Spacer-armed copper(ii) complexes with benzenecarboxylic acids and trifluoroacetylacetone aroylhydrazones

Abstract

New bi- and trinuclear copper(ii) complexes of aroylhydrazones of TFA and benzenecarboxylic acids were synthesized and characterized. Despite long range intramolecular CuCu distances of about 10 Å, exchange couplings between paramagnetic centres are observed with J values of 0.33 and 0.37 cm(-1) in binuclear complexes, and -0.33 cm(-1) in trinuclear complexes. Seven hyperfine peaks with a value of aCu = 37.0 × 10(-4) cm(-1) are observed in EPR spectra of binuclear complexes. The possible mechanisms responsible for the observed weak long range coupling via aromatic spacers are discussed.

A computational study of structural and magnetic properties of bi- and trinuclear Cu(II) complexes with extremely long Cu---Cu distances

“…[19]. Checking the stability of the calculated high-spin (HS) and low-spin (BS) states indicates that all are internally stable.…”

“…These systems are interesting from a fundamental point of view since the nature of weak exchange interactions is a key topic of modern molecular spintronics [25]. Moreover, small values of J CuCu are responsible for the general form of the detected EPR spectrum; when the absolute value of exchange coupling constant J is comparable with the hyper-fine structure (HFS) constant for the copper atom (a Cu ≈ |J|) the EPR result could not be correctly assigned without spectral simulation, while in the cases a Cu >> |J| and a Cu << |J| the spectrum typically consist of four and seven lines, respectively, with the distinctive intensity ratio of 1:1:1:1 and 1:2:3:4:3:2:1 and hyperfine splitting of a and a/2, respectively [19]. kT kT…”

“…An alternative is the so-called "Brocken-Symmetry" (BS) approximation [32,33] that has been widely used for investigations of magnetic properties of numerous organometallic systems at the DFT level of theory [4-6, 14, 24]. In the present work we have particularly focused on the magnetic properties of two dinuclear and one trinuclear Cu(II) complexes with aroylhydrazones of trifluoroacetic and benzenecarboxylic acids (Figure 2) with extremely large space-separation of the paramagnetic centers (about 10 Å) [19]. Despite such a long Cu---Cu distance the studied complexes still demonstrate non-vanishing exchange coupling between space-separated unpaired electrons as has been detected by V. F. Shul'gin and coauthors by EPR spectroscopy and by ) (T  magnetic susceptibility measurements [19].…”

“…At the same time, a lot of dinuclear copper complexes with strongly space-separated (6-10 Å) copper(II) ions [19][20][21][22][23][24][25] possess a very weak ferro-/antiferomagnetic character due to the very weak exchange between the magnetic SOMOs. These systems are interesting from a fundamental point of view since the nature of weak exchange interactions is a key topic of modern molecular spintronics [25].…”

“…In the present work we have particularly focused on the magnetic properties of two dinuclear and one trinuclear Cu(II) complexes with aroylhydrazones of trifluoroacetic and benzenecarboxylic acids (Figure 2) with extremely large space-separation of the paramagnetic centers (about 10 Å) [19]. Despite such a long Cu---Cu distance the studied complexes still demonstrate non-vanishing exchange coupling between space-separated unpaired electrons as has been detected by V. F. Shul'gin and coauthors by EPR spectroscopy and by ) (T  magnetic susceptibility measurements [19]. Unfortunately, an unambiguous explanation of the magnetic exchange mechanism for the studied and related systems is rather difficult and remains an open task for computational inorganic chemistry.…”