Structure and Magnetic Properties of Antiferromagnetic Manganese(III) Tetrakis(4- methoxyphenyl)porphyrin Tetracyanoethenide, [MnTOMePP][TCNE].2PhMe, and Manganese(III) Tetrakis(2-fluorophenyl)porphyrin Tetracyanoethenide, [MnTFPP][TCNE].2PhMe.
The tetracyanoethylene (TCNE) electron-transfer salts of meso-tetrakis(4-methoxyphenyl)- and meso-tetrakis(2-fluorophenyl)porphinatomanganese(II), [MnTOMePP][TCNE].2PhMe, 1, and [MnTFPP][TCNE].2PhMe, 2, respectively, have been structurally and magnetically characterized. 1 and 2 belong to the triclinicP&onemacr; (No. 2) space group [1, a = 9.896(2) Å, b = 10.256(3) Å, c = 14.447(2) Å, alpha = 82.64(2) degrees, beta = 92.40(1) degrees, gamma = 109.07(2) degrees, T = -80 degrees C, Z = 1, and R(F(o)) = 0.0295; 2, a = 10.185(5) Å, b = 11.081(3) Å, c = 12.378(3) Å, alpha = 107.55(2) degrees, beta = 82.88(3) degrees, gamma = 111.09(3) degrees, T = -80 degrees C, Z = 1, and R(F(o)) = 0.0421]. 1 and 2 are coordination polymers with the Mn(III) sites bridged by trans-&mgr;-sigma-[TCNE](*)(-). The [TCNE](*)(-) is orientationally disordered in 2, with the minor form being rotated by 90 degrees with respect to the major form and in the same plane as the major form in an approximate 5:1 ratio. The Mn-N and intrachain Mn.Mn distances are 2.289 and 2.313 Å and 10.256 and 10.185 Å, and the Mn-N-C and the dihedral angle between the mean MnN(4)-porphyrin and the mean [TCNE](*)(-) planes are 165.53 and 78.1 degrees and 148.6 and 55.4 degrees for 1 and the occupancy-weighted average of 2, respectively. For 1 above 250 K the susceptibility can be fit by the Curie-Weiss expression with theta = -65 K, while between 75 and 190 K an effective theta of +21 K is observed; for 2 above 225 K, theta is -71 K, while between 40 and 100 K the effective theta is +45 K. The initial negative theta values along with minima in the chiT(T) data at 134 K (X = OMe) and 240 K (X = F) are consistent with antiferromagnetic coupling. One chi"(T) and two chi'(T) peaks are observed for both 1 and 2. The higher temperature [ approximately 10 K (1) and 12.5 K (2)] chi'(T) peaks are frequency independent, lack a corresponding chi"(T) absorption, and are assigned to a transition to an antiferromagnetic state. In contrast, the lower-temperature frequency dependent [5.6 K (1) and 7.5 K (2) at 10 Hz] chi'(T) peaks have a corresponding frequency dependent chi"(T) peaks and are assigned to the transition to a spin-glass or superparamagnetic state. The T(c)'s are defined as chi'(T) data taken at 10 Hz and are listed above.
Brandon
Erik J.
EJ
Department of Chemistry, University of Utah, Salt Lake City, Utah 84112-0850, and the Hauptman-Woodward Medical Research Institute, Buffalo, New York 14203.
Arif
Atta M.
AM
Burkhart
Brian M.
BM
Miller
Joel S.
JS