SSCr Meeting, Bern, 2006 J-N. Chotard, Y. Filinchuk, K. Yvon

La2MgNi2H8, the first mixed polyanionic

transition metal hydride

J-N. Chotard, Y. Filinchuk, K. Yvon

Introduction

Complex metal hydrides

~ 80 compounds containing ~ 30 different

transition metal hydride complexes:

almost all of them are mononuclear

1st polynuclear hydride complexes based on 3d-metal

[Ni2H7]7- & [Ni4H12]12-

SSCr Meeting, Bern, 2006 J-N. Chotard, Y. Filinchuk, K. Yvon

Synthesis and structure determ.

• La2MgNi2: arc-melting La and Ni, sintering the product with Mg

• La2MgNi2H8: hydrogenation/deuteration in an autoclave:30 bar, 100°C

High-resolution synchrotron powder diffraction (SNBL at ESRF):indexing, metal structure (FOX), Rietveld

High-resolution neutron powder diffraction (HRPT, SINQ, PSI):16 deuterium atom positions (FOX), Rietveld

SSCr Meeting, Bern, 2006 J-N. Chotard, Y. Filinchuk, K. Yvon

Structure of La2MgNi2H8

Metal atom shifts < 0.65 Å

11.84 7.8211.96 Å92.78 °

7.643.94 Å

Tetragonal Monoclinic

SSCr Meeting, Bern, 2006 J-N. Chotard, Y. Filinchuk, K. Yvon

La2MgNi2 La2MgNi2H8

Two types of D-atom positionsLa2MgNi2

La2MgNi2H8

SSCr Meeting, Bern, 2006 J-N. Chotard, Y. Filinchuk, K. Yvon

Bonding :18 electron rule

34 electrons 64 electrons

La3+, Mg2+ [Ni2H7]7-, [Ni4H12]12-, H-

This concept is supported by observed changes in physical properties

SSCr Meeting, Bern, 2006 J-N. Chotard, Y. Filinchuk, K. Yvon