Novel molecular compounds containing carboxylic acid derivatives represented by general formula (I) or (II) as the constituent compound and exhibiting excellent performances in various technical fields including selective separation of useful substances, chemical stabilization, nonvolatilization, prolongation of release and powderization, wherein X is (CH.sub.2)n or p-phenylene; n is 0, 1, 2 or 3; R.sub.1 to R.sub.8 and R.sub.13 to R.sub.20 are each hydrogen, C.sub.1 -C.sub.6 alkyl, C.sub.2 -C.sub.4 alkenyl, phenyl optionally substituted with C.sub.1 -C.sub.6 alkyl, halogeno or C.sub.1 -C.sub.6 alkoxy; and R.sub.9 to R.sub.12 and R.sub.21 to R.sub.24 are each hydrogen, C.sub.1 -C.sub.6 alkyl, C.sub.2 -C.sub.4 alkenyl, C.sub.11 -C.sub.12 aralkyl or an alkali metal.