Na1.5rb0.5po3f Center Dot H2o: Synthesis, Properties, And Stepwise Reconstruction Of The Hydrogen Bond Network

We report a new DUV transparent (<200 nm) noncentrosymmetric Na1.5Rb0.5PO3F center dot H2O compound crystallizing in the Pmn2(1) space group. This compound exhibits the second largest birefringence in the monofluorophosphate family, Delta n(obv.) = 0.04 at 546 nm, which is attributed to the nearly uniform alignment of the P-F bonds. The SHG response is observed to be 0.55 x KDP at 1064 nm. More interestingly, the precise substitution of NH4+ with Na+/Rb+ cations in the well-known structure (NH4)(2)PO3F center dot H2O leads to a stepwise reconstruction of the hydrogen bond networks, which eventually alters the crystal symmetry and the optical properties.