The novel compounds of the formulae Ia and Ib ##STR1## in which the radicals R are identical or different and are a group of the formula II ##STR2## in which X is a direct bond, methylene, ethylene or a group ##STR3## and Y is C.sub.1 -C.sub.8 alkyl, R.sub.1 and R.sub.2 independently of one another are C.sub.1 -C.sub.18 alkyl, C.sub.5 -C.sub.12 cycloalkyl, C.sub.5 -C.sub.7 cycloalkyl which is substituted by C.sub.1 -C.sub.4 alkyl, or are phenyl or C.sub.7 -C.sub.10 phenylalkyl, and R.sub.2 is additionally hydrogen, are suitable for stabilizing organic material against thermal, oxidative or actinic degradation.