Synthesis and structure of the two-dimensional bimetallic oxide [H4tphz]3[{Zn2(tphz)(H2O)4}{Mo5O15(O3PCH2CH2PO3)}4] · 14H2O: the hydrothermal conversion of tetra-2-pyridylpyrazine to tetrapyrido [2,3-a:3′,2′-c:2″,3″-h:3‴,2‴-j]phenazine (tphz)

The hydrothermal reaction of (NH4)6Mo7O24 · 4H2O, ZnSO4 · 7H2O, tetra-2-pyridylpyrazine, ethylenediphosphonic acid, H2O and HF at 170 °C for 96 h yields yellow crystals of [H4tphz]3[{Zn2(tphz)(H2O)4}{Mo5O15(O3PCH2CH2PO3)}4] · 14H2O (1 · 14H2O) (tphz=tetrapyrido[2,3-a:3′,2′-c:2″,13″-h:3‴,2‴-j]phenazine (tphz)). The structure of 1 consists of two-dimensional networks constructed from chains of {Mo5O15(O3PR)2}4− clusters tethered through the ethylene bridges of the diphosphonate ligands, which are in turn crosslinked through the {Zn2(tphz)(H2O)4}4+ subunits. This connectivity generates intralamellar cavities which are occupied by the tetraprotonated H4tphz4+ cations. A curious feature of the chemistry is the hydrothermal conversion of the tetra-2-pyridylpyrazine starting material to tphz.