A titanium(IV) phosphate-phosphonate has been prepared from phosphonomethyliminodiacetic acid [H2O3PCH2N(CH2CO2H)(2), H(4)PMIDA]. It is poorly crystalline and can be formulated as [Ti-2(PO4)(H(2)PIMDA)(HPMIDA)(H2O)]. nH(2)O, Ti(PMIDA) [P:Ti = 1.5:1; n varies with relative humidity, RH]. Carboxylic acid groups are present in the interlayer region. Sorptiometry shows the material to be non-porous. Ti(PMIDA) reacts with n-alkylamines to form intercalates and is a proton conductor with conductivity strongly dependent on RH and temperature. Observed conductivities span nine orders of magnitude (sigma(360 K) = 8 x 10(-1) S cm(-1) for RH = 100%).