The charge-transfer compound [{Ru(2)(O(2)CPh-o-Cl)(4)}(2)TCNQ(MeO)(2)] x CH(2)Cl(2) (1; o-ClPhCO(2)(-) = o-chlorobenzoate; TCNQ(MeO)(2) = 2,5-dimethoxy-7,7,8,8-tetracyanoquinodimethane) was synthesized from the reaction of the neutral precursors [Ru(2)(II,II)(O(2)CPh-o-Cl)(4)] (abbreviated as [Ru(2)(II,II)] or [Ru(2)(4+)]) and TCNQ(MeO)(2) in a CH(2)Cl(2)/nitrobenzene solution. The structure consists of two-dimensional layers consisting of an infinite array in which [Ru(2)(II,II)] units are involved in charge transfer to TCNQ(MeO)(2) to give a formal charge of [{Ru(2)(4.5+)}-TCNQ(MeO)(2)(*-)-{Ru(2)(4.5+)}]. Interstitial CH(2)Cl(2) molecules are located in the void spaces between the layers. Strong intralayer magnetic coupling between the units [Ru(2)(II,II)] with S = 1 or [Ru(2)(II,III)] with S = 3/2 and TCNQ(MeO)(2)(*-) with S = 1/2, as well as long-range ordering due to antiferromagnetic interlayer interactions, was observed. An antiferromagnetic ground state exists below T(N) = 75 K, which undergoes a metamagnetic transition under applied fields less than 2 T to a field-induced canted antiferromagnetic state with large coercivities up to H(c) = 1.6 T at 1.8 K. Compound 1 gradually loses the interstitial CH(2)Cl(2) molecule at room temperature to form a dried sample (1-dry) without loss of crystallinity and converts nearly reversibly back to 1 after being exposed to CH(2)Cl(2) vapor for 72 h (distinguished as 1'). Interestingly, during this process there is no significant change in lattice dimensions and bond distances or angles with a volume change of only 1.2 vol %. The only discernible difference is ordering/disordering of a pendant ligand orientation, but the magnetism is dramatically altered to a ferromagnetic state with T(c) approximately 56 K for 1-dry. The magnetic property changes are gradual and depend on the degree of interstitial CH(2)Cl(2) molecule loss with reversibility in the process of going between 1 and 1-dry. In addition, in the case of partially desolvated crystals that have mixed domains of ferromagnetically and antiferromagnetically ordered domains for desolvated and solvated segments, respectively, the complete change to ferromagnet can also be triggered by magnetic fields even if the desolvated segments are comparatively minor compared to the solvated segments in a crystal. Surprisingly, the information of the existence of ferromagnetically ordered domains is dynamically recorded in the entire crystal after applying significant magnetic fields as if the majority of the antiferromagnetically ordered domains for solvated segments were never present.

Neutral (N)-ionic (I) transitions in organic donor (D)/acceptor (A) charge-transfer complexes are intriguing because a 'reservoir of functions' is available. For systematically controlling N-I transitions, tuning the ionization potential of D and the electron affinity of A is extremely important. However, the effect of Coulomb interactions, which likely causes a number of charge-gap states at once in a system bringing about stepwise transitions, is a long-standing mystery. Here, we show definite evidence for stepwise N-I transitions caused by contributions from anisotropic interchain Coulomb interactions in a metal-complex-based covalently bonded DA chain compound, [Ru(2)(2,3,5,6-F(4)PhCO(2))(4)(DMDCNQI)]·2(p-xylene) (1; 2,3,5,6-F(4)PhCO(2)(-) = 2,3,5,6-tetrafluorobenzoate; DMDCNQI = 2,5-dimethyl-N,N'-dicyanoquinonediimine), where the [Ru(2)(II,II)(2,3,5,6-F(4)PhCO(2))(4)] moiety has a paddlewheel diruthenium(II,II) motif with a Ru-Ru bond. An intermediate-temperature phase involving self-organized N and I chains was observed in the temperature range between 210 K (= T(2)) and 270 K (= T(1)) with N phase at T > T(1) and I phase at T < T(2). Accompanying the charge transitions, the spin-ground states as well as the ferrimagnetic ordering in the I phase vary. The stepwise feature of the N-I transition with a highly sensitive magnetic response should bring about new dynamical functionalities associated with charge, spin, and lattice.

