The first step in Procedure I involves sulfonating a ligand defined by the formula: ##STR33## wherein R4 to R6 and E are as defined above, provided that at least one of R4, R5 and R6 is an aryl group as defined above using SO3 in the presence of a strong inorganic mineral acid, such as sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, etc.