This communication reports the synthesis and X-ray structure of the first mixed-valence (FeZnII)-Zn-III complex containing the Fe-III(mu-OH)Zn-II structural unit. Based on the structure, physicochemical solution studies, and the catalytic properties toward the hydrolysis of the diester 2,4-bis(dinitrophenyl)phosphate (BDNPP), it is proposed that complex 1 employs a hydrolytic mechanism similar to that proposed for red kidney bean purple acid phosphatase, including a nucleophilic attack by the terminal, Fe-III-bound hydroxide and the concomitant release of 2,4-dinitrophenolate. Furthermore, it is demonstrated that the mu-hydroxo group in the {Fe-III(mu-OH)(mu-ROPO3)Zn-II} intermediate is unable to hydrolyze the monoester 2,4-dinitrophenylphosphate (DNPP), which suggests that the mu-hydroxo group is a significantly poorer nucleophile than the terminally Fe-III-bound OH- group.