Structure and Magnetism of Dinuclear Copper(II) Metallacyclophanes with Oligoacenebis(oxamate) Bridging Ligands:  Theoretical Predictions on Wirelike Magnetic Coupling

Self-assembly of the ligands N,N'-1,5-naphthalenebis(oxamate) (1,5-naba) and N,N'-2,6'-anthracenebis(oxamate) (2,6-anba) by Cu(II) ions affords the two new dicopper(II) metallacyclophanes 2a and 3b, whereby the metal centers are connected by double naphthalene- and anthracenediamidate bridges with alpha,alpha' and beta,beta' substitution patterns, respectively. Despite the largely different intermetallic distances of 8.3 A (2a) and 12.3 A (3b), magnetic susceptibility measurements show a moderately strong antiferromagnetic coupling with rather similar J values in the range from -20.5 to -20.7 (2a) and from -21.2 to -23.0 (3b) cm(-1) (H = -J S1 x S2; S1 = S2 = 1/2). Density functional theory calculations on the two series of dicopper(II) metallacyclophanes 1a-10a and 1b-10b with linear alpha,alpha'- and beta,beta'-disubstituted oligoacenediamidate bridges, respectively, confirm the better efficiency of the latter substitution pattern on long-range magnetic coupling. More importantly, they predict a unprecedented wirelike magnetic behavior for the longest members of the series with octacene through decacene spacers (J values up to +3.0 cm(-1) for intermetallic distances reaching 28.8 A).