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A series of photoswitchable precursors based on [Fe(NCX)2L(L′)2], where X = S or Se, L is a bidentate ligand (phenanthroline or bipyrimidine), and L′ a monodentate ligand such as a pyridine or picoline derivative, were synthesized and their spin crossover (SCO) properties investigated in detail. The thermal and light‐induced magnetic properties of a family of [Fe(NCS)2L(py)2] [py = pyridine and L = bipyrimidine (1) or phenanthroline (phen) (2)] is reported. The [Fe(NCX)2(phen)(L′)2] compounds were further explored by changing the counteranion from NCS– to NCSe– (3) or by replacing pyridine with 4‐picoline (4) or 4‐ethylpyridine (5). Complexes 1–4 exhibit thermal and light‐induced SCO, while 5 remains in the high‐spin state. The kinetics governing the photoinduced back‐conversion was investigated for compounds 2 and 4. Complex 2 exhibits LIESST relaxation kinetics involving strongly cooperative (sigmoidal) behavior, whereas complex 4 displays a stretched exponential shape, typical for broad distributions of relaxation times. These results are discussed on the basis of the steric hindrance due to bulkiness and the electronic influence of the substituent effects on the magnetic and photomagnetic properties of mononuclear iron(II) complexes. [ABSTRACT FROM AUTHOR]

The thermal and light‐induced magnetic properties of a family of metal‐diluted spin‐crossover complexes, [FexM1–x(phen)2(NCS)2] (phen = 1,10‐phenantholine and M = NiII, CdII), are reported and compared to previous results obtained for the same series but with ZnII ions used to substitute FeII ions; the ultimate goal was to validate the influence of the size and nature of the inert metal ion on the light‐induced properties of spin‐crossover compounds. For all of the materials, we measured the thermally induced spin‐crossover temperature (T1/2) and T(LIESST) (LIESST = light‐induced excited spin‐state trapping) values systematically. We observed clearly that the dilution has a strong effect on the magnetic and photomagnetic properties. The magnitude of these effects depends strongly on the nature of the diluting metal. This comparison gives insights into the effect of the size of the diluting ion on T(LIESST) and T1/2 and completes the previous studies on the effect of internal pressure on the lifetime of the photoinduced state. [ABSTRACT FROM AUTHOR]

A new 1D polymeric copper(II) complex [{Cu(L)(CFCOO)}] has been synthesized using a potentially tetradentate Schiff base ligand, HL, ((E)-2-((pyridin-2-yl)methyleneamino)-5-chlorobenzoic acid) and characterized by different spectroscopic methods. Single crystal X-ray structural characterization reveals that the side arm carboxylate group of the coordinated Schiff base exhibits a μ-bridging mode and connects the neighbouring copper(II) ions leading to a zigzag 1D chain structure where the copper(II) ions display distorted square pyramidal geometries. Variable temperature magnetic susceptibility measurement reveals a weak antiferromagnetic exchange ( J = −0.47 ± 0.01 cm) prevails between copper(II) ions in the chain mediated by the bridging carboxylate group, is also supported by the room temperature EPR spectral study. Electrochemical property of the complex is also reported. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

The insertion of the [FeII(pyimH)3]2+ [pyimH = 2-(1 H-imidazol-2-yl)pyridine] spin-crossover complex into a ferromagnetic bimetallic oxalate network affords the hybrid compound [FeII(pyimH)3][MnIICrIII(ox)3]2 ·X (ox = C2O42-). This spin-crossover complex templates the growth of crystals formed by a chiral 3D oxalate network. The magnetic properties of this hybrid magnet show the coexistence of long-range ferromagnetic ordering at 4.5 K and a spin crossover of the intercalated [FeII(pyimH)3]2+ complex above 250 K. The compound presents a light-induced excited spin-state trapping (LIESST) effect below 60 K although with limited photoconversion (less than 8 %). [ABSTRACT FROM AUTHOR]

