K2[Ge(B4O9)].2H2O: a unique 3D alternating linkage mode of a B4O9 cluster and GeO4 unit in borogermanate with two pairs of interweaving double helical channels.

The first noncentrosymmetric potassium templated borogermanate, K(2)[Ge(B(4)O(9))].2H(2)O, has been solvothermally synthesized and characterized by IR, SEM, powder X-ray diffraction (PXRD), TGA, energy dispersive spectroscopy (EDS), single crystal X-ray diffraction, and second harmonic generation (SHG) activity, respectively. This compound crystallized in the monoclinic space group Cc with a = 6.793(1) A, b = 12.0699(3) A, c = 11.895(3) A, beta = 91.156(4) degrees, V = 975.1(4) A(3), and Z = 4. Interestingly, the structure possesses a unique 3D alternating linkage mode of B(4)O(9) clusters and GeO(4) units and contains two pairs of interweaving double helical channels with a 10-membered ring. In one, the right- and left-handed helices couple each other, and in the other, the left- and right-handed helices couple together. The compound exhibits distinct nonlinear optical (NLO) properties because it lacks a symmetric center. Furthermore, the framework of the title compound not only displays high thermal stability but also can be recoverable to a large degree during a dehydration-hydration cycle.