Efficient guest exchange: The organic zeolite analogue TPP⋅x(THF) (x=0.35–0.65) takes up I2 quickly when exposed to iodine vapor. The previously colorless crystals (a) color at the ends (b), and after 1–2 days the iodine has permeated all the way through the crystal (c). The conductivity values of the TPP⋅y(I2) crystals are of the same order as those of elemental I2. TPP=tris(o‐phenylenedioxy)cyclotriphosphazene.

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Macroscopically polar crystals of an organic zeolite, tris(o‐phenylenedioxy)cyclotriphosphazene, are obtained by partial guest exchange of included THF molecules with nonlinear optical molecules, which enter the channels via a mechanism of surface recognition (4‐amino‐4′‐nitrobiphenyl partially (left) and fully (right) stained crystals are shown in the Figure).

Application of ultrasound and ball milling produces micrometer‐sized crystallites of tris‐(o‐phenylenedioxy)‐cyclotriphosphazene (TPP) that show zeolite‐like reversible sorption of I2 and CH3I (methyl iodide). The thermal stability of open‐pore TPP is improved by partial loading with pyrazine. The sorption properties of open‐pore TPP are investigated by the 131I radioactive tracer method. Comparison with activated charcoal (ACC) shows that TPP has a higher sorption efficiency for I2 dissolved in water than ACC. In the case of a humid gaseous source of CH3I also, TPP exhibits better sorption properties than ACC. Partial loading of open‐pore TPP by pyrazine increases its thermal stability by 50 °C and the binding properties for retaining CH3I are also improved. Force‐field calculations show a difference of ΔE ≈ 20 kJ mol–1, making the open‐pore system less stable than the apohost.

The mechanism of insertion of p-nitroaniline (PNA) and its diffusion behavior in channels of the hexagonal host structure of tris(o-phenylenedioxy)cyclotriphosphazene (TPP) was investigated by means of molecular modeling tools. Strong preferential sites in the bulk were found to be due to pi-pi and NH-pi interactions between PNA and channel walls of TPP. MD simulations showed that diffusion can be characterized by jumps from one site to the next, occurring mainly because of the dynamic flexibility of the host structure. Calculations of host-guest interactions between the TPP surface and PNA approaching the entrance of channels with its terminal H2N-first or O2N-first revealed that the H2N-first insertion is clearly preferred. Preferential insertion of PNA is found to be the reason for polar effects, observed experimentally. Because of a distinct guest-host recognition at the surface, guest-guest interactions were found to have a minor influence on polarity.