Structure and Magnetic Properties of Tetrakis (3,4,5-trimethoxy-phenyl)porphinatomanganese (III) 2,3,5,6-Tetrafluoro-7,7,8,8-tetracyanoquinodimethenide: The First Example of an Isolated [TCNQF_4]~(·-)

摘要

The crystal structure of meso-tetrakis(3,4,5-trimethoxy-phenyl)porphinatomanganese(III) 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethenide, [MnT(MeO)_3PP][TCNQF_4]·3-(o-C_6H_4Cl_2), 1·3C_6H_4Cl_2, provides the first exampel of a nondimeric [TCNQF_4]~(·-) that is stabilized by trans-#mu#-coordination to Mn~III. Compound 1·3C_3H_4Cl_2 crystallizes in the monoclinic C2/c space group [a= 16.9486 (10)A, b = 25.7170(14) A, c = 19.4009(12)A, #beta# = 107.091(4) deg V = 8082.8(8) A~3, T = 200 K, Z = 4, R(F_O) = 0.0547]. The [TCNQF_4]~(·-）formulation was confirmed from the crystal structure data, as well as the v_CN absorption at 2196 and 2165 cm~(-1) in the IR spectrum. The [TCNQF_4]~(·-）moiety is planar with a methylene-carbon-ring-carbon distance of 1.41 A, which is 0.038A longer than that for TCNQF_4. 1·3C_6H_4Cl_2 forms 1-D zigzag chains of alternating 1~+ and [TCNQF_4]~(·-), where the Mn~III atoms are bound in a trans-#mu#-fashion with Mn-N and intrachain Mn ...Mn distances of 2.321(3) A and 12.685 (4) A, respectively. The MnNC angle and the dihedral angle between the [TCNQF_4]~(·-) and the mean MnN_4 planes are 135.9(2) deg and 46.4 deg, respectively, with the phenyl rings rotated 80 deg with respect to the mean porphyrin plane. The magnetic susceptibility of 1·2.3C_6H_4Cl_2 can be calculated from the Curie-Weiss expression with #theta# = -37 K (T > 250 K) and #theta#' = + 29 K) 975 < T < 200 K) with an observed minimum in #CHI#T(T), typical of ferrimagnets, at 215 (+-) 10 K. At 2 T the magnetization is 14.900 emuOe/mol or 89% of 16.755 emuOe/mol expected for an S_Tot = 2-1/2 = 2/3 system. The intrachain antiferromagnetic coupling, J/K_B, is-71K (-49cm~(-1); -61 meV) based on a fit to the Seiden expression for noninteracting chains comprsied of alternating quantum (S = 1/2) and classical (S > 1/2) spins, and the Hamiltonian H = -2JS_a ·S_b. Compound 1·2.3C_6H_4Cl_2 ferrimagnetically orders at 7.3 K [based on the maxima in the 10 Hz # CHI#'(T) data'. Hysteresis is observed at 2K with coercive field, H_cr, of 17.1 kOe and remnant magnetization of 7.200 emuOe/mol; hysteresisis not observed at 5K. This compound also displays metamagnetic behavior at 2K above a critical field of 20.2 kOe. The frequency-dependent transitions observed in the #CHI#'(T) and #CHI#''(T) a.c.data are attributed to the transition to a spin glass or superparamagnetic state.