Modular Assembling of [Zr(C 2 O 4 ) 4 ] 4- and [DabcoH 2 ] 2+ Units in Supramolecular Hybrid Architectures Including an Open Framework with Reversible Sorption Properties (Dabco ) 1,4-Diazabicyclo[2. 2. 2]octane) Franck The ´tiot, Carine Duhayon, Thengarai S. Venkatakrishnan, and Jean-Pascal Sutter* Laboratoire de Chimie de Coordination du CNRS, UniVersite ´ Paul Sabatier, 205 route de Narbonne, 31077 Toulouse, France ReceiVed October 5, 2007; ReVised Manuscript ReceiVed February 28, 2008 ABSTRACT: An emerging trend toward development of metal-organic frameworks (MOF) consists in using preformed complexes as building blocks able to assemble via coordination chemistry and/or charge-assisted H-bonding. Within this framework and depending only on the experimental conditions, reactions of the [Zr(C 2 O 4 ) 4 ] 4- anion with the [DabcoH 2 ] 2+ dication (Dabco ) 1,4-diazabicyclo[2. 2. 2]octane) selectively afford the compounds {K 2 (DabcoH 2 )[Zr(C 2 O 4 ) 4 ]} · 6.5H 2 O(1), {(DabcoH 2 ) 2 [Zr(C 2 O 4 ) 4 ]} · 3H 2 O(2), {(DabcoH 2 ) 2 [Zr(C 2 O 4 ) 4 ]} · 5.5H 2 O(3), or {K 2 (DabcoH 2 ) 2 [Zr 2 (C 2 O 4 ) 7 ]} · 6H 2 O(4). Three association schemes exhibiting drastically different network topologies have been characterized ranging from 1D to 3D; the fourth involving the in situ generated bimetallic {Zr 2 (C 2 O 4 ) 7 } 6- moiety. For all four compounds, selective synthetic processes have been developed. In addition, compound 1 exhibits an open framework able to release solvates without collapsing. Besides the reversible sorption of small molecules like EtOH and MeCN, the open framework 1 was found to adsorb CO 2 at ambient temperature and pressure (ca. 30 cm 3 of gas g -1 at 298 K), whereas its propensity to take up H 2 O from air is low. Introduction Within the area of supramolecular chemistry, the design and synthesis of open frameworks with remarkable structural, chemical and physical properties have drawn an increasing interest over the past few years. Among these, the 3D coordina- tion polymers known as metal-organic frameworks (MOF) are the most investigated. The interest for supramolecular frame- works is not only for their prospective applications as functional materials 1 but also for their intriguing and diverse molecular topologies and assembling processes. 2–12 The approach toward development of this kind of functional architectures consists in using molecular building blocks able to assemble via coordina- tion chemistry and/or H-bonding. Compared to the “classical” inorganic materials, this flexible approach exhibits a rational and more resourceful design methodology to achieve supramo- lecular architectures with specifically tailored properties. Given the diversity and versatility of building units (inorganic, organometallic, or organic) potentially available and their intrinsic properties, such materials can display an extensive variety of customized physical or chemical properties, such as gas storage, 13–15 sensors, 16 sorption and separation processes, 17,18 catalysis, 16 ion-exchange, 20 luminescence, 21 guest-driven mag- netic behaviors, 22–25 etc. 5,26 Until now, the widely used route to form a metal-organic framework has consisted of the direct assembly of a metal ion with a bridging ligand. The resulting network relies on the formation during the association process of the so-called secondary building units. In contrast, the use of a preformed coordination compound as a molecular building block remains hardly considered for the construction of porous frameworks. 16,21,27–40 However, the efficiency of this latter route has already been demonstrated in the conception of numerous molecule-based materials like bimetallic magnets. 41,42 Typi- cally, such a building block consists of a metal center surrounded by ligands that are able to connect to a second building unit or metal ion by available functional groups. This may take place either via covalent (metal-ligand) or hydrogen bonds. As a result, the use of such preformed building blocks selected according to their geometry and linking abilities allows to design a node of the network and consequently the topology of the final supramolecular assembly. In this context, archetypal examples of building blocks we have investigated are the pseudotetrahedral shaped coordination complexes [M(C 2 O 4 ) 4 ] 4- (M ) Zr(IV), U(IV), C 2 O 4 2- ) oxalate) that display four potential oxalate linkers. This geometry is in favor of obtaining high-dimensional architectures and is efficient at spacing the associated units. In a previous work, the association of [M(C 2 O 4 ) 4 ] 4- building units with M 2+ metal ions led us to the genesis of original supramolecular nanoporous architectures in which the 3D heterometallic frameworks are developed through the linkages between the oxygen atoms of the [M(C 2 O 4 ) 4 ] 4- units and the M b 2+ metal ions. 27,36,37 Considering that these oxygen atoms may also act as efficient H-bond acceptors, we have explored the possibility to develop hydride architectures by assembling this anionic coordination complex with appropri- ate organic cations through charge-assisted H-bonds. Within this latter approach, we have recently reported a series of architec- tures constructed by combination of [Zr(C 2 O 4 ) 4 ] 4- with different cationic N-H donors able to act as bridges. 43 Depending on the features of the organic modules (geometry, dimensions) and the nature of the donor groups, assembling patterns ranging from 1D to 3D have been observed. Taking into account these observations, we have considered the association of [Zr(C 2 O 4 ) 4 ] 4- with {DabcoH 2 } 2+ (Dabco ) 1,4-diazabicyclo[2. 2. 2]octane) with the aim of generating an open framework. We have observed that under selective experimental conditions, the assembling processes of the [Zr(C 2 O 4 ) 4 ] 4- anion with the [DabcoH 2 ] 2+ dication singularly differ leading exclusively to either compounds {K 2 (DabcoH 2 )- [Zr(C 2 O 4 ) 4 ]} · 6.5H 2 O(1), {(DabcoH 2 ) 2 [Zr(C 2 O 4 ) 4 ]}. 3H 2 O(2), {(DabcoH 2 ) 2 [Zr(C 2 O 4 ) 4 ]} · 5.5H 2 O(3) or {K 2 (DabcoH 2 ) 2 [Zr 2 - (C 2 O 4 ) 7 ]} · 6H 2 O(4). For all four compounds, selective synthetic * Corresponding author. E-mail: sutter@lcc-toulouse.fr. Web address: http:// www.lcc-toulouse.fr/lcc/accueil.php3?lang)en. Fax: (33) 561 55 30 03. CRYSTAL GROWTH & DESIGN 2008 VOL. 8, NO. 6 1870–1877 10.1021/cg700971n CCC: $40.75  2008 American Chemical Society Published on Web 05/13/2008