In the last years, porous organic-inorganic hybrid materials have fascinated by the potential technological application related to the combination of hydrophobic organic layers and hydrophilic inorganic ones [1]. Recently, a new class of microporous hybrid organic-inorganic alumino-silicates materials (Eni Carbon Silicate - ECS) has recently been synthesized at the Eni laboratories [2]. The crystal structure solution of ECS-2, a sodium aluminosilicate member of this new family, is here reported. The structural model was achieved by combining information obtained by high resolution X-ray Powder Diffraction (XRPD), NMR spectroscopy and high Resolution Transmission Electron Microscopy (HRTEM).²⁹Si MAS NMR spectroscopy confirmed that the organic group was covalently bounded to the inorganic scaffolding, while ¹³C MAS NMR clearly showed the presence of ethanol molecules, likely deriving from the hydrolysis of the organic precursor, stocked in the pores of ECS-2. HRTEM images of ECS-2 showed alternating layers suggesting that the organic layer may be stacked to the inorganic one (Fig. 1a). The XRD pattern of as-synthesized ECS-2, collected on the beam line ID-31, at ESRF in Grenoble (λ = 0.80175(2)Å), has been indexed using a monoclinic unit cell with parameters a = 7.908, b = 19.5339, c = 7.8758 Å and ß = 108.72°, and the analysis of the systematic absences indicated the P2₁/n as the possible space group. The structural model of ECS-2 has been achieved by application of direct methods and can be rationalized by the stacking of alumino-silicate layers held together by phenylene groups (Fig. 1b), in agreement with the microscopy analysis. This scaffolding is characterized by the presence of large cages where the ethanol molecules find place (Fig. 1c); however, the six phenylene groups hampers the access to these cages, allowing the structure of ECS-2 to be classified as clathrate-like.

[1] B.D. Hatton, K. Landskron, W.J. Hunks, M.R. Bennet, D. Shukaris, D.D. Perovic, G.A. Ozin, Materials Today 2006, 9, 22-31

[2] A. Carati, C. Rizzo, U. Diaz Morales, G. Bellussi, S. Zanardi. W.O. Parker, Jr., R. Millini, BE 1,016,877, assigned to Eni S.p.A.

Fig. 1. a) High resolution transmission electron micrograph of ECS-2; b) Polyhedral structure of ECS-2 (dark gray small spheres are atoms of sodium); c) Six phenylene cage.

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