Hydrogen storage in dinuclear Pt(II) metallacycles Justine Kombarakkaran a , Juan C. Noveron b , Michael Helgesen b , Kai Shen a,1 , Tanja Pietraß a, * a Department of Chemistry, New Mexico Tech, Socorro, NM 87801, USA b Department of Chemistry, University of Texas at El Paso, 500W. University Ave., El Paso, TX 79968-0513, USA article info Article history: Received 29 July 2008 Received in revised form 2 February 2009 Accepted 6 May 2009 Available online 16 June 2009 Keywords: Hydrogen storage Platinum metallacycles NMR abstract Hydrogen gas physisorption in two distinct dinuclear Pt(II) metallacycles was investigated with 2 H nuclear magnetic resonance (NMR) spectroscopy. Hydrogen adsorption isotherm data and 2 H NMR spectroscopy indicated that hydrogen storage occurs via condensation within the cavities of one of the macrocycles and at the interstitial sites in the other. In addition, this study further supports the notion that heat of adsorption and pore size play critical roles in hydrogen storage. ª 2009 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved. 1. Introduction The development for an effective hydrogen storage medium that is safe, efficient, and light-weight has been a major impediment to the advent of a hydrogen-based industry and economy. The DOE 2010 target for a storage medium is 6 wt% at a density of 45 g/L [1], and to our knowledge no material has been shown to exhibit these criteria at STP. Carbon nanotubes (CNT) and metal organic framework (MOF) compounds have been considered good candidates for hydrogen storage due to their high surface areas and large pore volumes; however, it has been shown that surface area and pore volume do not necessarily correlate with uptake capacity [2], primarily because the heat of adsorption is generally too low to give rise to significant storage at ambient temperature [3]. Current experimental and theoretical work has focused on under- standing the fundamental molecular features that are responsible for hydrogen physisorption in the solid-state. Because MOF compounds offer many molecular design opportunities and their structure may be well-characterized, they are good platforms for studying hydrogen physisorption as a function of the nature of the molecular components. For example, one can analyze hydrogen storage as a function of the identity and oxidation state of the metal ions and the nature of the organic linkers in structurally characterized MOFs. Metal ions have been observed to give rise to higher binding energies with hydrogen. Sun et al. predicted that early representatives of the transition metal series such as Sc, Ti, and V give rise to such higher binding energies [1]. Similarly, Pt(0) nanoparticles have been shown to increase hydrogen absorption via the spillover effect in MOFs and CNTs [4], and the metal sites presumably increased the heat of adsorption of the gas [5]. Furthermore, Liu et al. demonstrated a strong * Corresponding author. Tel.: þ1 575 835 5586; fax: þ1 575 835 5364. E-mail address: tanja@nmt.edu (T. Pietraß). 1 Present address: Biochemistry Department, Wake Forest University School of Medicine, Medical Center Boulevard, Winston-Salem, NC 27157, USA. Available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/he 0360-3199/$ – see front matter ª 2009 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijhydene.2009.05.018 international journal of hydrogen energy 34 (2009) 5704–5709