Structural chemistry of organically templated transition metal phosphite chlorides, [BH2][M(H2PO3)2Cl2] (B = diamine, M = Mn–Ni, Cd) as new analogs of “hydroselenite halides”

Following the previously reported (enH₂)[Co(H₂PO₃)₂Cl₂] (enH₂ = ethylenediammonium cation), we successfully prepared its analogs with other divalent transition metal cations: Mn²⁺, Fe²⁺, Ni²⁺, and Cd²⁺. These compounds are isostructural to each other and the archetypic hydroselenites, (enH₂)[M(HSeO₃)₂X₂]. Despite evident similarities, some essential differences are observed between hydroselenites and hydrophosphites, both in chemistry and in structural details. Due to smaller size of H₂PO₃⁻ relative to HSeO₃⁻, only chloride phosphites could be prepared; the reducing capacity of H₂PO₃⁻ permits preparation of Fe^II compound but not that of Cu^II. A single attempt to introduce piperazinediium cation instead of ethylenediammonium results in formation of (pipH₂)[Co(H₂PO₃)₂Cl₂] with a structure different from (pipH₂)[Cd(HSeO₃)₂Cl₂]. Another serendipitous product is the 1-methylpiperazinediium derivative, (mpipH₂)₂[Co(H₂PO₃)₂I₃][H(H₂PO₃)₂], which features a yet unique complex hydrogen-bonded network.