Coordination Polymers Based on Diiron Tetrakis(dithiolato) Bridged by Alkali Metals, Electrical Bistability around Room Temperature, and Strong Antiferromagnetic Coupling

Abstract

Coordination polymer chains have been formed by the direct reaction between HSC6H2Cl2SH and FeCl3·6H2O in the presence of an aqueous solution of the corresponding alkali-metal hydroxide (M = Li, Na, and K) or carbonate (M = Rb and Cs). The structures consist of dimeric [Fe2(SC6H2Cl2S)4](2-) entities bridged by [M2(THF)4] [M = K (1), Rb (2), and Cs (3); THF = tetrahydrofuran] or {[Na2(μ-H2O)2(THF)2] (5 and 5') units. The smaller size of the lithium atom yields an anion/cation ion-pair molecule, [Li(THF)4]2[Fe2(SC6H2Cl2S)4] (4), in which the dianionic moieties are held together by Cl···Cl interactions. Electrical characterization of these compounds shows a general semiconductor behavior in which the conductivity and activation energies are mainly determined by the M-Cl and M-S bond distances. Compounds 1 and 5' are interesting examples of bistability showing reversible transitions centered at ca. 350 and 290 K with very large hysteresis of ca. 60 and 35 K, respectively. All of these compounds exhibit intradimer strong antiferromagnetic Fe···Fe interactions.

Synthesis and structural characterization of transition metal dithiolene derivatives containing divalent metals as counter-cations

“…The dianionic unit [Fe 2 (SC 6 H 2 Cl 2 S) 4 ] 2displays the same geometry as that previously found in related compounds where each iron atom shows the expected 4 + 1 squarepyramidal geometry. 16,17 The Fe-S, S-C and C-C distances (Table 1) are also in the range reported for analogous derivatives. [16][17][18][19][20][21][22][23] On the other hand, the Ca(II) atom is heptacoordinated by four acetone and three H 2 O molecules yielding to a distorted pentagonal bipyramidal geometry, with an O(1)-Ca(1)-O(4) angle of 169.4(2)° between the apical positions, and a range of 72.3(2)°-76.1(2)° for the angles between the equatorial ligands.…”

“…16,17 The Fe-S, S-C and C-C distances (Table 1) are also in the range reported for analogous derivatives. [16][17][18][19][20][21][22][23] On the other hand, the Ca(II) atom is heptacoordinated by four acetone and three H 2 O molecules yielding to a distorted pentagonal bipyramidal geometry, with an O(1)-Ca(1)-O(4) angle of 169.4(2)° between the apical positions, and a range of 72.3(2)°-76.1(2)° for the angles between the equatorial ligands. The Ca-O distances (Table 1) agree with those reported for similar Ca-O H2O bonds [24][25][26][27][28][29][30][31][32] and Ca-O acetone , [32][33][34] respectively.…”

“…different organic solvents, presence/absence of water). 16,17 In all of these CPs the positive charge density of the alkali complexes must match that of the [Fe 2 (SC 6 H 2 R 2 S) 4 ] 2-(R = Cl, H) anionic complexes and electron repulsive forces are present in the two monovalent cations of the entity [M 2 (µ-L) n ] 2+ (Scheme 1a). We have now tried to evaluate whether the use of divalent cation complexes as counter cations instead, could favor the formation of different coordination polymers, as they do not show these electron repulsive forces (Scheme 1b).…”

“…Recently, we have reported a series of coordination polymers containing the dianionic entities [Fe 2 (SC 6 H 2 R 2 S) 4 ] 2-(R = Cl, H) and [M 2 (µ-L) n ] 2+ (M = alkali metal) as counter-cations. 16,17 Taking into account these results we have considered of interest to study the possibility to form coordination polymers (CPs) containing cationic divalent metals instead, in order to evaluate their structural effects on the coordination metaldithiolene network rearrangement. Here we report on the reactions carried out between HSC 6 H 2 Cl 2 SH, FeCl 3 4 ]} 3, instead of the CPs formed in the analogous reactions using alkali metals instead.…”

“…Here we report on the reactions carried out between HSC 6 H 2 Cl 2 SH, FeCl 3 4 ]} 3, instead of the CPs formed in the analogous reactions using alkali metals instead. 16,17 Scheme 1. Electrostatic interactions taking place between an anionic 1D polymeric chain and monovalent (a) versus divalent cationic entities to counterbalance the charge (b).…”