Strong binding metal-chelating resins

A metal-chelating resin, comprising:

• (a) a compound represented by Formula (I):
• or a stereoisomeric form thereof or a salt thereof, wherein
• one of R1 and R2, and one of R3 and R4 are independently a protonated or deprotonated, substituted or unsubstituted 2-hydroxybenzyl moiety containing at least one linking group for covalently linking the compound of Formula (I) to an organic polymer resin, wherein the at least one linking group is represented by the formula —(CH2)x—NHR5 where x is 2 to 6, and R5 is independently hydrogen, methyl or ethyl, and the other one of R1 and R2, and the other one of R3 and R4 are independently a protonated or deprotonated, substituted or unsubstituted carboxyalkyl-containing moiety, wherein the alkyl group is a substituted or unsubstituted methylene group or a substituted or unsubstituted ethylene group optionally containing another linking group for covalently linking the compound of Formula (I) to the organic polymer resin;
• and
• Ra, Rb, Rc and Rd are hydrogen;
• and
• (b) an organic polymer resin comprising a styrenic polymer or copolymer having at least one complementary reactive functional group covalently linked with the at least one linking group of the compound represented by Formula (I).