New metastable hybrid phase, Zn2(OH)2(C8H4O4), exhibiting unique oxo-penta-coordinated Zn(II) atoms

The metastable phase (phase 1) Zn(OH)2(tp)2 (tp = C8H4O42−) was found to be an intermediate forming during the hydrothermal synthesis of Zn3(OH)4tp (phase 2). Its structure has been determined ab initio from synchrotron powder diffraction data and refined with the Rietveld method: space group P21/c, a = 3.48856(2) Å, b = 5.84645(2) Å, c = 22.1331(1) Å, β = 103.46(1)°, Dx = 2.488 g/cm3, Rp = 0.10, RB = 0.095 (402 independent reflections). The structures of the two analogues were compared. Whereas a mixed coordination of the zinc atoms was found in phase 2, phase 1 exhibits only penta-coordinated Zn(II). Moreover, different optical properties were observed, Zn2(OH)2(tp) showing photoluminescence at 378 nm under λex = 316 nm.

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