Crystal structures of Mg2+, Ba2+ and Cs+ exchanged K–Na–ETS-4

Microporous titanosilicate K–Na–ETS-4 has been synthesized and exchanged to Mg2+, Ba2+, and Cs+ forms. The structures were determined from single crystal X-ray diffraction data and the compositions were confirmed by energy dispersive X-ray spectroscopy. The inclusion of the Ba2+ caused a substantial framework contraction and the obtained data suggested a change from five- to six-coordination of the titanium atom belonging to the titanosilicate bridging unit. Both Ba2+ and Cs+ ions substitute water molecules and charge compensations ions, while Mg2+ prefers to occupy the position of Na+. All structures were refined in space group Cmmm having stoichiometric formulas: K3.25Na2.12H3.63Si12Ti5O38(OH)·10.64H2O; K2.63Mg1.44H3.49Si12Ti5O38(OH)·7.92H2O; K1.18Na1.20Cs4.01H2.61Si12Ti5O38(OH)·7.12H2O and Ba4.31H0.39Si12Ti5O39·4.52H2O. The obtained results may help understanding the cation exchange, thermal and gas separation properties of ETS-4.

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► Ion exchange of the microporous titanosilicate ETS-4.
► Structure solution from single crystal data.
► Framework distortion and replacement of water molecules.
► Coordination change of the titanium atom.