J. Limburg et al., High-frequency EPR study of a new mononuclear manganese(III) complex: [(terpy)Mn(N-3)(3)] (terpy=2,2 ': 6 ',2 ''-terpyridine), INORG CHEM, 40(7), 2001, pp. 1698-1703
The isolation and structural characterization of [(terpy)Mn-III(N-3)(3)], c
omplex 1, is reported (terpy = 2,2':6',2"- terpyridine). Complex 1, a produ
ct of the reaction between the mixed-valence dimer [(terpy)(H2O) Mn-III(O)(
2)- Mn-IV(OH2)(terpy)](NO3)(3) and NaN3, crystallizes in a triclinic system
, space group P (1) over bar, a = 8.480(1) Angstrom, b = 8.9007(2) Angstrom
, c = 12.109(2) Angstrom, alpha = 93.79(1)degrees, beta = 103.17(1)degrees,
gamma = 103.11(1)degrees and Z = 2. Complex 1 exhibits a Jahn-Teller disto
rtion of the octahedron characteristic of a six-coordinated high-spin Mn(II
I). A vibrational spectroscopic study was performed. The v(asym)(N-3) mode
of complex 1 appears in the IR as a strong band at 2035 cm(-1) with a less
intense feature at 2072 cm(-1), and in the FT-Raman as a strong band at 207
1 cm(-1) with a weaker broad band at 2046 cm(-1). The electronic properties
of complex 1 were investigated using a high-field and high frequency EPR s
tudy (190-475 GHz). The different spin Hamiltonian parameters have been det
ermined (D = -3.23 (+/-0.01) cm(-1), E = 0.48 (+/-0.01) cm(-1), E' = 0.53 (
+/-0.01) cm(-1), g(x) = 2.00 (+/-0.005), g(y) = 1.98 (+/-0.005); g(z) = 2.0
1 (+/-0.005)). These parameters are in agreement with the geometry of compl
ex 1 observed in the crystal structure, a D < 0 related to the elongated di
stortion, and a value of fin close to 0.2 as expected from the highly disto
rted octahedron. The two values of the E-parameter are explained by the pre
sence of two slightly different structural forms of complex 1 in the crysta
l lattice. A second hypothesis was explored to explain the experimental dat
a. The calculation for the simulation was done taking into account that the
g and D tensors are not collinear due to the low symmetry of complex 1. In
that case, the spin Hamiltonian parameters found are D = -3.29 (<plus/minu
s>0.01) cm(-1), E = 0.51 (+/-0.01) cm(-1), g(x) = 2.00 (+/-0.005), g(y) = 1
.98 (+/-0.005), and g(z) = 2.01 (+/-0.005).