EPR of chromium(3+) in tris(acetylacetonato)gallium(III) single crystals

Abstract

EPR of Cr3+ in gallium acetylacetonate was studied at X-band. Two crystallographically inequivalent centers were observed. Their spin-Hamiltonian parameters (g = 1.997 (3); |6°| = 0.593 (3) and 0.599 (3) cm™1, respectively; |¿>|| = 0.03 (7) and 0.09 (7) cm™1, respectively) differ very little from each other and from those for the isomorphous aluminum and cobalt(III) compounds. No changes were observed between 298 and 20 K. Thus, the geometry of the paramagnetic ion in such molecular crystals seems to be little affected by changes in the size of the host ion and temperature. The zero-field-splitting (ZFS) pattern can be satisfactorily reproduced by the superposition model with an intrinsic ZFS parameter |62| of 5.0 cm™1. This pattern thus seems to be largely caused by the distortion of the first coordination sphere of oxygens. The cause of occurrence of two crystallographically inequivalent

Near-infrared 2Eg → 4A2g and visible LMCT luminescence from a molecular bis-(tris(carbene)borate) manganese(IV) complex

“…25 Spectra plotted to match intensity of the highest band are given in Fig. S1 [32][33][34][35] and Mn(IV). 31,[36][37][38][39] This result indicates that there is nothing unusual about the spin quartet ground state of the title complex.…”

[CrIII8MII6]12+ Coordination Cubes (MII=Cu, Co)

“…The nature of the weak exchange interactions in 1 and 2 was further probed by Q-and W-band EPR spectroscopy (34 and 94 GHz, respectively). Spectra of [Cr III L 3 ], that is, the isolated corner fragment of 1 and 2 at 5 K are those of an S Cr = 3/2 (g Cr = 1.97) with near axial ZFS parameters of D Cr = À0.55 and E Cr = 0.025 cm À1 , in the range found for other [Cr(diketonate) 3 ] complexes [17] (Figures S5 and S3; simulated [22] with a Gaussian linewidth of 60 mT and a 10 % D-strain).…”

“…In both limiting models, we neglected the single-ion anisotropy of Cr III , D Cr , as this is usually of the order of 1 cm À1 . [17] Given that D Cu = 0, we only applied the isotropic model for the analysis of 1. We started with the isotropic model for both 1 and 2.…”

Hybrid Organic–Inorganic Rotaxanes, Including a Hetero‐Hybrid [3]Rotaxane Featuring Two Distinct Heterometallic Rings and a Molecular Shuttle

“…Spectra of the [2]rotaxane 6 are those of an isolated high spin Fe III ion (S = 5/2) with axial (j D j)and rhombic (E)zero-field splitting parameters of 0.17 and 0.045 cm À1 ,r espectively.T here are some minor spectral changes in the [3]rotaxane 1 that can be modelled as small changes in E. Similarly,spectra of 3 can be modelled as asingle S = 3/2 (D = À0.53, E = 0.03 cm À1 )owing to Cr III .T he larger j D M j and smaller rhombicity (E/D)f or M = Fe compared to Cr in {Ti 7 M}, and also the magnitudes of D and E,a re typical for monometallic {MO 6 }c omplexes,f or example,[ M(diketonates) 3 ]. [18,19] The D Cr value in {Ti 7 Cr} is significantly larger than that in the parent {Cr 7 M} family: [20] this must be af unction of the {Cr(O carboxylate ) 4 (O) 2 }v ersus {Cr(O carboxylate ) 4 (F) 2 }c rystal fields.T he implication is that oxide is acting as ab etter p-donor, resulting in aw eaker crystal field and hence larger ZFS via mixing with excited states,and that this is more important than the greater charge.…”