Molecular heterometallic hydride clusters composed of rare-earth and d -transition metals Takanori Shima 1 , Yi Luo 2 , Timothy Stewart 3 , Robert Bau 3 , Garry J. McIntyre 4† , Sax A. Mason 4 and Zhaomin Hou 1,2 * Heteromultimetallic hydride clusters containing both rare-earth and d-transition metals are of interest in terms of both their structure and reactivity. However, such heterometallic complexes have not yet been investigated to a great extent because of difficulties in their synthesis and structural characterization. Here, we report the synthesis, X-ray and neutron diffraction studies, and hydrogen addition and release properties of a family of rare-earth/d-transition-metal heteromultimetallic polyhydride complexes of the core structure type ‘Ln 4 MH n ’ (Ln 5 Y, Dy, Ho; M 5 Mo, W; n 5 9, 11, 13). Monitoring of hydrogen addition to a hydride cluster such as [{(C 5 Me 4 SiMe 3 )Y} 4 (m-H) 9 Mo(C 5 Me 5 )] in a single-crystal to single-crystal process by X-ray diffraction has been achieved for the first time. Density functional theory studies reveal that the hydrogen addition process is cooperatively assisted by the Y/Mo heteromultimetallic sites, thus offering unprecedented insight into the hydrogen addition and release process of a metal hydride cluster. M etal hydrides are fundamental components in a wide range of stoichiometric and catalytic reactions, and their impor- tance in modern chemistry cannot be overemphasized. Heterometallic hydride complexes consisting of both rare-earth and d-transition metals are of great interest, as they may exhibit unique reactivity possibly resulting from the multi-metallic synergy effect of the two substantially different types of metals 1–6 . Well-defined hydride clusters of this type are also of particular inter- est as molecular models for hydrogen storage alloys, in view of the fact that rare earth/d-transition metal alloys such as LaNi 5 H x are excellent hydrogen-storage materials 7–10 . However, well-defined rare-earth/d-transition metal polyhydride complexes that allow an extensive study of the chemistry of hydrogen in the heterometallic coordination environment remain scarce because of the lack of a strategy for efficient synthesis and difficulty in characterization of the hydride species. The first rare-earth/d-transition metal heteromultimetallic polyhydride complex without X-ray structure determination was reported by Evans and co-workers in 1984 as an adduct of the yttrium metallocene hydride [(C 5 H 4 Me) 2 YH(THF)] 2 (THF, tetra- hydrofuran) and 0.5 equiv. of [(C 5 H 4 Me) 2 ZrH 2 ] 2 (ref. 11). A few years later, the groups of Caulton and Evans reported the synthesis of the first structurally characterized rare-earth/d-transition metal polyhydride complex by a methane elimination reaction of the yttrium metallocene methyl complex [(C 5 H 5 ) 2 YMe(THF)] with the rhenium hydride ReH 7 (PPh 3 ) 2 (refs 12, 13). Recently, Kempe and co-workers used a similar alkane elimination strategy to synthesize an yttrium/ruthenium heterotrimetallic trihydride complex, but the hydride ligands in the resulting complex were not located by X-ray analysis 14 . We recently synthesized several structurally characterized heteromultimetallic polyhydride com- plexes of rare-earth and d-transition metals by an alkane elimination reaction of half-sandwich rare-earth dialkyl complexes with d-tran- sition metal hydrides 15,16 . Tilley and co-workers reported the synthesis of a samarium/tungsten heterobimetallic dihydride complex by H 2 elimination from metallocene hydrides [(C 5 Me 5 ) 2 SmH] 2 and [(C 5 H 5 ) 2 WH 2 ], but the hydride ligands were not located 17 . Green and co-workers reported the synthesis of heterometallic hydride complexes of ytterbium with tungsten and niobium by a salt metathesis reaction between YbI 2 and the potassium salts of the d-transition metals 18 . Except for one preliminary example 11 , all of the rare-earth/ d-transition metal heterometallic hydride complexes reported so far in the literature have been constructed by using mononuclear rare-earth species as building blocks. Heterometallic polyhydride complexes containing polynuclear rare-earth species with d-tran- sition metals have not been reported previously. The reaction chemistry of rare-earth/d-transition metal heteromultimetallic polyhydrides has remained almost unexplored to date. The groups of Takats 19–21 , Okuda 22,23 and Kempe 24,25 , as well as ours 6,26–40 , have recently reported that homometallic polynuclear rare-earth polyhydride complexes such as [{(C 5 Me 4 SiMe 3 )Ln(m- H) 2 } 4 (THF) n ] (Ln ¼ Sc, Y or a lanthanide metal; n ¼ 0–2) can exhibit unique structures and reactivities that are exquisitely different from their monohydride relatives. Here, we report the use of the tetranuclear rare-earth octahydride complexes [{Cp ′ Ln(m-H) 2 } 4 (THF)] (Cp ′ ¼ C 5 Me 4 SiMe 3 ; Ln ¼ Y, Dy, Ho) as building blocks for the synthesis of a novel series of well-defined Ln 4 MH n -type (Ln ¼ Y, Dy, Ho; M ¼ Mo, W; n ¼ 9, 11, 13) heteromultimetallic hydride clusters. Unprecedented structural features and unique hydrogen addition and release properties are revealed by 1 H NMR, X-ray and neutron diffraction and density functional theory (DFT) studies. Moreover, monitoring of hydrogen addition to a hydride cluster in a single-crystal to single-crystal process by X-ray diffraction has been achieved for the first time. These studies have offered unprecedented insight into the hydrogen addition and release process of a polyhydride complex. 1 Organometallic Chemistry Laboratory and Advanced Catalyst Research Team, RIKEN Advanced Science Institute, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan, 2 State Key Laboratory of Fine Chemicals and School of Chemical Engineering, Dalian University of Technology, 158 Zhongshan Road, Dalian 116012, China, 3 Department of Chemistry, University of Southern California, Los Angeles, California 90089, USA, 4 Institut Laue-Langevin, 6 rue Jules Horowitz, BP 156, 38042 Grenoble, Cedex 9, France; † Present address: The Bragg Institute, Australian Nuclear Science and Technology Organisation, Lucas Heights, Kirrawee, New South Wales 2232, Australia. *e-mail: houz@riken.jp ARTICLES PUBLISHED ONLINE: 18 SEPTEMBER 2011 | DOI: 10.1038/NCHEM.1147 NATURE CHEMISTRY | VOL 3 | OCTOBER 2011 | www.nature.com/naturechemistry 814 © 2011 Macmillan Publishers Limited. All rights reserved.