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1.
Artigo em Inglês | MEDLINE | ID: mdl-32358911

RESUMO

Domain wall motion is detected for the first time during the transition to a ferroelastic and spin state ordered phase of a spin crossover complex. Single-crystal X-ray diffraction and resonant ultrasound spectroscopy (RUS) revealed two distinct symmetry-breaking phase transitions in the mononuclear Mn3+ compound [Mn(3,5-diBr-sal2 (323))]BPh4 , 1. The first at 250 K, involves the space group change Cc→Pc and is thermodynamically continuous, while the second, Pc→P1 at 85 K, is discontinuous and related to spin crossover and spin state ordering. Stress-induced domain wall mobility was interpreted on the basis of a steep increase in acoustic loss immediately below the the Pc-P1 transition.

2.
J Am Chem Soc ; 142(2): 931-936, 2020 Jan 15.
Artigo em Inglês | MEDLINE | ID: mdl-31880442

RESUMO

A one-dimensional coordination solid 1c is synthesized by reaction of a bispyridyl dithienylethene (DTE) photochromic unit with the highly anisotropic dysprosium-based single-molecule magnet [Dy(Tppy)F(pyridine)2]PF6. Slow magnetic relaxation characteristics are retained in the chain compound 1c, and photoisomerization of the bridging DTE ligand induces a single-crystal-to-single-crystal transformation that can be monitored using photocrystallography. Notably, the resulting chain compound 1o exhibits faster low-temperature relaxation than that of 1c, which is apparent in magnetic hysteresis data collected for both compounds as high as 4 K. Ab initio calculations suggest that this photomodulation of the magnetic relaxation behavior is due to crystal packing changes rather than changes to the crystal field splitting upon ligand isomerization.

3.
Angew Chem Int Ed Engl ; 58(34): 11811-11815, 2019 Aug 19.
Artigo em Inglês | MEDLINE | ID: mdl-31233272

RESUMO

Molecular magnetic switches are expected to form the functional components of future nanodevices. Herein we combine detailed (photo-) crystallography and magnetic studies to reveal the unusual switching properties of an iron(III) complex, between low (LS) and high (HS) spin states. On cooling, it exhibits a partial thermal conversion associated with a reconstructive phase transition from a [HS-HS] to a [LS-HS] phase with a hysteresis of 25 K. Photoexcitation at low temperature allows access to a [LS-LS] phase, never observed at thermal equilibrium. As well as reporting the first iron(III) spin crossover complex to exhibit reverse-LIESST (light-induced excited spin state trapping), we also reveal a hidden hysteresis of 30 K between the hidden [LS-LS] and [HS-LS] phases. Moreover, we demonstrate that FeIII spin-crossover (SCO) complexes can be just as effective as FeII systems, and with the advantage of being air-stable, they are ideally suited for use in molecular electronics.

4.
Inorg Chem ; 57(16): 9880-9891, 2018 Aug 20.
Artigo em Inglês | MEDLINE | ID: mdl-30080034

RESUMO

A series of bulky substituted bipyridine-related iron(II) complexes [Fe(H2Bpz2)2(L)] (pz = pyrazolyl) were prepared, where L = 5,5'-dimethyl-2,2'-bipyridine (bipy-CH3, 1), L = dimethyl-2,2'-bipyridyl-5,5'-dicarboxylate (MeObpydc, 2), L = diethyl-2,2'-bipyridyl-5,5'-dicarboxylate (EtObpydc, 3), or L = diisopropyl-2,2'-bipyridine-5,5'-dicarboxylate ( i-PrObpydc, 4). The crystal structures of five new iron(II) complexes were determined by X-ray diffraction: those of 1, 3, and 4 and two modifications of 3 (3B) and 4 (4B). Complexes 1 and 3B display incomplete spin crossover (SCO) behavior because of a freezing-in effect, whereas 3 and 4B undergo gradual and incomplete SCO behaviors. Complexes 2 and 4 show a completely gradual and steep SCO, respectively. Such different SCO behaviors can be attributed to an electronic substituent effect in the bipyridyl ligand conformation and a crystal packing effect. Importantly, the electronic substituent effect of the isopropyl acetate group and C-H···O supramolecular interactions in 4 contribute to a highly cooperative behavior, which leads to an abrupt thermally induced spin transition.

