Structural Correlations in Jahn–Teller Systems of Mn³⁺ and Cu²⁺: Unraveling Local Structures through Spectroscopic Techniques

Abstract

An experimental correlation study between the low-symmetry 3d orbital splitting pattern, Δe and Δt, determined by optical spectroscopy, and the local distortion ρ, determined by X-ray diffraction, for different Cu2+ and Mn3+ fluorides and chlorides is presented. Single crystals of different dimensionalities were explored, some of them studied under high-pressure conditions. The collection of structural and spectroscopic data provides structural correlations relating ρ and Δe and Δt in Cu2+ and Mn3+ systems, showing that Δe (and Δt) scales with ρ. Such correlations can be used to estimate local distortions of Cu2+ (or Mn3+) introduced as impurities in different chloride and fluoride host lattices from spectroscopic data. The results can be interpreted in the framework of the Jahn–Teller theory and provide support for the proposed structural scenario. The influence of the crystal anisotropy in the local structure is analyzed as well and compared with transition metal ion systems having E⊗e Jahn–Teller (Cu2+, Mn3+) and singly orbital (Ni2+, Mn2+, Fe3+) ground states in octahedral symmetry.

Exploring Ultrafast Photoswitching Pathways in RbMnFe Prussian Blue Analogue

“…Mn(d x 2 Ày 2 )c haracter (Figure 4). Form any Mn III systems exhibiting Jahn-Teller distortion, [17] similar energy splitting were reported between occupied Mn(d z 2 )a nd unoccupied Mn(d x 2 Ày 2 )orbitals.Since ab initio calculations underestimate the gap,the Mn(d z 2 )!Mn(d x 2 Ày 2 )gap corresponds well to the Mn(d-d) band observed at 508 nm by ellipsometry [10e, 15] and in OD data (Figure S1). Thet ail of this band extends above 650 nm (1.9 eV).…”

Exploring Ultrafast Photoswitching Pathways in RbMnFe Prussian Blue Analogue

“…The optical transitions 81→89 and 82→90, calculated around 1.9 eV for α spins, have therefore a strong Mn( )→Mn( ) character (Figure 4). For many Mn III systems exhibiting Jahn–Teller distortion, [17] similar energy splitting were reported between occupied Mn( ) and unoccupied Mn( ) orbitals. Since ab initio calculations underestimate the gap, the Mn( )→Mn( ) gap corresponds well to the Mn(d‐d) band observed at 508 nm by ellipsometry [10e, 15] and in OD data (Figure S1).…”

Key Role of Deep Orbitals in the dx2–y2–d3z2–r2 Gap in Tetragonal Complexes and 10Dq

“…Experimentally, it has been found that 10 Dq depends on R – t , where the exponent t is often found to be close to 5 . By this reason, it is still claimed that the exponent t mainly comes from the CF contribution , despite this approach leading to 10 Dq values much smaller than experimental ones …”

“…Tetragonal CuF 6 4– units are also formed in Cu 2+ -doped K 2 ZnF 4 or Ba 2 ZnF 6 -layered perovskites though there is no Jahn–Teller effect as the a 1g (∼3 z 2 – r 2 ) and b 1g (∼ x 2 – y 2 ) levels are not degenerate following the tetragonal symmetry of the host lattice . Accordingly, the theory describing the Jahn–Teller effect , cannot, in general, be transferred ,, to understand pure layered compounds such as the orthorhombic K 2 CuF 4 or Cs 2 AgF 4 . , Nevertheless, the Jahn–Teller framework is still surprisingly applied − to d 9 ions under tetragonal or lower symmetries.…”