Synthesis, Structural, Magnetic, and Redox Properties of Asymmetric Diiron Complexes with a Single Terminally Bound Phenolate Ligand. Relevance to the Purple Acid Phosphatase Enzymes

New asymmetrical ligands (H2L) have been synthesized to provide both a bridging and a terminal phenolate to a pair of iron ions in order to mimic the binding of a single terminal tyrosinate at the diiron center of the purple acid phosphatases. H2L1 is 2-[(bis(2-pyridylmethyl)amino)methyl]-6-[((2-pyridylmethyl)(2-phenol)amino)methyl]-4-methylphenol and H2L‘1 and H2L2 are obtained by replacing the 2-phenol group by the 5-nitro-2-phenol and the 6-methyl-2-phenol residues, respectively. A series of mixed valence diiron complexes [FeIIFeIIIL(X)2](Y) have been obtained where (X)2 is the dianion of m-phenylenedipropionate or (H2PO4)2 and Y = BPh4 or PF6 (L = L1, 1a (X)2 = mpdp, Y = BPh4, 1b:  (X)2 = (OAc)2, Y = BPh4, 1c:  (X)2 = (OBz)2, Y = BPh4, 1d:  (X)2 = (H2PO4)2, Y = PF6; L = L‘1:  1‘a (X)2 = mpdp, Y = BPh4; L = L2:  2c:  (X)2 = (OBz)2, Y = BPh4, 2d:  (X)2 = (H2PO4)2, Y = PF6. Diferric complexes have been obtained also either by direct synthesis or by iodine oxidation of the mixed valence precursor (L = L1,...