X- and Q-Band EPR Studies of the Dinuclear Mn(II) Complex [(Bpmp)Mn2(-OAc)2]+. Determination of the Spin Parameters for the S = 1 and S = 2 Spin States

A new (mu)-phenoxo-bis-(mu)-acetato di-Mn(II) complex using the BpmpH ligand was isolated as a perchlorate salt (BpmpH = 2,6-bis[bis (2-pyridylmethyl)aminomethyl]-4-methyl-phenol). The X-ray structure has been solved showing that the two Mn(II) ions are in a distorted octahedral environment. Investigation of the variation of the molar magnetic susceptibility upon temperature reveals an antiferromagnetic exchange interaction between the two high-spin Mn(II) ions. Fitting of the experimental data led to g = 1.99 and J = 9.6 cm^-1 (HHDvV = JSA.SB). EPR spectra recorded on a powder sample of [(Bpmp)Mn2((mu)-OAc)2](ClO4).0.5H2O at X-band between 4.3 K and room temperature and at Q-band between 5 and 298 K are presented. A new method based on a scrupulous examination of the variation upon temperature of these experimental spectra is developed here to first assign the transitions to the relevant spin states and second to determine the associated spin parameters. This approach is compared to the deconvolution process that has been previously applied to dinuclear Mn(II) complexes or metalloenzyme active sites. Crystallographic data is as follows: triclinic, space group P1, a = 10.154(2) (angstrom), b = 12.0454(2) (angstrom), c = 17.743(4) (angstrom), (alpha)= 101.69(3) °, (beta)= 93.62(3) °, (gamma)= 94.67(3) °, Z = 2.