altered by the intro- duction of dopants, thereby yielding new materials with tail- ored properties. Fullerenes have been doped in three differ- ent ways: i)By substituting one or several carbon atoms by othersimilaratoms,suchasB,N,orSitoyieldthesocalled heterofullerenes, first produced by Smalley)s group [4] in 1991; ii)Exohedrally, compounds in which atoms are placed outsidethefullerenecages.Ithasbeenfoundthatbyexohe- dral doping a number of fullerites can be altered from the non-doped insulator to semiconductors, [5] or even high-tem- perature superconductors; [6,7] iii)Endohedrally, whereby atoms or molecules are trapped inside the fullerenes. The earliest one, La@C 60 , was discovered by Heath et al. in 1985, [8] and after that many others have been found and their electronic structures explained. [9–13] Remarkably, no transition-metal atoms have been found encapsulated inside fullerenes. [14] Boronnitride(BN)clustersaretheonesnextmostwidely studied hollow nanoclusters, owing to the fact that the BN unit is isoelectronic to C 2 . A large amount of BN fullerenes, suchasB i N i , i = 12,15,24,28–60, have been investigated both theoreticallyandexperimentally. [15–26] Abstract: Endohedral first-row transi- tion-metal-doped TM@Zn i S i nanoclus- ters, in which TM stands for the first- row transition-metals from Sc to Zn, and i = 12, 16, have been characterized. In these structures the dopant metals are trapped inside spheroidal hollow semiconducting nanoclusters. It is ob- served that some of the transition metals are trapped in the center of mass of the cluster, whereas others are found to be displaced from that center, leading to structures in which the tran- sition metals display a complex dynam- ical behavior upon encapsulation. This fact was confirmed by quantum molec- ular dynamics calculations, which fur- ther confirmed the thermal stability of endohedral compounds. In the endohe- drally-doped nanoclusters in which the transition-metal atom sits on the center of mass, the host hollow cluster struc- ture remains undistorted after dopant encapsulation.Conversely,iftheencap- sulated transition-metal atom is dis- placed from the center of mass, the host hollow cluster structure suffers a very tiny distortion. Additionally, it is found that there is negligible charge transfer between the dopant transition- metal atom and its hollow cluster host and, after encapsulation, the spin den- sities remain localized on the transi- tion-metal atom. This allows for the atomic-like behavior of the trapped transition-metal atom, which gives rise to their atomic-like magnetic proper- ties. The encapsulation free energies are negative, suggesting that these compounds are thermodynamically stable. Keywords: ab initio calculations · endohedral compounds · inorganic fullerenes · semiconducting nano- clusters · transitionmetals [a] Dr.J.M.Matxain,Dr.E.Formoso,Dr.J.M.Mercero,Dr.M.Piris, Dr.X.Lopez,Prof.Dr.J.M.Ugalde Kimika Fakultatea, Euskal Herriko Unibertsitatea and Donostia International Physics Center (DIPC) P.K.1072,20080Donostia,Euskadi(Spain) Fax:(+ 34)943015270 E-mail:jonmattin.matxain@ehu.es Chem. Eur. J. 2008, 14,8547–8554 #2008Wiley-VCHVerlagGmbH&Co.KGaA,Weinheim 8547 FULL PAPER