This work illustrates in detail the reversible hydration-dehydration process of a molecule-based material, which involves a drastic change of the switchable magnetic properties of the sample. Concretely, the complex [FeL222N3O2(CN)2] ·H2O exhibits a spin crossover (SCO) accompanied by a change of the coordination number. The dehydration and rehydration of this SCO complex was carried out and monitored by different methods, which include X-ray diffraction analysis. The corresponding samples display a thermal spin transition as well as a thermal quenching of the metastable high-spin state at low temperature. In particular it was observed that the rehydrated material exhibits a particularly high temperature of relaxation, T(TIESST), of the metastable high-spin state. On the other hand, it was shown that this compound exhibits a uncommon correlation between T(TIESST) and the thermal SCO, as compared with other spin-crossover compounds that do not exhibit a change in coordination number. [ABSTRACT FROM AUTHOR]

Two new isostructural iron(II) spin-crossover (SCO) framework (SCOF) materials of the type [Fe(dpms)2(NCX)2] (dpms=4,4′-dipyridylmethyl sulfide; X=S ( SCOF-6(S)), X=Se ( SCOF-6(Se))) have been synthesized. The 2D framework materials consist of undulating and interpenetrated rhomboid (4,4) nets. SCOF-6(S) displays an incomplete SCO transition with only approximately 30 % conversion of high-spin (HS) to low-spin iron(II) sites over the temperature range 300-4 K ( T1/2=75 K). In contrast, the NCSe− analogue, SCOF-6(Se), displays a complete SCO transition ( T1/2=135 K). Photomagnetic characterizations reveal quantitative light- induced excited spin-state trapping (LIESST) of metastable HS iron(II) sites at 10 K. The temperature at which the photoinduced stored information is erased is 58 and 50 K for SCOF-6(S) and SCOF-6(Se), respectively. Variable-pressure magnetic measurements were performed on SCOF-6(S), revealing that with increasing pressure both the T1/2 value and the extent of spin conversion are increased; with pressures exceeding 5.2 kbar a complete thermal transition is achieved. This study confirms that kinetic trapping effects are responsible for hindering a complete thermally induced spin transition in SCOF-6(S) at ambient pressure due to an interplay between close T1/2 and T(LIESST) values. [ABSTRACT FROM AUTHOR]

The two-step spin crossover in mononuclear iron(III) complex [Fe(salpm)2]ClO4 ⋅0.5 EtOH ( 1) is shown to be accompanied by a structural phase transition as concluded from 57Fe Mössbauer spectroscopy and single crystal X-ray diffraction, with spin-state ordering on just one of two sub-lattices in the intermediate magnetic and structural phase. The complex also exhibits thermal- and light-induced spin-state trapping (TIESST and LIESST), and relaxation from the LIESST and TIESST excited states occurs via the broken symmetry intermediate phase. Two relaxation events are evident in both experiments, that is, two T(LIESST) and two T(TIESST) values are recorded. The change in symmetry which accompanies the TIESST effect was followed in real time using single crystal diffraction. After flash freezing at 15 K the crystal was warmed to 40 K at which temperature superstructure reflections were observed to appear and disappear within a 10 000 s time range. In the frame of the international year of crystallography, these results illustrate how X-ray diffraction makes it possible to understand complex ordering phenomena. [ABSTRACT FROM AUTHOR]

