Evolution of Spin-Crossover Transition in Hybrid Crystals Involving Cationic Iron Complexes [Fe(III)(3-OMesal2-trien)]+ and Anionic Gold Bis(dithiolene) Complexes Au(dmit)2 and Au(dddt)2

Abstract

Hybrid ion-pair crystals involving hexadentate [Fe(III)(3-OMesal 2 -trien)] + spin-crossover (SCO) cationic complexes and anionic gold complexes [Au(dmit) 2 ] − (1) (dmit = 4,5-dithiolato-1,3dithiole-2-thione) and [Au(dddt) 2 ] − (2) (dddt = 5,6-dihydro-1,4-dithiin-2,3-dithiolate) were synthesized and studied by single-crystal X-ray diffraction, P-XRD, and SQUID magnetometry. Our study shows that both complexes have similar 1:1 stoichiometry but different symmetry and crystal packing. Complex 1 has a rigid structure in which the SCO cations are engaged in strong π-interplay with molecular surrounding and does not show SCO transition while 2 demonstrates a reversible transition at T sco = 118 K in a much "softer", hydrogen-bonded structure. A new structural indicator of spin state in [Fe(sal 2 -trien)] + complexes based on conformational analysis has been proposed. Aging and thermocycling ruined the SCO transition increasing the residual HS fraction from 14 to 41%. Magnetic response of 1 is explained by the AFM coupled dimers S = 5/2 with J 1 = −0.18 cm −1 . Residual high-spin fraction of 2, apart from a contribution of the weak dimers with J 12 = J 34 = −0.29 cm −1 , is characterized by a stronger interdimer coupling of J 23 = −1.69 cm −1 , which is discussed in terms of possible involvement of neutral radicals [Au(dddt) 2 ].have been undertaken to use the SCO compounds in magnetic memory or display devices, as well as multi-modal sensors [4][5][6]. Moreover, polyfunctional compounds combining the conductivity and the spin-crossover transition have been highlighted in connection with spin-dependent transport and single molecular switching [7][8][9]. Spin-lattice relaxation in the low-dimensional conducting networks of centrosymmetrical molecules is strongly suppressed. The hybrid structures implementing efficient exchange interaction between the SCO and conducting subsystems would facilitate the development of new molecular spintronic devices where the spin transport is controlled by spin-crossover complexes.Metal bis-1,2-dithiolene complexes, as organic donors and acceptors, possess a delocalized electron system as a planar central core M(C 2 S 2 ) 2 and present different formal oxidation states. This type of complex has been intensively studied as a component of molecular conductors [10][11][12]. In addition, metal dithiolene complexes have a rich variety of physical properties, such as Peierls instability of the low-dimensional systems and the quantum fluctuations [10,13]. Thus, both SCO and metal dithiolene complexes could undergo phase transition, and combining two components in one crystal structure might give rise to a novel molecular material with exotic phenomena.The interplay between spin-crossover and conductivity was already observed in some of such materials [14][15][16]. The majority of conducting SCO compounds are represented by the Fe(III) cation complexes with [M(dmit) 2 ] δ− anions [17-19]. As a first step in this way, Faulmann et al. have published a simple salt [Fe(sal 2 -trien)][Ni(dmit) 2 ] ...

Magnetism, Conductivity and Spin-Spin Interactions in Layered Hybrid Structure of Anionic Radicals [Ni(dmit)2] Alternated by Iron(III) Spin-Crossover Complex [Fe(III)(3-OMe-Sal2trien)] and Ferric Moiety Precursors

“…We suppose that the absence in complex 1 of a spin-crossover to a low-spin state at cooling down to 120 K is associated with strong π…π and π…S intermolecular interaction of the magnetic cation (involving both salicylidene moieties of the ligand) with the molecular environment ( Figure 4) which prevents conformational changes necessary for a spin transition. Exactly the same situation was observed in the isostructural to 1 complex [Fe(III)(3-OMe-Sal2trien)][Au(dmit)2] [10]. The main difference between these two complexes is diverse valence of the metal ion in the M(dmit)2ˉ anion, Ni(II) and Au(III), respectively, according to which the charge state of dmit is not the same: 1.5 − in 1 and 2 − in the complex with Au.…”

“…Adjacent dimers are shifted along the long molecular axis, and there is no interdimer overlapping. However, the shortened S…S interdimer contacts [3.256(1), 3.387(1), 3.521(1), 3.619(1) Å] are observed, and they link the dimers into infinite ribbons along the [1][2][3][4][5][6][7][8][9][10] direction. Interplane distance between the nearest anions from the adjacent ribbons is 3.60(1) Å, and S…S contacts < 3.7 Å are absent.…”

“…The obtuse dihedral angle α between two salicylidene groups of 3-OMe-Sal 2 trien of 94.39 (6) • also points to a high-spin state of the complex (Figure 5a). Besides, we have shown recently that different conformations of the trien moiety are energetically favorable for HS and LS complexes and can be used as an indicator of spin state of [Fe(III)(sal 2 trien)] + cations [10,25]. In 1, the central -CH 2 -CH 2 -bond (ii) of the trien is near-normal to the side bonds (i, iii) that is typical for the HS state ( Figure 5a and Table 1).…”

“…The coexistence of conductivity and SCO properties in a combined hybrid structure opens promising prospective of their mutual synergy. For example, exchange interactions between delocalized spin moments of the conduction electrons and local magnetic moments of HS Fe(III) ions would facilitate ferromagnetic (FM) or antiferromagnetic (AFM) coupling in the SCO sublattice [10,11], which, in turn, may lead to a switchable spin-dependent transport in M(dmit) 2 sublattice. Therefore, conducting SCO materials are the prospective candidates for molecular spintronics [12][13][14].…”

Synthesis and Applications of New Spin Crossover Compounds

“…The R-sal 2 333 ligands promoting SCO in Fe(III) sites both in the solid state and in solution was established [20]. The hybrid ion-pair crystals containing hexadentate [Fe(III)(3-OMesal 2 -trien)] + SCO cationic coordination units and anionic gold complex units [Au(dmit) 2 ] − and [Au(dddt) 2 ] − were investigated by a single-crystal X-ray diffraction method, P-XRD, and SQUID measurements [21]. Fe(III) SCO compounds from qsal ligand (Hqsal = N-(8-quinolyl)salicylaldimine) were described.…”