Three new dinuclear copper(ii) complexes with [Cu(μ_1,3-N₃)₂Cu]²⁺and [Cu(μ_1,1-N₃)₂Cu]²⁺asymmetrical cores: syntheses, structures and magnetic behaviour

Ferromagnetic Interaction in an Asymmetric End‐to‐End Azido Double‐Bridged Copper(II) Dinuclear Complex: A Combined Structure, Magnetic, Polarized Neutron Diffraction and Theoretical Study

“…In early studies, the EO coordination mode was systematically found to be symmetric and to exhibit ferromagnetic Cu À Cu interactions. In contrast, for the EE systems (Table 1) the interactions were found to be zero [19] or weakly antiferromagnetic [11,17,21] (J < À100 cm…”

“…In these systems, the azido groups bridge the copper(II) ions either through one terminal nitrogen atom (m-1,1), in a socalled end-on coordination mode (abbreviated hereafter EO), [3][4][5][6][7][8][9][10][11][12][13][14][15][16] or through two terminal nitrogen atoms (m-1,3) in an end-to-end coordination mode (EE) as shown in Scheme 1. [11,[17][18][19][20][21][22][23] For both EO and EE systems, the bridge may be either symmetric (Scheme 1 a), when the two N À Cu bonds are Abstract: A new end-to-end azido double-bridged copper(II) complex [Cu 2 L 2 (N 3 ) 2 ] (1) was synthesized and characterized (L = 1,1,1-trifluoro-7-(dimethylamino)-4-methyl-5-aza-3-hepten-2-onato). Despite the rather long Cu À Cu distance (5.105(1) ), the magnetic interaction is ferromagnetic with J = + 16 cm À1 (H = ÀJS 1 S 2 ), a value that has been confirmed by DFT and highlevel correlated ab initio calculations.…”

“…Most EO systems are symmetric, [3-5, 7-10, 24] whereas EE systems are generally asymmetric. [11,17,19,[21][22][23] From the magnetic point of view, a key distinction has long prevailed between the EO and EE coordination modes. In early studies, the EO coordination mode was systematically found to be symmetric and to exhibit ferromagnetic Cu À Cu interactions.…”

“…[20,25] In the last five years, this picture has changed somewhat because more azido-bridged copper(II) dinuclear complexes have been reported. Some asymmetric EO systems [11][12][13] have now been found that exhibit antiferromagnetic Cu À Cu interactions, while several cases of ferromagnetic couplings have been reported for asymmetric EE systems. [11,22,23] In the early studies, [3][4][5][6][17][18][19][20] the symmetric EO coordination mode behavior seemed intrinsically ferromagnetic and independent of any structural parameters.…”

“…Some asymmetric EO systems [11][12][13] have now been found that exhibit antiferromagnetic Cu À Cu interactions, while several cases of ferromagnetic couplings have been reported for asymmetric EE systems. [11,22,23] In the early studies, [3][4][5][6][17][18][19][20] the symmetric EO coordination mode behavior seemed intrinsically ferromagnetic and independent of any structural parameters. This is why most previous theoretical studies focused on EO systems to explain such peculiar behavior, [24,[26][27][28][29][30] which was initially attributed to spin polarization effects.…”