Powder electron paromagnetic resonance studies of some pentamminechromium(III) complexes

Abstract

Electron paramagnetic resonance spectra of magnetically dilute powder samples have been used to study bonding effects in [Cr(NH3)5HjO]3+, [Cr(NH3)sCl]I+, and [Cr(NH3)sBr]2+. The influence of the lattice has been shown to be negligible for the former two complexes which demonstrates the intramolecular origin of the spin-Hamiltonian parameters. Bonding of the equatorial ammine ligands was shown to be invariant to the axial ligand changes. The zero-field splitting parameters, appear to be sensitive to -bonding effects with significant bonding being indicated for the water ligand in the aquo complex.

A New Geometry for Homoleptic Organochromium Compounds

“…9−10 GHz in X-band). The EPR spectrum of 1 bears remarkable similarities with those reported for six-coordinate Werner-type Cr III compounds such as [Cr III Cl 5 (OH 2 )] 2- , trans -[Cr III (ox) 4 XX‘] n - , trans -[Cr III (NH 3 ) 4 XX‘] n + , , trans -[Cr III (py) 4 XX‘] n + , trans -[Cr III (en) 2 X 2 ] n + , or trans -[Cr III (cyclam)X 2 ] n + , in which the Cr III center is located in different tetragonal environments (ox = oxalato; cyclam = 1,4,8,11-tetraazacyclotetradecane; X, X‘ = neutral or singly charged monodentate ligands). In all these cases an isotropic Zeeman contribution was assumed and the spin Hamiltonian used is given, in the principal axes of the zero-field contribution, by with S = 3/2 and where g represents the gyromagnetic factor, μ B is the Bohr magneton, and D and E describe the zero-field contribution in the standard form.…”

“…In this context, it is worthwhile noting that EPR spectroscopy is a very sensitive tool, especially for S > 1/2 systems, providing in some instances information on local distortions that are imperceptible to other structural techniques including X-ray diffraction methods. Lattice effects are known to affect variations of the zero-field splitting tensor in the aforementioned [Cr III (NH 3 ) 5 X] 2+ complexes, while they exert little effect on the g̃ -tensor 26b. The central features of the W-band EPR spectrum of 1 (see inset in Figure ), corresponding to the |+1/2〉 ↔ |−1/2〉 transitions along the principal axis, further suggest the existence of two Cr III entities.…”

Bifunctional Materials Based on the Photochromic Cation [RuNO(NH3)5]3+ with Paramagnetic Metal Complex Anions

“…It is important to note that the 2D splitting is sensitive to the strength of π-type metal-ligand interactions, which are especially strong for CN -ligands. [33] Qualitative estimates of the 2D value (in terms of angular-overlap model calculations taking into account spin-orbit interaction, see ref. [34] for detail) indicate that for some hypothetical distortions of [Cr(CN) 6 ] 3-complexes corresponding to the ''frozen'' crystal structure of 1 (Figure 2), the zero field splitting can reach a value of 3 cm -1 or even more.…”

Magnetic and Optical Studies on an S = 6 Ground-State Cluster [Cr12O9(OH)3(O2CCMe3)15]: Determination of, and the Relationship Between, Single-Ion and Cluster Spin Hamiltonian Parameters

“…2 Moreover, the observation of magnetization quantum tunneling effects 3 has led to the proposal that SMMs could be exploited as Qbits in quantum computing. 4 The original discovery was in a dodecametallic, mixedvalence manganese cluster [Mn 12 O 12 (O 2 CMe) 16 (H 2 O) 4 ], trivially known as "Mn 12 ", which has an S ) 10 ground state with an axial ZFS of -0.42 K. 1 Because the temperature below which SMMs operate is controlled in large part by the product |D S |S 2 , where D S is negatiVe in sign, a primary goal in this field is to maximize S and |D S |. This requires a detailed understanding of the factors that control these parameters.…”