The crystalline cadmium phenylphosphonates Cd(O 3 PPh) · H 2 O (1), Cd(HO 3 PPh) 2 (2), and Cd(HO 3 PPh) 2 (H 2 O 3 PPh) (3) can be synthesized in solid state reactions by grinding together cadmium acetate with respective equivalents of phenylphosphonic acid. The phosphonates (2) and (3) were not obtained by any other synthesis method so far. The determination of the crystal structure of the new compounds (2) and (3) based on the powder X-ray diffraction (PXRD) data is reported. The milling reactions were investigated using in situ synchrotron PXRD. Based on these data, an identification of intermediates and a detailed analysis of the underlying mechanisms was possible.Unlike for the related class of metal organic frameworks (MOFs) the use of alternative synthetic routes like mechanochemistry is scarce. [18][19][20] Recently, in situ methods were developed to investigate milling syntheses to provide the necessary data for a thorough mechanistic study. 21-24 Fig. 1 Reaction scheme for the syntheses of the products (1), (2) and (3); OAc = (O 2 CCH 3 ) -·Here, we present the mechanochemical synthesis of three cadmium phenylphosphonates; the cadmium monophenylphosphonate Cd(O 3 PPh) · H 2 O (1) (Ph = C 6 H 5 ) 25 and two novel structures (1:2 and 1:3) (Figure 1). The structures of the new compounds Cd(HO 3 PPh) 2 (2) and Cd(HO 3 PPh) 2 (H 2 O 3 PPh) (3) were determined from powder X-ray diffraction (PXRD) data. Compound (2) contains two monodeprotonated phenylphosphonate ligands. The compound (3) contains a further neutral J o u r n a l N a me , [ y e a r ] , [ v o l . ] , 1-9 | 1