Three novel tetranuclear copper(II) complexes namely [Cu4(L1)4]â2(dmf) (1), [Cu4(L1)4] (2) and [Cu4(L2)2(HL2)2(H2O)2]â2(ClO4)Â·6(H2O) (3) (H2L1, (E)â2-((1-hydroxybutan-2-ylimino)methyl)phenol; H2L2, (E)â2-((1-hydroxybutan-2-ylimino)methyl)â6-methoxyphenol)) were synthesized from the self-assembly of copper(II) perchlorate and the tridentate Schiff base ligands. The structural determination reveals that complex 1 crystallizes in the monoclinic system with space group C2/c, whereas both the complexes 2 and 3 crystallize in the triclinic system with space group P-1. Complexes 1 and 2 possess face-sharing dicubane core, on the other hand complex 3 has double open cubane core structure. The copper(II) ions in the cubane core are in distorted square planar geometries, and weak Ïâ¦Ï and CâHâ¦Ï interactions lead to formation of a 2D supramolecular architecture for complexes 1 and 2. At room temperature complexes 1, 2 and 3, exhibit fluorescence with a quantum yield (Î¦s) of 0.47, 0.49 and 0.38, respectively. Variable temperature magnetic susceptibility measurements in the range 2â300 K indicate an overall weak antiferromagnetic exchange coupling in all complexes. The PHI program was used to study their magnetic behaviour. In agreement with their face-sharing dicubane structure, a Hamiltonian of the type H =â J1(S1S2+S1S2â+S1'S2+S1'S2â) â J2S1S1â, where S1= S1â= S2= S2â= SCu=1/2, was used for studying complexes 1 and 2. Simulations performed suggest magnetic exchange constants with values close to J1=â20 cmâ1and J2=0 cm-1for these complexes. On the other hand, the spin Hamiltonian H =â J1(S1S4+S2S3) â J2(S1S3+S2S4) â J3S1S2, where S1= S2= S3= S4= SCu=1/2, was used to study the magnetic behaviour of the double open cubane core of complex 3 and a good agreement between the experimental and simulated results was found by using the parameters g1= g2=2.20, g3= g4=2.18, J1=â36 cm-1, J2=â44 cm-1and J3=0 cm-1.
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|Titolo:||Structural and magnetic characterization of three tetranuclear Cu(II) complexes with face-sharing-dicubane/double-open-cubane like core framework|
BERTOLASI, Valerio (Secondo)
|Data di pubblicazione:||2017|
|Appare nelle tipologie:||03.1 Articolo su rivista|