5.
Chem Sci ; 9(25): 5623-5629, 2018 Jul 07.
Artigo em Inglês | MEDLINE | ID: mdl-30061995

RESUMO

Molecule-based spin state switching materials that display ambient temperature transitions with accompanying wide thermal hysteresis offer an opportunity for electronic switching, data storage, and optical technologies but are rare in existence. Here, we present the first 2D Hofmann-type materials to exhibit the elusive combination of ambient temperature spin crossover with wide thermal hysteresis (ΔT = 50 and 65 K). Combined structural, magnetic, spectroscopic, and theoretical analyses show that the highly cooperative transition behaviours of these layered materials arise due to strong host-host interactions in their interdigitated lattices, which optimises long-range communication pathways. With the presence of water molecules in the interlayer pore space in the hydrated phases, competing host-host and host-guest interactions occur, whilst water removal dramatically increases the framework cooperativity, thus affording systematic insight into the structural features that favour optimal spin crossover properties.

6.
Chemistry ; 24(55): 14760-14767, 2018 Oct 01.
Artigo em Inglês | MEDLINE | ID: mdl-29985534

RESUMO

Spin-transition compounds are coordination complexes that can present two stable or metastable high-spin and low-spin states at a given temperature (thermal hysteresis). The width of the thermal hysteresis (difference between the maximum and minimum temperature between which the compound exhibits bi-stability) depends on the interactions between the coordination complexes within the compound, and which may be modulated by the absence or presence of solvent within the structure. The new compound [Fe(3-bpp)2 ][Au(CN)2 ]2 (1, 3-bpp=2,6-di-(1H-pyrazol-3-yl)pyridine) was synthesized and its properties were compared with those of the solvated compound [Fe(3-bpp)2 ][Au(CN)2 ]2 ⋅2 H2 O (1.H2 O) already described. 1 has a two-steps thermal hysteresis of 45 K, in contrast to the compound 1.H2 O which exhibits a gradual conversion without hysteresis. This hysteretic transition is accompanied by a reversible reconstructive structural transition and twinning. This stepped behaviour is also observed in the photomagnetic properties despite the low efficiency of photoswitching. Single-crystal photocrystallographic investigations confirm this low conversion, which we attributed to the high energy cost to form the high-spin structure, whose symmetry differs from that of the low-spin phase.

7.
IUCrJ ; 5(Pt 3): 361-372, 2018 May 01.
Artigo em Inglês | MEDLINE | ID: mdl-29755752

RESUMO

A mixed-valence conducting cation radical salt of the unsymmetrically substituted o-Me2TTF donor molecule (TTF is tetrathiafulvalene) was obtained upon electrocrystallization in the presence of the non-centrosymmetric NO3- anion. It crystallizes at room temperature in the monoclinic P21/c space group, with the anion disordered on an inversion centre. The donor molecules are stacked along the a axis. A 90° rotation of the longest molecular axis of o-Me2TTF generates a chessboard-like structure, preventing lateral S⋯S contacts between stacks and providing a strongly one-dimensional electronic system, as confirmed by overlap interaction energies and band structure calculations. A strong dimerization within the stacks explains the semi-conducting behaviour of the salt, with σroom temp = 3-5 S cm-1 and Eactivated = 0.12-0.14 eV. An X-ray diffuse scattering survey of reciprocal space, combined with full structure resolutions at low temperatures (250, 85 and 20 K), evidenced the succession of two structural transitions: a ferroelastic one with an anion-ordering (AO) process and the establishment of a (0, ½, ½) superstructure below 124 (±3) K, also visible via resistivity thermal dependence, followed by a stack tetramerization with the establishment of a (½, ½, ½) superstructure below 90 (±5) K. The latter ground state is driven by a spin-Peierls (SP) instability, as demonstrated by the temperature dependence of the magnetic susceptibility. Surprisingly, these two kinds of instability appear to be fully decoupled here, at variance with other tetra-methyl-tetra-thia-fulvalene (TMTTF) or tetramethyl-tetra-selena-fulvalene (TMTSF) salts with such non-centrosymmetric counter-ions.

8.
Chem Commun (Camb) ; 53(99): 13268-13271, 2017 Dec 12.
Artigo em Inglês | MEDLINE | ID: mdl-29186217

RESUMO

Light-Induced Excited Spin State Trapping (LIESST) data are reported for seven isostructural solvate salts from the iron(ii)/2,6-di(pyrazol-1-yl)pyridine family. A complicated relationship between their spin-crossover T1/2 and T(LIESST) values may reflect low-temperature thermal and light-induced symmetry breaking, which is shown by one of the compounds but not by two others.

