Effect of thermal annealing on the ferrimagnetic behavior and ordering of the [MnTXPP]+[TCNE]˙−·solv (X = F, Cl, Br, I; solv = PhMe, CH2Cl2) family of magnets

Abstract

5,10,15,20-Tetrakis(4-fluorophenyl)porphyrinatomanganese(III) tetracyanoethenide, [MnTFPP][TCNE], 1F, 5,10,15,20-tetrakis(4-bromophenyl)porphyrinatomanganese(III) tetracyanoethenide, [MnTBrPP][TCNE], 1Br, and 5,10,15,20-tetrakis(4-iodophenyl)porphyrinatomanganese(III) tetracyanoethenide, [MnTIPP][TCNE], 1I, have been prepared and characterized as both the toluene and dichloromethane disolvates and the magnetic, IR, and thermal properties of these solvates, as well as their corresponding desolvated materials, have been determined and are compared to the previously reported [TCNE]˙⁻ salts of 5,10,15,20-tetrakis(4-chlorophenyl)porphyrinatomanganese(III), 1Cl. The ν_CN absorptions of 1X·2PhMe (X = Cl, Br, I) and 1I·xxCH₂2Cl₂2 occur at 2202 ± 1 (m) and 2161 ± 1 (s) cm⁻¹ and 1X·xxCH₂2Cl₂2 (X = F, Cl, Br) and 1F·xxPhMe occur at 2195 ± 1 (m) and 2135 ± 2 (s) cm⁻¹. Upon thermolysis at 175 °C the toluene desolvates to form α-[MnTXPP][TCNE] [X = Cl (α-1C1), Br (α-1Br), I (α-1I)] with ν_CN absorptions maintained at 2201 ± 1 (m) and 2160 ± 1 (s) cm⁻¹. In contrast, unlike 1Cl·2PhMe, desolvation of 1X·2PhMe (X = Br, I) in refluxing n-octane (127 °C) or heated mineral oil (170 °C) slurries does not lead to materials with ν_CN absorptions characteristic of β-[MnTClPP][TCNE]. Upon facile desolvation of dichloromethane solvates, materials with ν_CN absorptions characteristic of γ-[MnTClPP][TCNE] form as the ν_CN absorptions remain essentially unchanged [2195 ± 2 (m) and 2135 ± 2 (s) cm⁻¹]. The magnetic data for the [MnTXPP][TCNE] family are consistent with linear chain ferrimagnets comprised of antiferromagnetically coupled S = 2 Mn^III sites and S = 1/2 [TCNE]˙⁻ sites with the antiferromagnetic intrachain coupling, J_intra/k_B (k_B = Boltzmann’s constant) determined from fits to the Seiden expression for isolated chains comprised of alternating S = 1/2 and S = 2 spins. For the [MnTFPP][TCNE] series, J_intra values of −225, −160, −210, and −177 K were obtained for 1F·xxPhMe, β-1F, 1F·2CH₂2Cl₂2, and γ-1F, respectively. While J_intra values of −30, −45, −270, and −75 K were observed for 1Br·2PhMe, α-1Br, 2CH₂2Cl₂2, and γ-1Br, respectively. Finally, J_intra values of −53, −35, −35, and −53 K were observed for 1I·2PhMe, α-1I, 1I·2CH₂2Cl₂2, and γ-1I, respectively. The ordering temperatures, T_c, determined from the maxima in the 10 Hz χ′(T) ranged from 6.5 K (1I·2PhMe) to 28 K for (1F·xxPhMe). Based on the magnetic behavior, desolvation of 1X·PhMe and 1X·CH₂2Cl₂2 increases the magnetic disorder and subsequent spin glass behavior as well as changing the observed interchain magnetic coupling.