Showing papers by "Vieri Fusi published in 2013"
TL;DR: 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.
Abstract: 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−2L)] 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−2L)]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.
18 citations
TL;DR: Potentiometric and UV-Vis solution studies as well as four crystal structures of metal-complexes support the conclusion that Cu(II) forms only mononuclear species with both ligands, thus providing information for the choice of a suitable metal to preorganize side-arms on a polyamine macrocyclic scaffold.
Abstract: The binding properties of 4,10-bis[(3-hydroxy-4-pyron-2-yl)methyl]-1,7-dimethyl-1,4,7,10-tetraazacyclododecane (L1) and 4,10-bis[(2-hydroxy-5-nitrophenyl)methyl]-1,7-dimethyl-1,4,7,10-tetraazacyclododecane (L2) towards Cu(II) and Co(II) transition metal ions in aqueous solution and in the solid state were studied and compared. Each system consists of a cyclen scaffold bearing two different side-arms; the role of the two transition metal ions to involve side-arms in coordination was investigated. Each metal ion is coordinated in a similar way by both ligands although a different side-arm arrangement occurs. The Me2Cyclen base is always involved in the coordination of the transition metal cation with the four amine functions; both side-arms bind Co(II) while only one of them binds Cu(II). As a consequence, Co(II) forms only mononuclear species with both ligands; the main [Co(H−2L)] species exhibits both side-arms on the same part with respect to the macrocyclic plane. In the case of L1, this allows the formation of an electron rich area, formed by the four converging oxygen atoms of the two maltol functions, able to lodge one hard metal ion such as sodium. On the other hand, L1 forms a dinuclear Cu(II)-species using the remaining unbound maltolic function which affords a Cu(II)-tetranuclear species in the solid state. This behavior is attributed to the different coordination requirements of the two metals, thus providing information for the choice of a suitable metal to preorganize side-arms on a polyamine macrocyclic scaffold. Potentiometric and UV-Vis solution studies as well as four crystal structures of metal-complexes support this conclusion.
11 citations