Magnetic Exchange Interactions in Binuclear Transition-metal Complexes of a Binucleating Clathrochelate Ligand


A series of homo- and heterobinucleating transition-metal complexes of the form [LM a IIM b II]BF 4 has been synthesized, where L 3- is the deprotonated form of a new clathrochelating ligand resulting from the Schiff-base condensation of 3 mol of 2-hydroxy-5-methylisophthalaldehyde and 2 mol of tren [tris(aminoethyl)amine]. Complexes have been prepared with the following divalent metal ions: Cu 2, Fe 2, Co 2, Mn 2, CoFe, MnFe. The binucleating nature of the ligand was established by the single-crystal X-ray structure of [LCoFe]BF 4, which crystallizes in the monoclinic space group Cc with a = 20.501 (10) Å, b = 11.833 (3) Å, c = 17.889 (9) Å, β = 112.44 (4)°, and Z = 4. The structure was refined by full-matrix least-squares methods to final residual values of R = 0.083 and R w = 0.082. The cation contains both metal ions in highly distorted, six-coordinate ligand environments. The metal ions, separated by 3.07 Å, are bridged by the three deprotonated phenolic oxygens; three tren imine nitrogens complete the coordination environment. Variable-temperature (4.2-285 K) magnetic susceptibility measurements on the series of homobinuclear complexes show that the high-spin metal centers are weakly antiferromagnetically coupled. The susceptibility data for each complex were least-squares fit to the equations resultant from the spin Hamiltonian for an isotropic exchange interaction (Ĥ = -2JŜ 1·Ŝ 2) to give exchange parameters (J) of -33 cm -1 (Cu 2), -0.93 cm -1 (Co 2), -0.82 cm -1 (Fe 2), and -2.8 cm -1 (Mn 2). The iron-57 Mössbauer data for [LFeMn]BF 4 and [LFe 2]BF 4 are consistent with high-spin ferrous ions, although the temperature-dependent spectra (300-5.4 K) of the latter complex are unusual and suggest the presence of two inequivalent iron coordination environments. © 1985 American Chemical Society.



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© 1985 American Chemical Society (ACS), All rights reserved.