Preparation and crystal structure of the first mixed alkalimetal hydrogencarbonates NaA(2)[H(CO3)(2)]center dot 2H(2)O with A=K, Rb

The new hydrogencarbonates NaK2[H(CO3)(2)]. 2H(2)O (Pnma, a = 934.07(13) pm, b = 789.31(10) pm, c = 1142.1(5) pm, V-EZ = 842.0(4). 10(6) pm(3), Z = 4, R1 (I greater than or equal to 2 sigma(I)) = 0.023, wR2 = 0.066 for 989 reflections) and NaRb2[H(CO3)(2)]. 2H(2)O (Pnma, a = 948.24(11) pm, b = 811.37(9) pm, c = 1189.0(2) pm, V-EZ = 914.8(2). 10(6) pm(3), Z = 4, R1 (I greater than or equal to 2 sigma(I)) = 0.031, wR2 = 0.077 for 1063 reflections) were prepared from aqueous solutions. The crystal structures were determined. The isostructural compounds contain dimeric, non centrosymmetric [H(CO3)(2)](3-) anions. In NaK2[H(CO3)(2)]. 2H(2)O a short hydrogen bond (d(O ... O) = 246.1(2) pm) with an asymmetric potential was detected. In NaRb2[H(CO3)(2)]. 2H(2)O a hydrogen bond with symmetric potential (d(O ... O)= 247.8(5) pm) can be assumed. The IR-spectra of NaK2[H(CO3)(2)]. 2H(2)O and Na-3[H(CO3)(2)]. 2H(2)O are compared.