The isostructural series of two-dimensional (2-D) fishnet-type network compounds, [{Ru(2)(O(2)CCF(3))(4)}(2)(TCNQR(x))] x n(solv) (R(x) = H(4), 1; Br(2), 2; Cl(2), 3; F(2), 4; F(4), 5), has been synthesized from the reactions of a paddlewheel diruthenium(II, II) complex, [Ru(2)(II,II)(O(2)CCF(3))(4)], and neutral TCNQ derivatives (TCNQR(x) = 2,3,5,6- or 2,5-halogen-substituted 7,7,8,8-tetracyanoquinodimethane) under anaerobic conditions. Corresponding Rh compounds 1-Rh-5-Rh, which are diamagnetic and redox-inactive, were also synthesized for the purpose of comparison with 1-5. According to the electron affinity of TCNQR(x), which is related to its first reduction potential, the Ru(2) series (1-5) has the requisite driving force for charge transfer from [Ru(2)(II,II)(O(2)CCF(3))(4)] to TCNQR(x), which can lead to a mixed-valence state of [{Ru(2)(4.5+)}-(TCNQR(x)(*-))-{Ru(2)(4.5+)}] for the 2-D network. Such a charge (or electron) transfer results in magnetic exchange interactions between [Ru(2)] units (S = 1 for [Ru(2)(II,II)] and S = 3/2 for [Ru(2)(II,III)](+)) via TCNQR(x)(*-) S = 1/2 radicals that lead to long-range magnetic ordering in the layer. In the present series, only 5 demonstrated the full electron transfer (1-e(-) transfer) to the mixed-valence state, whereas other members are essentially in the state [{Ru(2)(4+)}-(TCNQR(x)(0))-{Ru(2)(4+)}]. Whereas 1-4 are paramagnetic, 5 is a metamagnet undergoing 3-D long-range antiferromagnetic ordering at 95 K (= T(N)) and reverts to a magnetic-field-induced ferromagnetic state exhibiting coercivity up to 60 K. This result is consistent with the fact that TCNQF(4) has the strongest electron affinity among the TCNQR(x) molecules. Even in neutral forms, however, 1-4 can be observed to undergo thermally and/or field-activated charge transfers from [Ru(2)(II,II)] to TCNQR(x) to give semiconductors with an activation energy of 200-300 meV, which is a driving force to transport electrons over the lattice. As determined by their conducting properties, the ease of thermally and/or field-activated charge transfers is on the order of 1 < 4 < 2 approximately = 3 << 5, which is in agreement with the order of electron affinity of TCNQR(x). Indeed, a magnetic anomaly with short-range order associated with the localization of charge-transferred electrons was revealed in the low-temperature susceptibility data for 2 and 3. Finally, 5 was subjected to terahertz time-domain spectroscopy, the data from which revealed that transport hopping electrons scattered at high temperatures interact with magnetically ordered spins with the scattering being suppressed at T(N), at which temperature the real part of the complex electronic conductivity (sigma(1)) and dielectric permeability (epsilon(1)) are dramatically altered. From these collective data, we conclude that molecular design based on an interunit charge transfer in a paramagnetic lattice is an efficient route to the design of materials with synergism between magnetic and conducting properties.

A series of isostructural cyano-bridged Mn(III)(h.s.)-M(III)(l.s.) alternating chains, [Mn(III)(5-TMAMsalen)M(III)(CN)(6)]⋅4H(2)O (5-TMAMsalen(2-)=N,N'-ethylenebis(5-trimethylammoniomethylsalicylideneiminate), Mn(III)(h.s.)=high-spin Mn(III), M(III)(l.s.)=low-spin Co(III), Mn-Co; Fe(III), Mn-Fe; Mn(III), Mn-Mn; Cr(III), Mn-Cr) was synthesized by assembling [Mn(III)(5-TMAMsalen)](3+) and [M(III)(CN)(6)](3-). The chains present in the four compounds, which crystallize in the monoclinic space group C2/c, are composed of an [-Mn(III)-NC-M(III)-CN-] repeating motif, for which the -NC-M(III)-CN- motif is provided by the [M(III)(CN)(6)](3-) moiety adopting a trans bridging mode between [Mn(III)(5-TMAMsalen)](3+) cations. The Mn(III) and M(III) ions occupy special crystallographic positions: a C(2) axis and an inversion center, respectively, forming a highly symmetrical chain with only one kind of cyano bridge. The Jahn-Teller axis of the Mn(III)(h.s.) ion is perpendicular to the N(2)O(2) plane formed by the 5-TMAMsalen tetradentate ligand. These Jahn-Teller axes are all perfectly aligned along the unique chain direction without a bending angle, although the chains are corrugated with an Mn-N(axis) -C angle of about 144°. In the crystal structures, the chains are well separated with the nearest inter-chain M⋅⋅⋅M distance being relatively large at 9 Å due to steric hindrance of the bulky trimethylammoniomethyl groups of the 5-TMAMsalen ligand. The magnetic properties of these compounds have been thoroughly studied. Mn-Fe and Mn-Mn display intra-chain ferromagnetic interactions, whereas Mn-Cr is characterized by an antiferromagnetic exchange that induces a ferrimagnetic spin arrangement along the chain. Detailed analyses of both static and dynamic magnetic properties have demonstrated without ambiguity the single-chain magnet (SCM) behavior of these three systems, whereas Mn-Co is merely paramagnetic with S(Mn)=2 and D/k(B)=-5.3 K (D being a zero-field splitting parameter). At low temperatures, the Mn-M compounds with M=Fe, Mn, and Cr display remarkably large M versus H hysteresis loops for applied magnetic fields along the easy magnetic direction that corresponds to the chain direction. The temperature dependence of the associated relaxation time for this series of compounds systematically exhibits a crossover between two Arrhenius laws corresponding to infinite-chain and finite-chain regimes for the SCM behavior. These isostructural hetero-spin SCMs offer a unique series of alternating [-Mn-NC-M-CN-] chains, enabling physicists to test theoretical SCM models between the Ising and Heisenberg limits.

