Exchange coupling in tris(.mu.-hydroxo)bis[(1,4,7-trimethyl-1,4,7-triazacyclononane)chromium(III)] triperchlorate trihydrate

Abstract

Exchange Coupling in Tris(p-hydroxo) bis[ (1,4,7-trimethyl-1,4,7-triazacyclononane)chromium( 111)] Triper c hlora t e T r i hydra t eMagnetic susceptibility data have been collected in the temperature range 1.7-336 K for the tris(r-hydroxo)-bridged bimetallic chromium complex [LCr(OH)3CrL](C104)3.3Hz0. The magnetic susceptibility data reflect antiferromagnetic exchange coupling interactions and may be fit with the assumption of bilinear and biquadratic exchange of the form -WS1.S2j(S1.S2)* with the Van Vleck equation. The best fit of the experimental data yields J = -64 (1) cm-I, j = 1.8 (2) cm-I, and g = 1.98 ( 1 ) with an estimated impurity percentage of 0.84 (1). The large value of the bilinear exchange coupling constant reflects the number of bridging hydroxo groups as well as structural features of the superexchange pathway. EPR spectra collected as a function of temperature at X-and Q-band have been theoretically simulated with the spin Hamiltonian parameters D = f0.34 cm-I, 0, = *0.18 cm-I, and g = 1.98, with AHpp = 150 G .A flow type cryostat with an internal helium reservoir was used for the measurements between 336 and 1.7 K. The temperature was measured with a calibrated Au (0.3% Fe)/chromel thermocouple, and Veal, J. T.; Jeter, D. Y.; Hempel, J. C.; Eckberg, R. P.; Hatfield, W. E.: Hodson. D. J. Inorp. Chem. 1973. 12. 2928. Engel, Py; Gidel, H. U."Inorg. Chem. 1977, 16, 1589. Urishiyama, A.; Nomura, T.; Nakahara, M. Bull. Chem. SOC. Jpn. 1970, 43, 3971. Yevitz, M.; Stanko, J. A. J. Am. Chem. SOC. 1971, 93, 1512.

Broken symmetry approach to density functional calculation of zero field splittings including anisotropic exchange interactions

“…49 The coupling of the two chromium spins with s 1 = s 2 = 3 2 results in four low-lying spin states with S = 0, 1, 2, 3. There is antiferromagnetic coupling of the two chromium centers, the fit of the magnetic data was performed with explicit consideration of biquadratic exchange, and for J 12 a value of 128 cm −1 has been obtained.…”

Exchange interactions in a trigonal chromium(III) pair

“…The Cr(III)-Cr(III) separation, 2"664(1)~1 [9], is the shortest known in a Cr(III) complex. Accordingly the exchange coupling is strong, as shown by magnetic susceptibility measurements [10] and, more accurately, a preliminary spectroscopic study [11]. The strong exchange interactions lead to distinct features in the spectrum as was illustrated in [11].…”

“…For convenience, however, we shall continue to designate the lower energy combinations as (2E 4A2) and the higher energy ones as (2 T1 ~ • 4A2 ) pair states. (10). (c) eigenvalues of the "*A24A2 and 4Txao4A 2 pair states.…”

Multireference Approaches to Spin‐State Energetics of Transition Metal Complexes Utilizing the Density Matrix Renormalization Group

“…Another example of such application is provided in the case of the triply hydroxo‐bridged chromium dimer 13 , [L 2 Cr(III) 2 (μ‐OH) 3 ] +3 (L = N,N′,N″ ‐trimethyl‐1,4,7‐triazacyclononane) . The two Cr(III) ions are antiferromagnetically coupled (experimental J = −66 cm −1 ) to yield a diamagnetic ( S = 0) ground state.…”