Multifunctional lanthanum tetraphosphonates: Flexible, ultramicroporous and proton-conducting hybrid frameworks

A new flexible ultramicroporous solid, La(H5DTMP)center dot 7H(2)O (1), has been crystallized at room temperature using the tetraphosphonic acid H8DTMP, hexamethylenediamine-N,N,N',N'-tetrakis(methylenephosphonic acid). Its crystal structure, solved by synchrotron powder X-ray diffraction, is characterised by a 3D pillared open-framework containing 1D channels filled with water. Upon dehydration, a new related crystalline phase, La(H5DTMP) (2) is formed. Partial rehydration of 2 led to La(H5DTMP)center dot 2H(2)O (3). These new phases contain highly corrugated layers showing different degrees of conformational flexibility of the long organic chain. The combination of the structural study and the gas adsorption characterization (N-2 and CO2) suggests an ultramicroporous flexible framework. NO isotherms are indicative of a strong irreversible adsorption of NO within the pores. Impedance data indicates that 1 is a proton-conductor with a conductivity of 8 x 10(-3) S cm(-1) at 297 K and 98% of relative humidity, and an activation energy of 0.25 eV.