The chemistry of metal phosphonates has been of increasing interest during the past two decades, owing to their practical applications as ion exchangers, catalysts and sensors. Great efforts have been devoted to the metal diphosphonates, by modifying the organic tether (R) of R(PO₃H₂)₂, to explore new materials with large pores and interesting functions. The template effect on directing the formation of different metal diphosphonate structures, however, has not been well documented. We present here the syntheses and structures of eleven M-hedp compounds, where M = Cu, Fe, Ni; hedp = 1-hydroxyethylidenediphosphonate. The influences of templates on the final products are discussed.