9.
Chem Commun (Camb) ; 53(74): 10283-10286, 2017 Sep 14.
Artigo em Inglês | MEDLINE | ID: mdl-28868544

RESUMO

The organization of a molecular FeIII complex embedded in a halogen-bonded 2D network is chemically tuned to trigger temperature- and light-induced spin-state switching. We attribute the associated magnetic properties and the unprecedented photoswitching effect to the optimized structural confinement provided by the presence of the supramolecular host framework.

10.
Acta Crystallogr B Struct Sci Cryst Eng Mater ; 73(Pt 4): 660-668, 2017 Aug 01.
Artigo em Inglês | MEDLINE | ID: mdl-28762976

RESUMO

The complex relaxation from the photoinduced high-spin phase (PIHS) to the low-spin phase of the bimetallic two-dimensional coordination spin-crossover polymer [Fe[(Hg(SCN)3)2](4,4'-bipy)2]n is reported. During the thermal relaxation, commensurate and incommensurate spin-state concentration waves (SSCWs) form. However, contrary to the steps forming at thermal equilibrium, associated with long-range SSCW order, the SSCWs forming during the relaxation from the PIHS phase correspond to short-range order, revealed by diffuse X-ray scattering. This is interpreted as resulting from the competition between the two types of SSCW order and another structural symmetry breaking, due to ligand ordering, occurring at low temperature and precluding long-range SSCW order.

11.
Chem Asian J ; 12(12): 1338-1346, 2017 Jun 19.
Artigo em Inglês | MEDLINE | ID: mdl-28407369

RESUMO

The reactivity of functionalized ynamides and arylynamines with tetracyanoethylene at room temperature was evaluated. In most cases, the corresponding 1,1,4,4-tetracyanobutadienes (TCBDs) were obtained in good to excellent yields through a [2+2]-cycloaddition/[2+2]-retro-electrocyclization sequence. The influence of diverse functional groups on the yield of the reaction was investigated, in particular concerning multiple ynamides. These TCBDs were characterized by various spectroscopic techniques and electrochemistry and X-ray diffraction in some cases.

12.
Angew Chem Int Ed Engl ; 55(30): 8675-9, 2016 07 18.
Artigo em Inglês | MEDLINE | ID: mdl-27193972

RESUMO

The unprecedented bimetallic 2D coordination polymer {Fe[(Hg(SCN)3 )2 ](4,4'-bipy)2 }n exhibits a thermal high-spin (HS)↔low-spin (LS) staircase-like conversion characterized by a multi-step dependence of the HS molar fraction γHS . Between the fully HS (γHS =1) and LS (γHS =0) phases, two steps associated with different ordering appear in terms of spin-state concentration waves (SSCW). On the γHS ≈0.5 step, a periodic SSCW forms with a HS-LS-HS-LS sequence. On the γHS ≈0.34 step, the 4D superspace crystallography structural refinement reveals an aperiodic SSCW, with a HS-LS sequence incommensurate with the molecular lattice. The formation of these different long-range spatially ordered structures of LS and HS states during the multi-step spin-crossover is discussed within the framework of "Devil's staircase"-type transitions. Spatially modulated phases are known in various types of materials but are uniquely related to molecular HS/LS bistability in this case.

14.
Chemistry ; 22(13): 4634-6, 2016 03 18.
Artigo em Inglês | MEDLINE | ID: mdl-26928979

RESUMO

A summary of the evidence based on spectroscopy, calculated density of states (DOS) and photo-electrochemistry, for electron transfer from the occupied Fe(2+) (d)-ß orbital located within the band gap of the [Ti4 O(OEt)15 (FeBr)] cluster, to its unoccupied Ti(d) orbitals is presented. The importance of the distinction between the concepts of band gap and HOMO-LUMO gap is emphasized.

15.
Chem Commun (Camb) ; 51(99): 17630, 2015 Dec 25.
Artigo em Inglês | MEDLINE | ID: mdl-26593385

RESUMO

Correction for 'Electronic vs. structural ordering in a manganese(III) spin crossover complex' by Anthony J. Fitzpatrick et al., Chem. Commun., 2015, DOI: 10.1039/c5cc05129k.

