A series of lanthanide(III) complexes formulated as M[Ln(Hdo3ap)]center dot xH(2)O (M = Li or H and Ln = Tb, Dy, Er, Lu, and Y) with the monophosphonate analogue of H(4)dota, 1,4,7,10-tetraazacyclododecane-1,4,7-triacetic-10-methylphosphonic acid (H(5)do3ap), was prepared in the solid state and studied using X-ray crystallography. All of the structures show that the (Hdo3ap)(4-) anion is octaclentate coordinated to a lanthanide(III) ion similarly to the other H(4)dota-like ligands, i.e., forming O-4 and N-4 planes that are parallel and have mutual angle smaller than 3 degrees. The lanthanide(III) ions lie between these planes, closer to the 04 base than to the N4 plane. All of the structures present the lanthanide(III) complexes in their twisted-square-antiprismatic (TSA) configuration. Twist angles of the pendants vary in the range between -24 and -30 degrees, and for each complex, they lie in a very narrow region of 1 degrees. The coordinated phosphonate oxygen is located slightly above (0.02-0.19 angstrom) the O-3 plane formed with the coordinated acetates. A water molecule was found to be coordinated only in the terbium(III) and neodymium(III) complexes. The bond distance Tb-O-w is unusually long (2.678 angstrom). The O-Ln-O angles decrease from 140 degrees (Nd(III)] to 121 degrees [Lu(III)], thus confirming the increasing steric crowding around the water binding site. A comparison of a number of structures of Ln(III) complexes with DOTA-like ligands shows that the TSA arrangement is flexible. On the other hand, the SA arrangement is rigid, and the derived structural parameters are almost identical for different ligands and lanthanide(III) ions.