Ferrimagnetic behavior of multiple phases and solvates of (meso-tetrakis(4-chlorophenyl)porphinato)manganese(III) tetracyanoethenide, [MnTClPP]+[TCNE]•-.: Enhancement of magnetic coupling by thermal annealing

被引:130
作者
Brandon, EJ [1 ]
Rittenberg, DK [1 ]
Arif, AM [1 ]
Miller, JS [1 ]
机构
[1] Univ Utah, Dept Chem, Salt Lake City, UT 84112 USA
关键词
D O I
10.1021/ic971521z
中图分类号
O61 [无机化学];
学科分类号
070301 ; 081704 ;
摘要
(meso-Tetrakis(4-chlorophenyl)porphinato)manganese(II) tetracyanoethenide, [MnTClPP][TCNE], has been prepared and structurally characterized as the toluene and dichloromethane disolvates, and the magnetic and thermal properties of these solvates, as well as their corresponding desolvates, have been determined. The ditoluene solvate (1) has a triclinic unit cell: P (1) over bar, a = 10.171(4) Angstrom, b = 10.189(3) Angstrom, c = 14.522 (3) Angstrom, alpha = 107.51(2)degrees beta = 85.58(2)degrees, gamma = 111.51(3)degrees, Z = 1. The bis(dichloromethane) solvate (2) belongs to the monoclinic unit cell: P2(1)/n, a = 9.894(2) Angstrom, b = 10.697(2) Angstrom, c = 23.560(5) Angstrom, beta = 101.34(2)degrees, Z = 2. The cation is typical with average Mn-N distances of 2.012 Angstrom for both the toluene and dichloromethane solvates. The bonding distances for both planar anions are characteristic of [TCNE](.-). Both solvates have an uniform linear chain (1-D) coordination-polymer structure comprised of alternating cations and anions. Each [TCNE](.-) binds to two Mn-III's in a trans-mu-N-sigma-bound manner with Mn-N spacings of 2.267 (1) and 2.276 Angstrom (2). The Mn-N-C angles are 167.2 and 143.1 degrees, while intrachain Mn Mn separations are 10.189 and 9.894 Angstrom, and the dihedral angle between the MnN4 and [TCNE](.-) mean planes are 86.8 and 52.4 degrees for 1 and 2, respectively. The upsilon(CN) absorptions for the toluene and dichloromethane solvates occur at 2201 m and 2160 s cm(-1) and 2195 m and 2138 s cm(-1), respectively. Upon thermolysis at 175 degrees C 1 desolvates to alpha-[MnTClPP][TCNE] with upsilon(CN) absorptions at 2201 m and 2159 s cm(-1) In contrast, desolvation of 1 in refluxing n-octane leads to beta-[MnTclPP][TCNE] with upsilon(CN) absorptions at 2190 m and 2132 s cm(-1). Upon facile desolvation of 2 to form gamma-[MnTClPP][TCNE] the nitrile absorptions remain essentially unchanged (2195 m and 2137 s cm(-1)). For 1 and a the susceptibilities can be fit by the Curie-Weiss expression with Theta = -60 K (T > 210 K) and -10 K (T > 250 K) and an effective Theta, Theta' of +13 (50 < T < 120 K) and 29 K (60 < T < 160 K), respectively. Theta is not observed for the 2 or the beta- or gamma-phase; however, Theta' for the 2 and the beta- and gamma-phases are 58, 92, and 86 K, respectively. The magnetic data 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/k(B) (k(B) = Boltzmann's constant) determined from fits to the Seiden expression, of -33, -160, -65, -267, and -265 K for the 1, 2, and alpha-, beta-, and gamma-phases, respectively. Hysteresis with a coercive field of 5.8 kOe is observed for 1 at 2 K. Metamagnetic behavior below 5 K is observed for the 1, 2, and beta- and gamma-phases with critical fields of 10, 27, 27, and 27 kOe, respectively. The ordering temperatures, T,, determined from the maxima in the chi'(T) data taken at 10 Hz, are 8.8, 6.7, 11.1, 14.1, and 11.4 K for the phases 1, alpha, beta, 2, and gamma, respectively. Desolvation of 1 and 2 increases the magnetic disorder and the magnetic coupling.
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页码:3376 / 3384
页数:9
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