Abstract
The case of palladium(II) ions in molecular polyoxopalladates highlights the importance of accounting not only for nearest neighbour atoms or ions in order to understand, model or predict magnetic characteristics. Here, using site-specific soft X-ray magnetic circular dichroism (XMCD), the effects of different bond lengths, delocalization of 4d electrons, and 4d spin-orbit coupling on the electronic and magnetic properties are investigated and three different states identified: Conventional diamagnetism in a square-planar O4 coordination environment, paramagnetism caused by four additional out-of-plane oxygen anions, and an unusual diamagnetic state in the diamagnetic/paramagnetic crossover region modified by significant mixing of states and facilitated by the substantial 4d spin-orbit coupling. The two diamagnetic states can be distinguished by characteristic XMCD fine structures, thereby overcoming the common limitation of XMCD to ferro-/ferrimagnetic and paramagnetic materials in external magnetic fields. The qualitative interpretation of the results is corroborated by simulations based on charge transfer multiplet calculations and density functional theory results.
Highlights
The case of palladium(II) ions in molecular polyoxopalladates highlights the importance of accounting for nearest neighbour atoms or ions in order to understand, model or predict magnetic characteristics
The first example of this class, the polyanion [PdII13O2(OH)6(AsVO4)8]8−, denoted PdPd12As8 (4) in this work, was discovered in 20081. It is composed of a central palladium(II) ion surrounded by a distorted cubic shell of eight oxygen ions, which is in turn encapsulated in the cuboctahedral cavity of 12 palladium(II) ions in square-planar oxygen coordination environments ({Pd12}) and capped by eight arsenate (AsO43−) heterogroups
The discussion is divided into three parts: In the first part, we briefly discuss the oxygen contribution to the experimental X-ray magnetic circular dichroism (XMCD) spectra, before turning to the diamagnetism of palladium (II) ions in square-planar symmetry, i.e. the palladium(II) ions in the oxopalladate shell
Summary
The case of palladium(II) ions in molecular polyoxopalladates highlights the importance of accounting for nearest neighbour atoms or ions in order to understand, model or predict magnetic characteristics. The experimental XANES and XMCD data of PdPd12As8 were fitted by the same contribution of the 12 square-planar coordinated palladium(II) ions and an additional contribution of palladium(II) ions in a slightly modified crystal field, i.e. with reduced values of Dt and Ds (orange line in Fig. 6d) and a slightly increased d–d Coulomb repulsion.
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