The new alkalimetal-hydrogenbis(carbonato)-bis(carbonato)complexes with penta-coordinated zinc atoms, NaA2{Zn2[H(CO3)2](CO3)2(H2O)2} with A = Kor Rb, crystallize in the monoclinic system, P21/n (no. 14), Z = 2 with a = 1057,9(1), b = 1102,2(1), c = 514,9(1) pm, β = 92,94(1)°, VEZ = 599,6(2) · 106 pm3, R = 0,052, Rw = 0,029 for the potassium compound and with a = 1068,2(2), b = 1131,6(4), c = 518,6(1) pm, β = 92,07(1)°, VEZ = 626,4(4)·106 pm3, R = 0,050, Rw = 0,028 for the rubidium compound. These compounds are the first to be structurally characterized with a simultaneous presence of discrete [H(CO3)2]3-and CO32- anions.
The crystal structure of the isostructural compounds contains two-dimensional infinite {Zn2[H(CO3)2](CO3)2(H2O)2} layers parallel [1 0 1] with zinc coordinated in a slightly distorted trigonal-bipyramidal geometry. The layers are held together by hydrogen bonds from water molecules to oxygen atoms of the carbonato groups in adjacent layers. Potassium or rubidium atoms are located between the layers, and sodium atoms in smaller vacancies within the layers. The hydrogen bond of the [H(CO3)2]3- anion is very short, O···O: 247,4(2) pm (K) and 246,9(5) pm (Rb). The carbonate groups in both compounds exhibit significant deviations from D3h symmetry in accordance with the vibrational modes observed in the IR spectra. The thermal behaviour of the potassium compound is also reported.
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