Direct theoretical a b i n i t i o calculations in exchange coupled copper (II) dimers: Influence of structural and chemical parameters in modeled copper dimers

Abstract

The influence of structural and chemical parameters on the singlet–triplet splitting (2J=ΔEST ) in modeled exchange coupled oxygen-bridged dimeric copper (II) complexes is studied, using an ab initio method followed by a perturbation development of the configuration interaction. The effect of varying the Cu–O–Cu′ angle and the Cu–O distance in the Cu2O2 core of modeled dimers is calculated. The results are comparable to the experimental ones. Changes in the geometric coordination around the copper (II) atom and around the oxygen atom of the core are studied. The results show that the magnitude of the exchange coupling strongly depends on both of these factors. Electronegativity effects are studied by varying the counterion in the model and by changing from alkoxo-bridged to hydroxo-bridged copper (II) dimers.

Absence of room temperature ferromagnetism in Fe stabilized ZrO2 nanostructures and effect of Fe doping on its structural, optical and luminescence properties

“…Similarly, if one Fe 3+ is doped (nearly comparable to experimental doping concentration 10 at. %) in the ZrO 2 structure, then one Zr 3+ will be formed for one oxygen vacancy to balance the charge or two Fe 3+ ions (higher doping concentration) will produce one oxygen vacancy in the ZrO 2 structure for charge compensation.The calculations have been done by employing breaking symmetry approach (BS)[30,31]. The BS approach to homo-binuclear and hetero-binuclear transition metal complexes provide good estimate of the exchange coupling mediated through different atomic centres in low spin open shell molecular systems.…”

Novel anion-tunable structural diversity and new topologies in CuII complexes of a Schiff base

“…Within the Cu 4 O 4 cubane unit, each Cu(O) 2 Cu bridging fragment with short CuÁ Á ÁCu distances in the ranges 2.903-2.907 Å for complex 2, exhibits bridging angles of approximately 94.9°and 97.8°, which connect equatorial positions on the neighboring square-pyramidal or octahedral Cu II atoms with Cu-O distances of $1.98 Å. According to the magneto-structural correlations for dialkoxido and dihydroxido-bridged dinuclear Cu II complexes [36][37][38][39]41], the above Cu-O-Cu bridging angles are predicted to transmit moderate to strong antiferromagnetic interactions, which agrees well with the experimental results. On the other hand, each Cu-O-Cu bridging fragment with long CuÁ Á ÁCu distances in the ranges 3.190-3.430 Å involves one equatorial position on the coordination sphere of a copper atom and one apical position on the coordination sphere of neighboring Cu II atom, where the density of the unpaired electron is very small (the unpaired electron is located in the d x 2 Ày 2 orbital, which lies in the basal plane and is directed toward the ligand atoms coordinated to the copper atom).…”

“…The antiferromagnetic (AF) interaction decreases with decreasing the h angle, showing a crossover point [below which the magnetic behavior changes from AF to ferromagnetic (F) coupling with J = 0] at about 97°. It was also shown that the position of the crossover point also depends on the s angle (out-of-plane displacement of the hydrogen or carbon atoms linked to the oxygen bridging atoms from the Cu 2 O 2 plane), so that the AF coupling decreases with increasing the s angle [38] Numerous examples of structurally and magnetically related bis(l-phenoxido)dicopper(II) complexes exist and, with the exception of a few cases, they all exhibit moderate to strong AF coupling [4]. DFT calculations carried out bis(l-phenoxido)dicopper(II) systems where the phenoxido bridge connects two equatorial positions on the Cu II atoms, clearly shows that the main structural factor controlling the magnetic exchange interactions is by far the value of the h angle.…”

Copper(II) complexes of open-chain thioether ligands terminated by salicylaldimine functionality*This article has a companion paper in this issue (doi: 10.1139/v11-081).

“…[3] and the average of the two Cu-OCu bridge angles (97.34°), an estimated value for 2J of -647.8 cm -1 is obtained, which is somewhat better agreement with the observed value of -585(10) cm -1 , suggesting that this is a more suitable model. Obviously, the model and particularly the nature of the bridge are important in development of satisfactory magnetostructural correlations and theoretical calculations 36 have suggested this should be the case.…”