A series of paddlewheel diruthenium(ii, ii) complexes with various fluorine-substituted benzoate ligands were isolated as THF adducts and structurally characterized: [Ru(2)(F(x)PhCO(2))(4)(THF)(2)] (F(x)PhCO(2)(-) = o-fluorobenzoate, o-F; m-fluorobenzoate, m-F; p-fluorobenzoate, p-F; 2,6-difluorobenzoate, 2,6-F(2); 3,4-difluorobenzoate, 3,4-F(2); 3,5-difluorobenzoate, 3,5-F(2); 2,3,4-trifluorobenzoate, 2,3,4-F(3); 2,3,6-trifluorobenzoate, 2,3,6-F(3); 2,4,5-trifluorobenzoate, 2,4,5-F(3); 2,4,6-trifluorobenzoate, 2,4,6-F(3); 3,4,5-trifluorobenzoate, 3,4,5-F(3); 2,3,4,5-tetrafluorobenzoate, 2,3,4,5-F(4); 2,3,5,6-tetrafluorobenzoate, 2,3,5,6-F(4); pentafluorobenzoate, F(5)). By adding fluorine atoms on the benzoate ligands, it was possible to tune the redox potential (E(1/2)) for [Ru(2)(II,II)]/[Ru(2)(II,III)](+) over a wide range of potentials from -40 mV to 350 mV (vs. Ag/Ag(+) in THF). 2,3,6-F(3), 2,3,4,5-F(4), 2,3,5,6-F(4) and F(5) were relatively air-stable compounds even though they are [Ru(2)(II,II)] species. The redox potential in THF was dependent on an electronic effect rather than on a structural (steric) effect of the o-F atoms, although more than one substituent in the m- and p-positions shifted E(1/2) to higher potentials in relation to the general Hammett equation. A quasi-Hammett parameter for an o-F atom (σ(o)) was estimated to be ∼0.2, and a plot of E(1/2)vs. a sum of Hammett parameters including σ(o) was linear. In addition, the HOMO energy levels, which was calculated based on atomic coordinates of solid-state structures, as well as the redox potential were affected by adding F atoms. Nevertheless, a steric contribution stabilizing their static structures in the solid state was present in addition to the electronic effect. On the basis of the electronic effect, the redox potential of these complexes is correlated to the HOMO energy level, and the electronic effect of F atoms is the main factor controlling the ionization potential of the complexes with ligands free from the rotational constraint, i.e. complexes in solution.

