Spectrochemical series

About: Spectrochemical series is a research topic. Over the lifetime, 417 publications have been published within this topic receiving 11020 citations.

Photophysical effects of metal-carbon .sigma. bonds in ortho-metalated complexes of iridium(III) and rhodium(III)

Abstract: Dichloro-bridged dimers of the type (M(L)/sub 2/Cl)/sub 2/, where L is 2-phenylpyridine (ppy) or benzo(h)quinoline (bzq) and M is Rh(III) or Ir(III), have been characterized by /sup 13/C and /sup 1/H NMR spectroscopies and by absorption and emission spectroscopies. The NMR results confirm previous formulations of the complexes as dichloro-bridged ortho-metalated dimers in halocarbon solvents but indicate that they are cleaved to monomeric species of the type M(L)/sub 2/CIS in ligating solvents such as dimethylformamide (S = solvent). The absorption spectra of each of the complexes contain several low-energy bands which are assigned as metal-to-ligand charge-transfer (MLCT) transitions. All four of the dimers emit light following photoexcitation of their glassy solutions at 77 K. Their emission spectra and lifetimes lead to assignments of their emitting states as intraligand for the Rh(III) dimers and MLCT for the Ir(III) dimers. The Ir(III) dimers are also found to emit light following excitation at 295 K in deaerated dichloromethane. No emission is seen from the Rh(III) dimers under these conditions. Comparison of these results with previous results from studies of similar Rh(III) and Ir(III) complexes of 2,2'-bipyridine (bpy) and 1,10-phenanthroline (phen) indicates that the ortho-metalated ligands are considerably higher than bpy and phen inmore » the spectrochemical series. In addition to raising the energy of ligand field excited states in their complexes, relative to similar bpy and phen species, they induce lower energy charge-transfer transitions. These effects are consistent with the synergistic function of the ortho-metalated ligands as both strong sigma donors and ..pi.. acceptors.« less

Electronic Structure, Spectra, and Magnetic Properties of Oxycations. III. Ligation Effects on the Infrared Spectrum of the Uranyl Ion

Abstract: A series of uranyl complexes KxUO2Ly(NO3)2, where L is the variable ligand (or ligands), has been prepared; it has been shown that a ligand series may be defined using the antisymmetric stretching frequency of the uranyl entity, and this series exhibits a remarkable parallelism with the spectrochemical series defined by Δ in octahedral complexes of transition metals of the 1st and 2nd series. This parallelism has been rationalized using a mixed ligand field theory in which the uranyl ion is considered subject to bonding with ligands which are arranged hexagonally in a plane equatorial to the O–U–O axis. It is shown that the large changes of ν3 and ν1 are due primarily to electron population of the φu and δu atomic orbitals of uranium. Such population is physically equivalent to the reductions AmO2+ +→AmO2+ and NpO2+ +→NpO2+, which cause a decrease of approximately 100 cm—1 in ν3. It is further shown that Δν3 = — electrostatic effect — σ(L→M) — π(L→M) ± π(M→L), where in the last term the plus sign is the ...

Slow magnetic relaxation in a family of trigonal pyramidal iron(II) pyrrolide complexes.

Abstract: We present a family of trigonal pyramidal iron(II) complexes supported by tris(pyrrolyl-α-methyl)amine ligands of the general formula [M(solv)(n)][(tpa(R))Fe] (M = Na, R = tert-butyl (1), phenyl (4); M = K, R = mesityl (2), 2,4,6-triisopropylphenyl (3), 2,6-difluorophenyl (5)) and their characterization by X-ray crystallography, Mossbauer spectroscopy, and high-field EPR spectroscopy. Expanding on the discovery of slow magnetic relaxation in the recently reported mesityl derivative 2, this homologous series of high-spin iron(II) complexes enables an initial probe of how the ligand field influences the static and dynamic magnetic behavior. Magnetization experiments reveal large, uniaxial zero-field splitting parameters of D = -48, -44, -30, -26, and -6.2 cm(-1) for 1-5, respectively, demonstrating that the strength of axial magnetic anisotropy scales with increasing ligand field strength at the iron(II) center. In the case of 2,6-difluorophenyl substituted 5, high-field EPR experiments provide an independent determination of the zero-field splitting parameter (D = -4.397(9) cm(-1)) that is in reasonable agreement with that obtained from fits to magnetization data. Ac magnetic susceptibility measurements indicate field-dependent, thermally activated spin reversal barriers in complexes 1, 2, and 4 of U(eff) = 65, 42, and 25 cm(-1), respectively, with the barrier of 1 constituting the highest relaxation barrier yet observed for a mononuclear transition metal complex. In addition, in the case of 1, the large range of temperatures in which slow relaxation is observed has enabled us to fit the entire Arrhenius curve simultaneously to three distinct relaxation processes. Finally, zero-field Mossbauer spectra collected for 1 and 4 also reveal the presence of slow magnetic relaxation, with two independent relaxation barriers in 4 corresponding to the barrier obtained from ac susceptibility data and to the 3D energy gap between the M(S) = ±2 and ±1 levels, respectively.