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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 ] •−
Author(s) -
Johnson Mitchell T.,
Arif Atta M.,
Miller Joel S.
Publication year - 2000
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/1099-0682(200008)2000:8<1781::aid-ejic1781>3.0.co;2-n
Subject(s) - chemistry , monoclinic crystal system , crystallography , dihedral angle , crystal structure , moiety , stereochemistry , methylene , ring (chemistry) , magnetic susceptibility , molecule , medicinal chemistry , hydrogen bond , organic chemistry
The crystal structure of meso ‐tetrakis(3,4,5‐trimethoxyphenyl)porphinatomanganese(III) 2,3,5,6‐tetrafluoro‐7,7,8,8‐tetracyanoquinodimethenide, [MnT(MeO) 3 PP][TCNQF 4 ]·3( o ‐C 6 H 4 Cl 2 ), 1· 3C 6 H 4 Cl 2 , provides the first example of a nondimeric [TCNQF 4 ] · – that is stabilized by trans ‐μ‐coordination to Mn III . Compound 1· 3C 6 H 4 Cl 2 crystallizes in the monoclinic C 2/ c space group [ a = 16.9486(10) Å, b = 25.7170(14) Å, c = 19.4009(12) Å, β = 107.091(4)°, V = 8082.8(8) Å 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 ν 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 Å, which is 0.038 Å longer than that for TCNQF 4 . 1· 3C 6 H 4 Cl 2 forms 1‐D zigzag chains of alternating 1 + and [TCNQF 4 ] · – , where the Mn III atoms are bound in a trans ‐ μ ‐fashion with Mn–N and intrachain Mn ··· Mn distances of 2.321(3) Å and 12.685 (4) Å, respectively. The MnNC angle and the dihedral angle between the [TCNQF 4 ] · – and the mean MnN 4 planes are 135.9(2)° and 46.4°, respectively, with the phenyl rings rotated 80° with respect to the mean porphyrin plane. The magnetic susceptibility of 1· 2.3C 6 H 4 Cl 2 can be calculated from the Curie–Weiss expression with θ = –37 K ( T > 250 K) and θ′ = +29 K (75 < T < 200 K) with an observed minimum in χ 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 = 3/2 system. The intrachain antiferromagnetic coupling, J /k B , is –71 K (–49 cm –1 ; –61 meV) based on a fit to the Seiden expression for noninteracting chains comprised of alternating quantum ( S = 1/2) and classical ( S > 1/2) spins, and the Hamiltonian H = –2 JS a · S b . Compound 1· 2.3C 6 H 4 Cl 2 ferrimagnetically orders at 7.3 K [based on the maxima in the 10 Hz χ′(T) data]. Hysteresis is observed at 2 K with coercive field, H cr , of 17.1 kOe and remnant magnetization of 7.200 emuOe/mol; hysteresis is not observed at 5 K. This compound also displays metamagnetic behavior at 2 K above a critical field of 20.2 kOe. The frequency‐dependent transitions observed in the χ′(T) and χ"(T) a.c. data are attributed to the transition to a spin glass or superparamagnetic state.