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A study of the dependence of the 1H, 31P and 13C NMR spectra of D2O solutions of piperidinomethylphosphinic acid (HL1) and piperazine-1,4-diylbis(methylene)bis(phosphinic acid)(H2L2) on the pH has indicated a strong acidity of the phosphinic groups and a low basicity of the nitrogen atoms. It is confirmed that the acids from zwitterions in aqueous solution and that the HL1 ring behaves similarly to the N-methylpiperidine ring. The stability constants of complexes formed with Mg2+, Ca2+, Pb2+, Co2+, Ni2+, Cu2+, Cd2+ and Zn2+ are lower than those of their acetic or phosphonic acid analogues. In the solid state, HL1·H2O exists as a zwitterion, monoclinic, space group P21/n, a= 6.884(2), b= 11.485(2), c= 11.994(2)A and β= 97.87(2)°. Two molecules are linked by hydrogen bonds into dimers which are connected by water molecules to form endless chains.

1-Alkyl and 1,8-dialkyl-1,4,8,11-tetraazacyclotetradecanes (alkyl = benzyl or methyl) were synthesised through cis -aminal of cyclam which was obtained by reaction of glyoxal and cyclam. The corresponding trans -aminal was synthesised from the respective linear tetraamine and glyoxal followed by cyclisation using 1,2-dibromoethane. The trans -aminal derivatives cannot be used for preparation of cyclam or its derivatives due to exceptional stability of the aminal bridge. The different reactivity of both cis - and trans -aminals is discussed on the basis of the X-ray structures determined for a series of the cyclam derivatives and could be explained by steric hindrance in the trans -aminals.

Phosphinic acid analogues of Gly-Gly, NH2CH2CONHCH2-P(R)O2H (R = Me, Ph, t-Bu), were synthesised by the active ester method from free aminomethylphosphinic acids purified on cation exchange resins. The crystal and molecular structure was determined for Gly–Gly(PPh)·H2O (R = Ph). The results point to similar bond parameters as were found for Gly–Gly and its phosphonic analogue Gly–Gly(P).