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.