Asymmetric Azido−Copper(II) Bridges:  Ferro- or Antiferromagnetic? Experimental and Theoretical Magneto−Structural Studies

Abstract

Reaction of NaN(3) with the [Cu(II)(tn)](2+) ion (tn = 1,3-diaminopropane) in basic aqueous solution yields the azido-bridged complex of formula [Cu(2)(tn)(2)(N(3))(4)] (1), which is characterized by X-ray crystallography. The structure of 1 is made up of dinuclear neutral complexes, of formula [Cu(2)(tn)(2)(N(3))(4)], resulting from the assembling of two mononuclear units through two equivalent end-on azide bridges connecting asymmetrically two Cu(tn)(N(3))(2) entities. These dinuclear units are connected through two asymmetric end-to-end N(3) bridges to form a chain of dimers. Magnetic measurements for compound 1 show weak antiferromagnetic exchange interactions between the Cu(II) ions. The magnetic data were modeled using the susceptibility expression derived for an alternating AF S = 1/2 chain. A very satisfactory fit over the whole temperature range was obtained with g = 2.1438(4), J(1) = -3.71(2) cm(-1), and J(2) = -3.10(2) cm(-1) (J(1) and J(2) are the singlet-triplet separations). This magnetic behavior differs from those observed for similar examples which were reported as having alternating ferro- and antiferromagnetic exchange interactions; thus, DFT calculations were done to understand the nature of the magnetic coupling in such asymmetric end-on and end-to-end N(3) bridges. Theoretical results show that the double asymmetric end-on bridges produce antiferromagnetic coupling while the end-to-end ones can present ferro- or antiferromagnetic coupling depending on the copper coordination sphere.

A polynuclear and two dinuclear copper(II) Schiff base complexes: Synthesis, characterization, self-assembly, magnetic property and DFT study

“…It explains the weak antiferromagnetic exchange observed in 1. Similar conclusion has also been drawn by other groups [31].…”

“…On the other hand, due to the absence of any meaningful overlap between magnetic orbitals, basalapical bridges usually give rise to very small magnetic couplings for end on modes [24][25][26][27][28][29][30][31]. Same is the case for the end to end dca bridged complexes due to relatively longer distance between the copper(II) centres [32][33].…”

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

“…[60,61] Broken Symmetry (BS) DFT calculations have turned out to reach agreement with experiments for dinuclear copper(II) systems as well as for several families of compounds. [13,27,34] J is directly accessible using Noodlemanns expression [Eq. (5)]:…”

“…[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.…”

Structural and Magnetic Properties of MnIII and CuII Tetranuclear Azido Polyoxometalate Complexes: Multifrequency High‐Field EPR Spectroscopy of Cu4 Clusters with S=1 and S=2 Ground States

“…Very recently, magnetostructural correlations for such asymmetrically bridged compounds based on DFT calculations have been proposed. [14] Nevertheless, synthesis and physical characterization of new azido-bridged coordination complexes are still of interest to define the structural factors governing the exchange coupling between azido-bridged paramagnetic centers, since magnetostructural correlations have only been proposed for a few systems such as basal-basal end-on Cu II[15] and Mn II[16] compounds. Interestingly, we have shown that the synthesis of POM/N 3 À complexes leads to azido compounds characterized by original structural features that differ from those obtained using organic ligands.…”