Initially, we therefore looked into the decomplexation of the sensor with polyP8, which is currently the longest monodisperse polyP available by synthesis. Also shorter polyphosphates are accessible in monodisperse form through chemical synthesis (see SI section 12). 26 Addition of polyP8 to complex 6 (in 10 mM HEPES buffer at pH = 7.4) led to a gradual decrease of the absorption peaks at 288 nm, 300 nm and 356 nm (Fig. ). In case of complex 7, the absorption peaks at 254 nm, 284 nm and 351 nm also decreased while absorption increased at 317 nm with increasing polyP8 concentration (Fig. ). Interestingly, the decrease in absorption intensities was much higher with non-chlorinated 7 compared to chlorinated 6. The structures of complexes 6 and 7 are tentatively assigned to be square planar, but we could not obtain crystal structures of the compounds. The very different behaviour might be a result of distortions of the geometry based on steric constraints potentially exerted by the chlorine atom.