Photomagnetic studies on spin-crossover solid solutions containing two different metal complexes, [Fe(1-bpp)2]x[M(terpy)2]1−x[BF4]2 (M = Ru or Co)

Abstract

The photomagnetic properties of two series of spin-crossover solid solutions, [Fe(1-bpp)(2)](x)[Ru(terpy)(2)](1-x)(BF(4))(2) and [Fe(1-bpp)(2)](x)[Co(terpy)(2)](1-x)(BF(4))(2) (1-bpp = 2,6-bis[pyrazol-1-yl]pyridine), have been investigated. For all the materials, the evolution of the T(LIESST) value, the high-spin → low-spin relaxation parameters and the LITH loops were thoroughly studied. Interestingly in the Fe:Co series, along the photo-excitation, cobalt ions are concomitantly converted from low-spin to high-spin states with the iron centres, and also fully relax after light excitation.

Doping ruthenium complexes into a molecular spin-crossover material

“…That is the expected trend, since the dopant molecule is larger than the iron complex, which is in turn larger in its high-spin state. Thus, a higher dopant concentration expands the crystal lattice [16] and stabilizes the high-spin state of the host material [27]. Second, the transition becomes less cooperative as x decreases.…”

“…None-the-less, it is clear that the host compound and the two dopant complexes retain their integrity during the 1-2 days required for the synthesis of the solid solutions described below. Following our previous protocol [15,17,18] [15][16][17][18], x was consistently higher by microanalysis than expected from the mole ratios of the complexes in the crystallization solutions. That may reflect a higher solubility of the ruthenium dopant compared to the iron complex, which therefore crystallizes preferentially.…”

“…Our initial work has produced homogeneous solid solutions of [Fe(bpp) 2 ][BF 4 ] 2 (bpp = 2,6-di{pyrazol-1-yl}pyridine) [14] with [M(terpy) 2 ][BF 4 ] 2 complexes (terpy = 2,2':6',2"-terpyridine; M = Ru [15,16], Co [16,17] or Cu [18]; Scheme 1). This work afforded solid materials exhibiting both spin-crossover with fluorescence, albeit at different temperatures [15], and the first observation of allosteric switching of two different spin-crossover centers in the same material [17] 2 dopants are particularly suited to each other because they have the same molecular symmetry and charge balance; their cations are similar (but not identical) in size and shape; and, although they are not isostructural, the two compounds adopt the same type of "terpyridine embrace" crystal packing motif [15].…”

Spin-crossover and the LIESST effect in [Fe Co1‒(bpp)2][BF4]2 (1.00 ≤x≤ 0.77). Comparison with bifunctional solid solutions of iron and cobalt spin-crossover centers

“…The method exploits the fact that spin-crossover complexes of the [Fe(bpp) 2 ]X 2 type (bpp = 2,6-di{pyrazol-1-yl}pyridine; X = BF 4 -or ClO 4 -) often adopt the "terpyridine embrace" crystal packing [30], which is also exhibited by functional complexes of other tris-heterocyclic ligands such as [M(terpy) 2 ] 2+ (terpy = 2,2':6',2''-terpyridine) [31]. Although they are not perfectly isostructural as pure compounds, [Fe(bpp) 2 4 ] 2 materials that show both spin-crossover and fluorescence (M = Ru) [25,26], or exhibit allosteric switching of two different spin-crossover centers in the same material (M = Co) [26,27].…”

“…Six years ago we introduced a new approach towards this goal by doping functional complex cations into a spin-crossover host lattice [25][26][27][28][29]. The method exploits the fact that spin-crossover complexes of the [Fe(bpp) 2 ]X 2 type (bpp = 2,6-di{pyrazol-1-yl}pyridine; X = BF 4 -or ClO 4 -) often adopt the "terpyridine embrace" crystal packing [30], which is also exhibited by functional complexes of other tris-heterocyclic ligands such as [M(terpy) 2 ] 2+ (terpy = 2,2':6',2''-terpyridine) [31].…”