Three new dinuclear bis-μ-azido-bridged Cu(II) compounds with di-2-pyridylamine as a ligand: Syntheses, X-ray structure and magnetic measurements

Competing Large and Small Angles in a Double End‐On Azido Copper(II) Binuclear Complex: A Combined Experimental and Theoretical Study of Magnetic Interactions

“…In the previously reported Cu II dimers with the double EO azido bridges, the [Cu 2 (N 3 ) 2 ] moieties are usually symmetric or quasisymmetric with two comparable bridging angles. [6][7] The asymmetry in 1 arises from the use of the asymmetric ligand, which does not allow inversion and mirror symmetry in the structure. The large steric hindrance introduced by the bulky ligand may also contribute to the large discrepancies in bridging angles and bond lengths.…”

“…(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) tion has been paid to binuclear azido-bridged Cu II systems, [6][7][8][9][10][11] which have a limited number of electrons (i.e., two unpaired electrons) involved in the interaction and provide the simplest model. Cu II ions usually adopt either a square planar, square pyramidal, or axially elongated octahedral geometries and are bridged by two azido ions in the µ-1,1 (end-on, EO) [6][7][8][9] or µ-1,3 (end-to-end, EE) [4a,4b,10,11] modes (Scheme 1).…”

“…Cu II ions usually adopt either a square planar, square pyramidal, or axially elongated octahedral geometries and are bridged by two azido ions in the µ-1,1 (end-on, EO) [6][7][8][9] or µ-1,3 (end-to-end, EE) [4a,4b,10,11] modes (Scheme 1). The bridge may adopt the "symmetric" equatorial-equatorial (eq-eq) fashion (i.e., occupy the equatorial positions of both Cu ions; Scheme 1c), with two comparable short Cu-N bonds (1.97-2.14 Å), [6,7,10] or the asymmetric equatorial-axial (eq-ax) fashion (i.e., occupy the equatorial position of one Cu ion but the axial position of the other metal ion; Scheme 1d) with short (1.97-2.08 Å, equatorial) and long (2.19-2.85 Å, axial) Cu-N bonds. [8,9,11] It is now accepted that the nature and magnitude of the magnetic exchange are not only dependent upon the bridging mode (EO or EE), but also strongly influenced by the arrangement (eq-eq or eq-ax) of the azido bridge between the metal ions.…”

“…[6,7,[12][13][14][15] Earlier studies seemed to suggest that the Scheme 1. The end-on (EO, a) and end-to-end (EE, b) coordination modes and the equatorial-equatorial (eq-eq, c) and equatorialaxial (eq-ax, d) disposition fashions of the azido bridge.…”

“…[15] The small-angle ferromagnetic regime was confirmed in a number of binuclear systems with double EO azido bridges (J ranging from 23 to 230 cm -1 ). [6,7] In contrast, the antiferromagnetic interaction for larger bridging angles has only been attributed in some mixed bridged systems, in which the metal ions are simultaneously linked by EO azido groups and bridges of other types. [13] To the best of our knowledge, synthetic species holding two large-angle eq-eq EO azido bridges have not been reported so far, nor have the species with simultaneous small-and large-angle bridges.…”