ABSTRACT
The first example of a triple formato/hydroxido/sulfato (FHS) bridge for any metal is reported in compound [Cu2(bpym)(OH)(HCO2)(SO4)(H2O)2]·3H2O (1). Its structure shows the presence of alternating triple FHS bridges and 2,2'-bipyrimidine (bpym) ones. Although in the initial synthesis the sulfate anions were introduced accidentally, here we report the rational synthesis and the magnetic properties of this compound. The magnetic properties show that 1 is an alternating ferro/antiferromagnetic (F/AF) chain compound with predominant antiferromagnetic interactions and were fit to an alternating F/AF S = (1)/2 chain with g = 2.103, JAF = -139 cm(-1), and JF = 116 cm(-1) (α = JF/|JAF| = 0.83). The JAF value found corresponds very well to those previously reported for Cu-bpym-Cu bridges (average value of ca. -150 cm(-1)). The JF value is also very close to the estimated one (ca. 100 cm(-1)) from magneto-structural correlations in triply Cu-Cu bridged compounds with both hydroxido and carboxylato bridges in equatorial positions.
ABSTRACT
Herein, we present two geometrical models based on an effective point-charge approach to provide a full description of the lowest sublevels in lanthanoid single ion magnets (SIMs). The first one, named as the Radial Effective Charge (REC) model, evaluates the crystal field effect of spherical ligands, e.g. F(-), Cl(-) or Br(-), by placing the effective charge along the Ln-ligand axes. In this case the REC parameters are obtained fitting high-resolution spectroscopic data for lanthanoid halides. The second model, named as the Lone Pair Effective Charge (LPEC) model, has been developed in order to provide a realistic description of systems in which the lone pairs are not pointing directly towards the magnetic ion. A relevant example of this kind is provided by the bis(phthalocyaninato)lanthanoids [Ln(Pc)(2)](-). We show that a fit of the magnetic properties of the [Ln(Pc)(2)](-) (Ln = Tb, Dy, Ho, Er, Tm and Yb) allows us to extract the LPEC parameters for the lanthanoid complexes coordinated to sp(2)-nitrogens. Finally, we show that these effective corrections may be extrapolated to a large variety of lanthanoid and actinoid compounds, having either extended or molecular structures.
ABSTRACT
The microscopic theory of the magnetically anisotropic effective pseudo-spin-(1)/(2) Hamiltonian for a pair of Co(2+) ions is reported. In the framework of the second-order perturbation approach, the analytical expressions are found for the components of the tensor of the exchange interaction, g-tensor, and the factor in the temperature independent paramagnetic contribution. The parameters of the Hamiltonian are expressed in terms of the basic intra- and intercenter parameters of the pair, namely, the spin-orbit coupling constant, orbital reduction factor, exchange integral, and low symmetry crystal field parameters including axial and rhombic terms.
