Na-5[B2P3O13] was first prepared by high temperature synthesis (T-max = 780 degrees C) and was characterized by X-ray single crystal investigations recently. We have now succeeded in the hydrothermal synthesis of the compound and obtained single-phase products at 150 degrees C after 1-2 days. A microwave-assisted synthesis takes only 2 min to transform a solid mixture of berate and phosphate hydrates into the crystalline title compound. Pure Na-5[B2P3O13] melts at 747 degrees C and solidifies during cooling by formation of a homogeneous glass. (C) 1998 academic Press.