We report on the syntheses, crystal structures, and magnetic properties of two cyano-bridged molecular assemblies: [Cu(phen)[sub3]][sub2]([Cu[supII](phen)[sub2]][sub2][W[supV](CN)[sub8]][sub2])(ClO[sub4])[sub2] ∙ 10H[sub2]O (phen 1 ,10-phenanthroline) (1) and ([Cu(supII](bpy)[sub2]][sub2][W[supV]((CN)[sub8]]) ([Cu[supII](bpy)[sub2]][W[supV](CN)[sub8]]) ∙ 4H[sub2]O (bpy = 2,2'-bipyridyl) (2). Compound 1 consists of cyano-bridged [Cu[supII][sub2]W[supV][sup+] molecular rectangles and isolated [Cu[supII][sub2]W[supV][sub2]] complexes. The molecular structure of 2 reveals cyano-bridged trinuclear [Cu[supII][sub2]W[supV]][sup+] and dinuclear [Cu[supII]W[supV]] ions. Magnetic interactions in 1 are interpreted in terms of the model of a tetranuclear moiety consisting of two ferromagnetic [Cu[supll]—NC—W[supV]] units (J[sub1] = +39(4) cm1) interacting antiferromagnetically (J[sub2] = -1.6(4) cm[sup-1]). The analysis of the magnetic response of 2 reveals ferromagnetic interaction within the [Cu[supll]—NC—W[supV]]—CN—Cu[supII] and [Cu[supll]—NC—W[supV]]- isolated units, characterized by J = +35(7) cm[sup-1] and antiferromagnetic coupling between them (4f = -0.30(8) cm[sup-1]). The discussion of the magnetic behavior and the correlation of the J[subCuW] parameters with the geometry of cyano bridges at copper(Il) centers of 1 and 2 is based on the DFT calculations, which yield J[subav] = +13.2 cm[sup-1] for 1 and J = +31 cm[sup-1] for 2. The domination of the ferromagnetic Cu[supII]—NC—W[supV] interaction in 1 and 2 originates from the mutual orthogonality of naturalmagnetic orbitals in the case of coordination of cyano bridges at the equatorial sites of Cu(ll) moieties. [ABSTRACT FROM AUTHOR]

The thermal and light‐induced magnetic properties of a family of metal‐diluted spin‐crossover complexes, [FexM1–x(phen)2(NCS)2] (phen = 1,10‐phenantholine and M = NiII, CdII), are reported and compared to previous results obtained for the same series but with ZnII ions used to substitute FeII ions; the ultimate goal was to validate the influence of the size and nature of the inert metal ion on the light‐induced properties of spin‐crossover compounds. For all of the materials, we measured the thermally induced spin‐crossover temperature (T1/2) and T(LIESST) (LIESST = light‐induced excited spin‐state trapping) values systematically. We observed clearly that the dilution has a strong effect on the magnetic and photomagnetic properties. The magnitude of these effects depends strongly on the nature of the diluting metal. This comparison gives insights into the effect of the size of the diluting ion on T(LIESST) and T1/2 and completes the previous studies on the effect of internal pressure on the lifetime of the photoinduced state. [ABSTRACT FROM AUTHOR]

The insertion of a [Fe(sal2-trien)]+ complex cation into a 2D oxalate network in the presence of different solvents results in a family of hybrid magnets with coexistence of magnetic ordering and photoinduced spin-crossover (LIESST effect) in compounds [FeIII(sal2-trien)][MnIICrIII(ox)3]·CHCl3 (1·CHCl3), [FeIII(sal2-trien)][MnIICrIII(ox)3]·CHBr3 (1·CHBr3), and [FeIII(sal2-trien)][MnIICrIII(ox)3]·CH2Br2 (1·CH2Br2). The three compounds crystallize in a 2D honeycomb anionic layer formed by MnII and CrIII ions linked through oxalate ligands and a layer of [Fe(sal2-trien)]+ complexes and solvent molecules (CHCl3, CHBr3, or CH2Br2) intercalated between the 2D oxalate network. The magnetic properties and Mössbauer spectroscopy indicate that they undergo long-range ferromagnetic ordering at 5.6 K and a spin crossover of the intercalated [Fe(sal2-trien)]+ complexes at different temperatures T1/2. The three compounds present a LIESST effect with a relaxation temperature TLIESST inversely proportional to T1/2. The isostructural paramagnetic compound, [FeIII(sal2-trien)][ZnIICrIII(ox)3]·CH2Cl2 (2·CH2Cl2) was also prepared. This compound presents a partial spin crossover of the inserted FeIII complex as well as a LIESST effect. Finally, spectroscopic characterization of the FeIII doped compound [Ga0.99Fe0.01(sal2trien)][MnIICrIII(ox)3]·CH2Cl2 (3·CH2Cl2) shows a gradual and complete thermal spin crossover and a LIESST effect on the isolated FeIII complexes. This result confirms that cooperativity is not a necessary condition to observe the LIESST effect in an FeIII compound. [ABSTRACT FROM AUTHOR]