16.
Chem Commun (Camb) ; 51(99): 17540-3, 2015 Dec 25.
Artigo em Inglês | MEDLINE | ID: mdl-26501138

RESUMO

A symmetry breaking spin transition in a Mn(III) complex is reported with three structural phases, a high symmetry high temperature S = 2 phase, an intermediate S = 1/S = 2 ordered phase and an aperiodic low temperature phase with S = 1 cations. The aperiodicity is interpreted as resulting from long-range ordering of the NTf2(-) anions.

17.
Chemistry ; 21(32): 11538-44, 2015 Aug 03.
Artigo em Inglês | MEDLINE | ID: mdl-26147327

RESUMO

Homodisperse doped polyoxotitanate nanoclusters with formulae Ti11 (MX)O14 (OiPr)17 (M=Mn, Fe or Co; X=Cl, Br or I, OiPr=isopropoxide) display strongly dopant-dependent properties. Spectroscopic solution and reflectance measurements backed up by density of states and time-dependent DFT calculations based on the determined structures, show the prominent effect of FeX substitution by decreasing the HOMO-LUMO gap of the particles. The effect is attributed to the presence of an occupied Fe ß orbital halfway up the bandgap, leading to long-wavelength absorption with electron transfer to the titanium atoms of the cluster. Whereas the light absorption varies significantly with variation of the transition metal dopant, its dependency on the nature of the halogen atom or the change in dipole moment across the series is minor.

18.
Inorg Chem ; 53(19): 10594-601, 2014 Oct 06.
Artigo em Inglês | MEDLINE | ID: mdl-25238405

RESUMO

The triplet excited state of a new crystalline form of a tetranuclear coordination d(10)-d(10)-type complex, Ag2Cu2L4 (L = 2-diphenylphosphino-3-methylindole ligand), containing Ag(I) and Cu(I) metal centers has been explored using the Laue pump-probe technique with ≈80 ps time resolution. The relatively short lifetime of 1 µs is accompanied by significant photoinduced structural changes, as large as the Ag1···Cu2 distance shortening by 0.59(3) Å. The results show a pronounced strengthening of the argentophilic interactions and formation of new Ag···Cu bonds on excitation. Theoretical calculations indicate that the structural changes are due to a ligand-to-metal charge transfer (LMCT) strengthening the Ag···Ag interaction, mainly occurring from the methylindole ligands to the silver metal centers. QM/MM optimizations of the ground and excited states of the complex support the experimental results. Comparison with isolated molecule optimizations demonstrates the restricting effect of the crystalline matrix on photoinduced distortions. The work represents the first time-resolved Laue diffraction study of a heteronuclear coordination complex and provides new information on the nature of photoresponse of coinage metal complexes, which have been the subject of extensive studies.


Assuntos
Cobre/química , Luz , Substâncias Luminescentes/química , Compostos Organometálicos/química , Prata/química , Processos Fotoquímicos , Teoria Quântica , Fatores de Tempo
19.
Phys Chem Chem Phys ; 16(30): 15792-5, 2014 Aug 14.
Artigo em Inglês | MEDLINE | ID: mdl-24964263

RESUMO

Whereas a large number of sensitized polyoxotitanate clusters have been reported, information on the electrochemical properties of the fully structurally defined nanoparticles is not available. Bridging of this gap will allow a systematic analysis of the relation between sensitizer-cluster binding geometry, electronic structure and electron injection properties. Ti17O28(O(i)Pr)16(Fe(II)Phen)2 is a member of a doubly-doped series of nanoclusters in which the phenanthroline is attached to the surface-located transition metal atom. The visible spectrum of a dichloromethane solution of the studied sample shows a series of absorption bands in the 400-900 nm region. Theoretical DOS and TDDFT calculations indicate that the bands in increasing wavelength order correspond essentially to metal-to-core charge transfer (MCCT) at ∼460 nm, metal-to-ligand charge transfer (MLCT) at ∼520 nm and d-d metal-atom transitions. Exposure of a thin layer of the sample to light in a photoelectrochemical cell produces an electric current in the 400 to ∼640 nm region. The fit of the wavelength range of the electron injection with the results of the calculations suggests that charge injection into the FTO anode occurs both from the TiO cluster and from the phenanthroline ligand. Injection from the phenanthroline via the cluster orbitals is ruled out by the lower energy of the phenanthroline orbitals.

20.
Chem Rev ; 114(19): 9645-61, 2014 Oct 08.
Artigo em Inglês | MEDLINE | ID: mdl-24820889
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