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Thermal- and photoinduced spin-state switching in an unprecedented three-dimensional bimetallic coordination polymer.

Niel, V. and Thompson, A. L. and Goeta, A. E. and Enachescu, C. and Hauser, A. and Galet, A. and Munoz, M. C. and Real, J. A. (2005) 'Thermal- and photoinduced spin-state switching in an unprecedented three-dimensional bimetallic coordination polymer.', Chemistry : a European journal., 11 (7). pp. 2047-2060.

Abstract

The compound {Fe(pmd)[Ag(CN)(2)][Ag-2(CN)(3)]} (pmd = pyrimidine) was synthesized and characterized. Magnetic, calorimetric and single crystal visible spectroscopic studies demonstrate the occurrence of a two-step high-spin (HS) = low-spin (LS) transition. The critical temperatures are, T,, = 185 and T,, = 148 K. Each step involves similar to 50% of the iron centers, with the low-temperature step showing a hysteresis of 2.5 K. The enthalpy and entropy variations associated with the two steps are Delta H-1 = 3.6 +/- 0.4 kJ mol(-1) and Delta S-1 = 19.5 +/- 3 J K-1 mol(-1); Delta H-2 = 4.8 +/- 10.4 kJ mol(-1) and Delta S-2 = 33.5 +/- 3 JK(-1) mol(-1). Photomagnetic and visible spectroscopy experiments show that below 50 K, where the LS state is the thermodynamically stable state, the compound can be switched quantitatively to the HS state using green-red light (550-650 nm). HS-to-LS relaxation experiments in the dark at temperatures between 15 and 55 K show that the relaxation takes place via a two-step cooperative process, which was analyzed in the context of the mean field theory. ne crystal structure has been studied at 290, 220, 170, 90 and 30 K together with 30 K after irradiation. ne compound adopts monoclinic symmetry (P2(l)/c, Z = 16) at all temperatures. There are five [FeN6] pseudo-octahedral sites linked by pmd, [Ag(CN)(2)](-) and [Ag2(CN)(3)](-) bridging ligands to form an unprecedented three-dimensional (6,6) topology. The structural analysis allows for an understanding of the microscopic mechanism of the two-step behavior of the thermally induced spin transition as well as the corresponding relaxation of the photoexcited compound based on the individual changes of the five sites. Synergy between metallophilic interactions and the spin transition is also shown by the variation of the (AgAg)-Ag-... distances. Correlations between the variation of the unit-cell volume and the change of (AgAg)-Ag-... interactions within each step with the asymmetric change of the anomalous heat capacity have also been inferred.

Item Type:Article
Additional Information:ISI:000227933800008
Keywords:Argentophilic interactions, Coordination modes, Polymers, Spin crossover.
Full text:Full text not available from this repository.
Publisher Web site:http://dx.doi.org/10.1002/chem.200400930
Record Created:10 Apr 2007
Last Modified:08 Apr 2009 16:29

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