Investigation of Chromophoric Behavior of Water‐Soluble LaIII‐CuII Polynuclear Metallamacrocyclic 15‐MC‐5 Complex

The visible absorption spectrum of the water soluble polynuclear metallamacrocyclic La^III‐Cu^II complex La(H₂O)₃15‐MC_{Cu(II)Phalaha}‐5](Cl)₃ ( 1 ) based on α‐phenylalaninehydroxamic acid appears to be solvent‐ and ion‐sensitive. The copper(II) d–d transitions of the complex 1 dissolved in methanol, ethanol, water, dimethylformamide, dimethylsulfoxide, pyridine, and N‐methylpyrrolidone were studied. The chromophoric behavior of complex 1 was investigated in the presence of the Cl^–, Br^–, I^–, HSO₄^–, CO₃^2–, HCO₃^–, H₂PO₄^–, CN^–, SCN^–, and N₃^– anions. A considerable change of the d–d transition of the central copper(II) atom was observed for the strongly coordinating cyanide and azide anions. In the presence of HSO₄^–, the d–d intensity of copper(II) also decreased significantly. The molecular structure of La₂(H₂O)₇15‐MC_{Cu(II)Phalaha}‐5]₂(SO₄)₄ ( 2 ), obtained as result of the substitution of the coordinated water molecules in 1 by the SO₄^2– anions, was investigated by X‐ray crystallography.