Coordination networks anion exchange

Water exchange on cationic lanthanide chelates can also be influenced by the nature of the counter-anions (170,171). Anions like halides, sulfate, nitrate, acetate, and fluoroacetate impose different order on the second coordination shell around the chelate by influencing the hydrogen bond network. Anions with a high charge density like CU and S04 can break up the hydrogen bond network between water molecules around the metal center and by that, slow down the water exchange rate of the inner shell water molecule (171). 

There are also carboxylates15 (Section 17-E-10), phosphates, catecholates, and oxalates. Most of the divalent iron oxalato compounds have a chain structure but the product of photoreduction of mononuclear [bipyH] [Feni(ojc)2(H20)2] gives a three-dimensional anionic polymeric network of [Fe2I(ox)3]2 1 and [Fen(bipy)3]2+ ions.16 Magnetic exchange typically occurs through the oxalate bridges.17 Six-coordinate iron(II) a-amino acid complexes are readily obtained from the reaction of the 4-coordinate Fe(mes)2(phen) and the protic amino add, AH, in THF 18... 

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