Copper coordination chemistry of novel octadentate, tetranucleating, bis(diazine) ligands. Structural and magnetic properties of tetranuclear complexes involving a rectangular array of copper(II) centers

Magnetostructural Correlations in Bis(μ2-phenoxide)-Bridged Macrocyclic Dinuclear Copper(II) Complexes. Influence of Electron-Withdrawing Substituents on Exchange Coupling

“…Bis(1,3,5-triketonato)dicopper(II) complexes are known to be very strongly antiferromagnetically coupled, and for a series of 1,5-(R,R‘)-disubstituted derivatives (R = R‘ = CH 3 ; R = CH 3 , R‘ = Ph; R = R‘ = CF 3 ), with Cu−O ketonate −Cu angles in the range 103−103.5°, −2 J falls in the range 625−740 cm -1 . − These levels of antiferromagnetic exchange are somewhat smaller than observed for the phenoxide-bridged macrocyclic complexes under discussion (−2 J calc = 830 cm -1 for Cu−O−Cu = 103°), but the highly delocalized nature of the triketonate groups cannot be ignored in assessing the mechanism for exchange in such complexes. Although this would involve a long exchange distance (a minimal separation of six bonds for both types of complex; <8 Å), it is not unreasonable, given the reports of significant antiferromagnetic exchange between square pyramidal copper(II) centers separated by conjugated, aromatic ligands with six bonds (7.6 Å; −2 J = 21−26 cm -1 ), eight bonds (≈11.8 Å; − J = 36−210 cm -1 ), and nine bonds (11.25 Å; −2 J = 140 cm -1 ) . Significant antiferromagnetic coupling was also observed between distant ruthenium(III) ions (11 bonds), but involving a dπ−pπ mechanism.…”

Tetranuclear Copper(II) and Nickel(II) Cluster Complexes Derived by Self-Assembly from a Series of Tetradentate Diazine Ligands: Structural and Magnetic Studies

“…A significant amount of control can be exerted over the formation of relatively low nuclearity molecular clusters (<M 6 ) by the use of polyfunctional and polytopic ligands with well defined and appropriately positioned coordination pockets. Cu 4 , Cu 6 , and Cu 8 complexes have been synthesized by the use of poly-phthalazine ligands with fused and polypodal ligand fragments. , Transition metal template cyclizations have successfully produced many tetranuclear Mn 4 , , Ni 4 , − Cu 4 , − and Zn 4 13,14 complexes, in which the metal ions are bridged exclusively by oxygen donor groups. The size of the macrocyclic ring can be modified by adjustments of chelate ring sizes, and with smaller chelate rings macrocyclic ligands accommodating six metals (Cu 6 , Ni 6 ) can be produced, , and in the copper case association between the rings produces spin coupled, dodecanuclear systems.…”