Abstract: The synthesis, crystal structures and magnetic properties of two different copper(II) complexes of formula [Cu(L1)(dca)] n · nClO4 (1) and [Cu(L2)]2(dca)(ClO4) (2) [L1 = N,N-dimethylethylene-N′-(pyridine-2-carbaldiiminato), HL2 = N,N-dimethylethylene-N′-salicylaldiiminato, dca=dicyanamide anion] are described. Spectroscopic and electrochemical properties have also been discussed. A one-dimensional chain structure with single, symmetrical, μ1,5-dca bridges is found in compound 1. The copper atom in 1 has a square pyramidal geometry. A tridentate Schiff base ligand, having NNN donor sites, and one nitrogen atom from dca occupy the basal plane. N(18) of a neighbouring unit occupies the apical site. The Schiff base used in compound 2 is a tridentate anion with NNO donor sites, which changes the structure in a dinuclear unit of copper atoms bridged by single end-to-end dicyanamide ion. The environment around copper in 2 is square planar. Magnetic susceptibility measurements for 1 and 2 reveal the occurrence of weak antiferromagnetic interaction through the dca ligand. [Copyright &y& Elsevier]

Copper(II) complexes (1-3) of a sterically constrained phenol-based tetradentate N2O2 ligand 1,4-bis(2-hydroxy3,5-dimethylbenzyl)piperazine (H2L) have been reported. The associated anions of the copper(II) ion precursors have profound influence on the stoichiometry of the products. Thus, with perchlorate ion, the product is a binuclear compound [Cu2L2] (1), while with coordinating anions viz. CI- and N3-, the products [Cu3L2Cl2(H2O)]·1/2H2L (2) and [Cu3L2(N3)2(CH3OH)]·4H2O (3) have triangulo trinuclear composition. The syntheses, X-ray structures, and spectroscopic and magnetic properties of these complexes are described. Compound 1 has a noncentrosymmetric structure with a rectangular Cu2(OPh)2 core. It appears to be a rare example of a phenolato-bridged Cu(II) dimer exhibiting ferromagnetic interactions (J = 0.93 cm-1), a behavior in agreement with the theoretical predictions but seldom observed experimentally. In compounds 2 and 3, the copper centers are triangularly disposed, and the molecules have a shape much like that of a butterfly. The terminal copper centers Cu(1) and Cu(2) in 2 and 3 have distorted square pyramidal geometry, connected to each other by a bridging chloro- (in 2) or azido ligand (in 3) in "end to end" fashion. The central copper center (Cu(3) in 2 and Cu in 3) in both the compounds has distorted square planar geometry. The separations between the metal centers, viz. Cu(1)…(Cu(2), Cu(2)…Cu(3), and Cu(3)…Cu(1), are 4.826, 3.214, and 3.244 Å, respectively, in 2. The corresponding distances in 3 are 5.590, 3.178, and 3.485 Å, respectively. The overall magnetic behaviors in 2 and 3 are consistent with antiferromagnetic interactions between the spin centers. In 3, the exchange couplings between the terminal and central copper centers JCu(1)-Cu and JCu(2)-Cu appear to be equal (-234 cm-1), resulting in an S=½ ground state at temperatures near or below 77 K. [ABSTRACT FROM AUTHOR]