The design of dp-pp molecular systems with efficient electronic communication is a long-standing goal in the field of inorganic chemistry. Guiding principles for this research are provided by the seminal studies on the Creutz-Taube ion, [(H 3 N) 5 Ru(m-pyz)Ru(NH 3 ) 5 ] 5+ (pyz = pyrazine), discovered in 1969, [1] as well as subsequent related compounds [2] that undergo charge-transfer interactions between mixed-valent metal ions through an organic bridging ligand. Various experimental investigations to evaluate the electron-transfer dynamics were undertaken and theoretical interpretations from kinetic and, thermodynamic approaches were developed by Hush, [3] Marcus and Sutin, [4] and others.[5]In the context of the current work, we also note the important contributions of Crutchley and co-workers, who explored electron-transfer processes in dinuclear ruthenium-(III) complexes bridged by the 1,4-dicyanamidobenzene dianion (Dicyd 2À ) or one of its substituted derivatives. [6] Interestingly, this class of compounds demonstrated strong intramolecular magnetic coupling between Ru III S = 1/2 spins via the pp orbital of the Dicyd bridge with J exceeding 400 cm À1 closely associated with a highly conjugated p-d network, classified as Class II or III behavior on the RobinDay scale.[7] A crucial design ingredient for such systems is a 1:2 ratio of the one-electron donor (D, i.e., Dicyd) to the oneelectron acceptor (A, i.e., a Ru III ion) that can lead to an electron-transfer resonance of type [ ]. Our research is directed at the synthesis of coordination framework solids with dp/pp conjugation with the goal of achieving hybrid magnetic and conducting properties. In short, our research in this area can be expressed conceptually as "expanding the Creutz-Taube molecule to higher dimensions". The strategy is to design networks with a D:A ratio of 2:1 or 1:2 which involve a one-electron transfer that "turns on" electron-transfer resonance. In this vein, we chose to study the family of paddlewheel-type diruthenium(II,II) complexes with S = 1 as an electron donor to undergo the reversible redox reaction [Ru 2 II,II ]$[Ru 2 II,III ] without a significant change of structure.[8] The molecule concomitantly acts as a linear building block, [9] with 7,7,8,8-tetracyanoquinodimethane (TCNQ) acting as an electron acceptor and tetrakis-monodentate donor ligand. In earlier work, the 2:1 assemblies [{Ru 2 (O 2 CCF 3 )} 2 TCNQ]·3 S (S = toluene, 1 a;[10] pxylene, 1 b) [11] and [{Ru 2 (O 2 CCF 3 )} 2 TCNQF 4 ]·3 p-xylene (TCNQF 4 = 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane; 2), [11] with two-dimensional (2D) fishing-net-like (hexagonal) layered structures ( Figure 1) were synthesized.While 1 a and 1 b showed poor if any [Ru 2 ]!TCNQ electron transfer, 2 exhibited significant electron-transfer resonance which led to unusual magnetic properties, that is, the compound is a metamagnet with T N = 95 K (a field-induced ferromagnet), albeit not the high-T c ferromagnet that we were seeking.Herein we report a new structural type...

15 pagesInternational audienceSingle-chain magnets (SCMs) are one-dimensional systems in which the relaxation of the magnetization becomes very slow at low temperature. This singular behavior is due to the vicinity of the critical point located at vanishing temperature (T=0) and applied magnetic field (H=0). In order to optimize the properties of these nano-objects, detailed studies of the observed critical behavior are necessary. However, previous works on the SCM relaxation have essentially analyzed experimental data in the absence of applied magnetic field. We discuss in this paper the effect of applying a magnetic field on two different examples of single-chain magnets. These samples have been previously described in the absence of magnetic field and considered as model systems since their chains are composed of a regular one-dimensional (1D) arrangement of anisotropic trimer units. These magnetic trinuclear motifs can be described at low temperature as effective spins coupled ferromagnetically. Theoretical results relevant to analyze our data in the presence of an applied magnetic field are first described. We also present a simple numerical approach to discuss finite-size effects relevant in SCM systems. Experimental data, including ac and dc data on powder samples and single crystals, are then presented. These results are analyzed and compared with the theoretical predictions deduced for the 1D Ising model. At low field, for h1 where is the correlation length normalized to the unit cell parameter and h=~H/kBT is the dimensionless applied field or for hL1 when finite-size effects are relevant L being the chain length normalized to the unit cell parameter, we show that experimental data reproduce the critical behavior expected from the theory. Moreover, the obtained values of or L are in excellent agreement with the estimation deduced from susceptibility data. At higher fields, for h1 or hL1, we show that the field dependence of the relaxation time is drastically different for the two samples. This difference is understood taking into account the field dependence of the relaxation time of the effective spins located inside a domain wall

Iron(III) spin-crossover compounds with H3-OMe-salRen ligands [Fe(3-OMe-salRen)2]ClO4 (1–5) were prepared and characterized by single-crystal X-ray diffraction, Mössbauer spectra, magnetic susceptibilities, and electronic spectra, where 3-OMe-salRen is a tridentate ligand derived from 3-methoxysalicylaldehyde and N-R-ethylenediamine (R = H, Me, Et, Pr, and Bu for 1, 2, 3, 4, and 5). The structures of compounds 1, 2, 3, and 5 at 90 and 298 K, and that of compound 4 at 298 K were determined. Compounds 1, 2, 3, and 5 exhibited a spin transition depending on temperature; the transition temperatures for 1, 2, 3, and 5 were &gt;400, 360, 196, and 223 K, respectively. Compound 4 was in the high-spin state in the temperature range of 5 to 400 K. σ–π or π–π interactions exist in compounds 1–5, and the structures of the compounds were made clear in both the high-spin and low-spin states. Compound 3 exhibited a spin transition with thermal hysteresis.