ISSN:
0947-6539
Keywords:
electron transfer
;
magnetic properties
;
metalloporphryins
;
polymers
;
spin density
;
Chemistry
;
General Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
[MnIIITtBuPP]+[C4(CN)6].- · 5PhMe [MnIIITtBuPP = meso-tetrakis-(4′-tert-butylphenyl)porphinatomanganese(III)] has been prepared and structurally and magnetically characterized. The uniform, linear-chain (1-D) coordination polymer comprises alternating cations and anions. The bond lengths in planar ion [C4(CN)6].-]'- are 1.377(10) (CC-CC), 1.418(7) (C-CCC), 1.414 (C-CN), 1.457 (C-CNMn), 1.150 (C≡N), and 1.134 Å (C = NMn). The Mn-N-C angle is 172.3(4)°, and the intrachain Mn - Mn separation is 10.685 Å. Each [C4(CN)6].-]' unit is bonded to two MnIII atoms through the interior nitrogen atoms in a trans-μ2-N-σ manner with N-Mn bond lengths of 2.353 Å. The ṽCN absorptions are at 2217 (w, br) and 2190 (m) cm-1. Above 50 K the magnetic susceptibility of [MnIIITtBuPP]+[C4(CN)6].- can be fitted to the Curie-Weiss expression, χ∝1(T - θ), with an effective θ of -13 K. This is consistent with weak antiferromagnetic coupling, which is in contrast to the effective θ of +67 K for the uniform chain [MnIIIOEP]+[C4(CN)6].- [OEP = octaethylporphinato]. Here, the [C4(CN)6].-'- units are bonded to the MnIII centers through endo CN nitrogen atoms in a similar trans-μ2 manner. Density functional theory MO calculations reveal that the spin density of the CN nitrogen atom bound to [MnIIITtBuPP]+ (0.019 μBÅ-3) is significantly lower than that of the N atom bound to [MnIIIOEP]+ (0.102 μBÅ-3). This is consistent with the reduced spin coupling observed for [MnIIITtBuPP]+[C4(CN)6].-with respect to [MnIIITtBuPP]+[C4(CN)6].-, as evidenced by the lower θ value. The different orientations of the [C4(CN)6].- units - almost perpendicular (84.72°) for [MnIIITtBuPP]+[C4(CN)6].- and substantially tilted (32.1°) for [MnIIIOEP]+ [C4(CN)6].- may also contribute to the poorer overlap and weaker spin coupling. Hence, binding between sites with large spin densities is needed to stabilize strong ferromagnetic coupling.
Additional Material:
4 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/chem.19970030121
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