Abstract: Hydroxamic acids and hydroxamic acid ethers I and II ##STR1## where Z.sup.1 and Z.sup.2 are --NH --OY, --NR.sup.1 --OY or --OX, where in the case of (I) at least one of Z.sup.1 or Z.sup.2, and in the case of (II) Z.sup.1 is --NH --OY or --NR.sup.1 --OY, andR.sup.1 is C.sub.1 -C.sub.18 -alkyl,X is hydrogen, alkali metal, ammonium or substituted ammonium, andY is hydrogen, alkali metal, ammonium, substituted ammonium or C.sub.1 -C.sub.18 -alkyl, andL is a C.sub.1 -C.sub.100 linker which can also carry oxygen and nitrogen functional groups,with the exception of N,N-bis(carboxymethyl)-2-aminoacetohydroxamic acid.