Di-maltol-polyamine ligands to form heterotrinuclear metal complexes: solid state, aqueous solution and magnetic characterizationElectronic supplementary information (ESI) available. CCDC 901272-901274. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c3dt32130d

• Main Authors: Benelli, Cristiano, Borgogelli, Elisa, Formica, Mauro, Fusi, Vieri, Giorgi, Luca, Macedi, Eleonora, Micheloni, Mauro, Paoli, Paola, Rossi, Patrizia
• Format: Article
• Language: English
• ISSN: 1477-9226; 1477-9234
• DOI: 10.1039/c3dt32130d

The binding properties of the two ligands (L) N , N ′-bis[(3-hydroxy-4-pyron-2-yl)methyl]- N , N ′-dimethylethylendiamine (Malten) and 4,10-bis[(3-hydroxy-4-pyron-2-yl)methyl]-1,7-dimethyl-1,4,7,10-tetraazacyclododecane (Maltonis) towards M( ii ) transition metal ions (M( ii ) = Cu( ii ) for Malten and Co( ii ) for Maltonis, respectively), were investigated in aqueous solution. Each compound contains two 3-hydroxy-2-methyl-4-pyrone units (Maltol) symmetrically spaced by a different polyamine fragment. The formation of only mononuclear complexes was detected and the main species present in a wide range of pH is the neutral [M( ii )(H −2 L)] complex. This is able to stabilize one hard M( iii ) metal ion such as Gd( iii ) and Y( iii ), giving rise to the formation of new hetero-trinuclear complexes of M( ii )-M( iii )-M( ii ) sequence. The trinuclear species having the formula {M( iii )[M( ii )(H −2 L)] 2 } 3+ (M( ii ) = Cu( ii ) and M( iii ) = Y( iii ) or Gd( iii ) for Malten and M( ii ) = Co( ii ) and M( iii ) = Gd( iii ) for Maltonis) are also formed in a wide range of pH, including pH = 7 and can be isolated in high yield as a perchlorate salt. The crystal structures of all the studied hetero-trinuclear species highlight that such systems are formed thanks to the synergy between the different stereochemical requirement of the transition metal (Cu( ii ) or Co( ii )) and the different donor atoms set of the ligands which preorganize the maltol units for the binding of the hard M( iii ) metal, otherwise difficult to bind in water, through L/M( ii )/M( iii ) self-assembling. The magnetic properties of the hetero-trinuclear spin systems were investigated; in the M( ii )-Gd( iii )-M( ii ) species, Gd( iii ) interacts with the two 3d ions of this class of compounds by similar coupling mechanism. Two new transition metal complex units obtained with the suitable di-maltol-polyamine ligand are able to stabilize M( iii ) ions, such as Gd( iii ) and Y( iii ), in water to form a M( ii )-M( iii )-M( ii ) sequence.