A Thermally Stable Pt/Y-Based Metal-Organic Framework: Exploring the Accessibility of the Metal Centers with Spectroscopic Methods Using H 2 O, CH 3 OH, and CH 3 CN as Probes Kai Chung Szeto, ²,‡ Karl Petter Lillerud, ²,‡ Mats Tilset, ² Morten Bjørgen, ²,‡,# Carmelo Prestipino, §,⊥ Adriano Zecchina, § Carlo Lamberti, § and Silvia Bordiga* ,§ Department of Chemistry, UniVersity of Oslo, P.O. Box 1033, N-0315, Oslo, Norway, Centre of Materials Science and Nanotechnology, P.O. Box 1162, N-0318, Oslo, Norway, and Department of Inorganic, Physical and Materials Chemistry, NIS Centre of Excellence, and Centro di Riferimento INSTM, UniVersity of Turin, Via P. Giuria 7, I-10125, Torino, Italy ReceiVed: June 4, 2006; In Final Form: August 7, 2006 A metal-organic framework (MOF) based on Pt, Y, and 2,2′-bipyridine-5,5′-dicarboxylate (BPDC), stable up to 400 °C, has been synthesized and characterized. In this MOF, the Pt centers are coordinated to Cl and the N atoms of the BPDC unit, giving a local environment similar to that found in a series of Pt-organic complexes with catalytic activity toward C-H bond cleavage of alkanes. This new material is a heterogeneous counterpart to the corresponding metal-organic complex. The structure, determined by single-crystal XRD data, is the repetition of three covalently bonded layers. These layers form a block, which is stacking as an (a)(b)(c) sequence along the crystallographic b-axis. Each layer contains the Pt-organic unit, while Y atoms represent the connection between adjacent layers. No covalent connection is present between layer (a) of a block and layer (c) of an adjacent block. EXAFS (BM29 at the ESRF) analysis supports the XRD data. As this MOF crystallizes under hydrothermal conditions, water acts both as solvent and as a direct ligand of Y. Accessibility to the metal centers is demonstrated by reversible water desorption/readsorption, as determined by TPA/TPD, FTIR, UV-vis, EXAFS, and XANES. Importantly, the results show that the as-synthesized material will not suffer a permanent loss in porosity upon solvent removal. In addition to water, methanol, ethanol, and acetonitrile can also access the internal void of the dehydrated phase. 1. Introduction During the past decades, the direct, selective conversion of alkanes into higher valuable products has been subjected to an extensive research effort. 1,2 About 35 years ago, the first example of alkane activation was reported by Shilov’s group. 3 It was then observed that methane activation takes place in an aqueous solution containing K 2 PtCl 4 as catalyst. This so-called Shilov system did, however, suffer from a rather low turn-over number. Later on, a variety of homogeneous catalysts with improved activity and turn-over numbers have been developed using unsaturated electrophilic metal-organic complexes. 4,5 In par- ticular, complexes with Pt(II) coordinated to nitrogen containing organic ligands by electron donation have been extensively investigated. 6-8 Although more robust metal-organic complexes have been attained throughout the years, stability still remains a challenge, since their activity toward C-H bonds inevitably leads to a mutual destruction between the complexes. Another challenge addresses the fairly poor thermal stability of the complexes. Moreover, the constantly recurring problem of recovering homogeneous catalysts from the products also motivates the development of heterogeneous counterparts. Metal-organic frameworks (MOFs) constitute a relatively new class of materials. 9 The possibility to control the topology, geometry, and composition of the infinite framework predicts divergent applications. MOF type materials with different physical and chemical properties can indeed be constructed. 10 Materials with possible applications in the fields of molecular separation, 11 gas adsorption, 12 catalysis, 13-15 sensor technolo- gies, 16 magnetization, 17 luminescence, 18,19 proton conduction, 20 and semiconduction 21 have already been reported. Previously, we presented a controlled procedure for synthe- sizing a bimetallic MOF 22 with a structure composed of Pt(II) cis-coordinated to Cl and N in 2,2′-bipyridine-5,5′-dicarboxylate (BPDC). The Pt-organic part closely resembles the catalytically active sites in homogeneous counterparts developed for C-H activation. 6,23,24 In the bimetallic MOF, the Pt-organic parts that constitute the potentially catalytic sites are further connected through Gd ions, resulting in an extended framework (hereafter denoted as Pt/Gd-MOF) stable up to 350 °C. 22 Encouraged by these results, we have extended the development of materials containing the homogeneous counterpart. Herein, we present a new MOF with the same Pt-organic part as previous, but with Y as the corner stone (hereafter denoted as Pt/Y-MOF). Improvement of the thermal stability of the new Pt/Y-MOF from 350 to 400 °C is beneficial for the kinetics and provides higher flexibility in possible catalytic applications. Assuming that the catalytic properties of the above-mentioned homogeneous Pt complexes are due to the atom orientations and that the Pt sites are accessible, the present material may possess properties similar to those of the homogeneous counterparts for the direct conversion of methane. 7,24,25 The Pt sites in the present material are now fixed in the rigid lattice, avoiding self-destruction, thermal decomposition at low temperatures (present for the classical homogeneous com- * Corresponding author. Fax: +39011-6707855. E-mail silvia.bordiga@ unito.it. ² University of Oslo. ‡ Centre of Materials Science and Nanotechnology. § University of Turin. # Present address: Research & Development Division, Haldor Topsøe A/S, Nymøllevej 55 DK-2800 Lyngby. ⊥ Present address: ESRF, 6 rue Jules Horowitz, BP220, F-38043, Grenoble CEDEX, France. 21509 J. Phys. Chem. B 2006, 110, 21509-21520 10.1021/jp0634611 CCC: $33.50 © 2006 American Chemical Society Published on Web 10/06/2006