Synthesis and structural characterization of two open-framework zinc phosphites with (3,4)-connected networks

Two new organically templated zinc phosphites, [H2dmpip][Zn3(HPO3)4] (1) and [HMedmpip][Zn3(HPO3)4] (2), where dmpip = 2,6-dimethyl-piperazine and Medmpip = N-methyl-2,6-dimethyl-piperazinium, have been synthesized and structurally characterized. Note that the new Medmpip2 + template in 2 is generated from in situ N-methylation reaction between CH3OH and the dmpip amine precursor, which is used to serve as template in 1. Such direct N-methylation transformation is unique, and quite different from conventional Eschweiler–Clarke methylation in which an excess of formic acid and formaldehyde was required. Both compounds are constructed from strictly alternating ZnO4 and HPO3 units, and possess different (3,4)-connected interrupted frameworks with intersecting 8-, 10- and 12-ring channels (for 1), and 8-, 12-ring channels (for 2), respectively. The occurrence of helical channels in the open structure of 1, and fascinating hydrogen-bonded helices between the host inorganic chains and guest organic templates are also noteworthy.