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It takes two to template: A cyclic hexaurea with four xanthene and two diphenyl ether units is predominantly formed by reaction of two diisocyanate molecules with two diamine molecules in the presence of chloride (see picture; green Cl, blue N, red O). The formation of a 1:2 complex with chloride was confirmed by X-ray analysis, solution NMR spectroscopy, and ESI-MS. The complexation constants were determined by microcalorimetry and UV spectrometry.
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Meshcheryakov et al. (2006) studied this question.
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