A novel oxonitridophosphate, Ba19P36O6+xN66-xCl8-x (x approximate to 4.54), has been synthesized by heating a multicomponent reactant mixture consisting of phosphoryl triamide OP(NH2)(3), thiophosphoryl triamide SP(NH2)(3), BaS, and NH4Cl enclosed in an evacuated and sealed silica glass ampule up to 750 degrees C. Despite the presence of side phases, the crystal structure was elucidated ab initio from high-resolution synchrotron powder diffraction data (lambda = 39.998 pm) applying the charge flipping algorithm supported by independent symmetry information derived from electron diffraction (ED) and scanning transmission electron microscopy (STEM). The compound crystallizes in the cubic space group Fm (3) over barc (no. 226) with a = 2685.41(3) pm and Z = 8. As confirmed by Rietveld refinement, the structure comprises all-side vertex sharing P(O,N)(4) tetrahedra forming slightly distorted 3(8)4(6)8(12) cages representing a novel composite building unit (CBU). Interlinked through their 4-rings and additional 3-rings, the cages build up a 3D network with a framework density FD = 14.87 T/1000 angstrom(3) and a 3D 8-ring channel system. Ba2+ and Cl- as extra-framework ions are located within the cages and channels of the framework. The structural model is corroborated by P-31 double-quantum (DQ) /single-quantum (SQ) and triple-quantum (TQ) /single-quantum (SQ) 2D correlation MAS NMR spectroscopy. According to P-31{H-1} C-REDOR NMR measurements, the H content is less than one H atom per unit cell.