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The importance of m...
The importance of magnetic coupling through atoms with large spin densities - Structure and magnetic properties of meso-tetrakis-(4'-tert-butylphenyl)porphinatomanganese(III) hexacyanobutadienide, Mn(III)TtBuPP (+) C-4(CN)(6) (.-)
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Sugiura, K. (författare)
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Arif, A. M. (författare)
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Rittenberg, D. K. (författare)
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visa fler...
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Schweizer, J. (författare)
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- Öhrström, Lars, 1963 (författare)
- Chalmers tekniska högskola,Chalmers University of Technology
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Epstein, A. J. (författare)
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Miller, J. S. (författare)
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visa färre...
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(creator_code:org_t)
- 1997
- 1997
- Engelska.
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Ingår i: Chemistry-a European Journal. ; 3:1, s. 138-142
- Relaterad länk:
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https://research.cha...
Abstract
Ämnesord
Stäng
- [Mn(III)TtBuPP](+)[C-4(CN)(6)](.-) . [(MnTrBuPP)-Tr-III = 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 [C-4(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 Angstrom (C=NMn). The Mn-N-C angle is 172.3 (4)degrees, and the intrachain Mn ... Mn separation is 10.655 Angstrom. Each [C-4(CN)(6)](.-) unit is bonded to two Mn-III atoms through the interior nitrogen atoms in a times-mu(2)-N-sigma manner with N-Mn bond lengths of 2.353 Angstrom. The (CN) absorptions are at 2217 (w,br) and 2190 (m) cm(-1). Above 50 K the magnetic susceptibility of [Mn(III)TtBuPP](+)[C-4(CN)(6)](.-) can be fitted to the Curie-Weiss expression, chi proportional to 1/(T - theta), with an effective theta of -13 K. This is consistent with weak antiferromagnetic coupling, which is in contrast to the effective theta of + 67 K for the uniform chain [(MnOEP)-O-III](+)[C-4(CN)(6)](.-) [OEP = octaethylporphinato]. Here, the [C-4(CN)(6)](.-) units are bonded to the Mn-III centers through endo CN nitrogen atoms in a similar trans-mu(2) manner. Density functional theory MO calculations reveal that the spin density of the CN nitrogen atom bound to [Mn-III- TtBuPP](+) (0.019 mu(B) Angstrom(-3)) is significantly lower than that of the N atom bound to [(MnOEP)-O-III]+ (0.102 mu(B) Angstrom(-3)). This is consistent with the reduced spin coupling observed for [Mn(III)TtBuPP](+)[C-4(CN)(6)](.-) with respect to [(MnOEP)-O-III](+)[C-4(CN)(6)](.-), as evidenced by the lower theta value. The different orientations of the [C-4(CN)(6)](.-) units-almost perpendicular (84.72 degrees) for [Mn(III)TtBuPP](+)[C-4(CN)(6)](.-) and substantially tilted (32.1 degrees) for [(MnOEP)-O-III](+)[C-4(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.
Ämnesord
- NATURVETENSKAP -- Kemi (hsv//swe)
- NATURAL SCIENCES -- Chemical Sciences (hsv//eng)
Nyckelord
- polymers
- porphyrin
- exchange
- polarized neutron-diffraction
- molecular magnets
- metalloporphyrins
- charge-transfer complexes
- behavior
- tetracyanoethenide
- electron transfer
- spin density
- ferromagnetic
- oxidation
- chain
- magnetic properties
- <tcne>(center-dot-)
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