Thermal Spin Crossover and LIESST Effect Observed in Complexes [Fe(L^Ch)₂(NCX)₂] [L^Ch = 2,5-Di(2-Pyridyl)-1,3,4-Chalcadiazole; Ch = O, S, Se; X = S, Se, BH₃]

Two new complexes belonging to the family [Fe^II(<b>L</b>)₂(NCX)₂] have been synthesized and structurally characterized. Complexation of the ligand <b>L</b>^<b>O</b> = 2,5-di­(2-pyridyl)-1,3,4-oxadiazole results in the formation of two derivatives of [Fe^II(<b>L</b>^<b>O</b>)₂(NCS)₂] (<b>1</b>) with the common s-trans and the rarely observed s-cis conformation. No thermal spin crossover (SCO) was observed for the amorphous bulk material of the mixture. Using the new ligand <b>L</b>^<b>Se</b> = 2,5-di­(2-pyridyl)-1,3,4-selenadiazole, compound [Fe^II(<b>L</b>^<b>Se</b>)₂(NCS)₂]·1.4DCM·0.6MeOH (<b>2</b>·1.4DCM·0.6MeOH) was structurally characterized by single crystal X-ray diffraction. Bulk material of [Fe^II(<b>L</b>^<b>Se</b>)₂(NCS)₂]·MeOH (<b>2</b>·MeOH) exhibits a thermally induced SCO with small hysteresis [<i>T</i>_1/2(↓) = 91 K, <i>T</i>_1/2(↑) = 96 K]. LIESST and reflectivity studies have been performed on the SCO complexes [Fe^II(<b>L</b>^<b>S</b>)₂(NCS)₂], [Fe^II(<b>L</b>^<b>S</b>)₂(NCSe)₂], [Fe^II(<b>L</b>^<b>S</b>)₂(NCBH₃)₂]·H₂O [<b>L</b>^<b>S</b> = 2,5-di­(2-pyridyl)-1,3,4-thiadiazole], and <b>2</b>·MeOH. All complexes belong to the <i>T</i>₀ = 90 K line [<i>T</i>(LIESST) = <i>T</i>₀ – 0.3<i>T</i>_1/2]. [Fe^II(<b>L</b>^<b>S</b>)₂(NCS)₂], that exhibits a two-stepped thermal SCO process, has been found to also exhibit two well-separated <i>T</i>(LIESST) temperatures [<i>T</i>(LIESST, 1) = 44 K; <i>T</i>(LIESST, 2) = 53 K]

Thermal- and Light-Induced Spin-Crossover Bistability in a Disrupted Hofmann-Type 3D Framework

The expected 3D and 2D topologies resulting from combining approximately linear bis- or monopyridyl ligands with [Fe^IIM^II(CN)₄] (M^II = Pt, Pd, Ni) 4,4-grid sheets are well established. We show here the magnetic and structural consequences of incorporating a bent bispyridyl linker ligand in combination with [Fe^IIPt^II(CN)₄] to form the material [Fe­(H₂O)₂Fe­(DPSe)₂(Pt­(CN)₄)₂]·3EtOH (DPSe = 4,4′-dipyridylselenide). Structural investigations reveal an unusual connectivity loosely resembling a 3D Hofmann topology where (1) there are two distinct local iron­(II) environments, [Fe^IIN₆] (<b>Fe1</b>) and [Fe^IIN₄O₂] (<b>Fe2</b>), (2) as a consequence of axial water coordination to <b>Fe2</b>, there are “holes” in the [Fe^IIPt^II(CN)₄] 4,4 sheets because of some of the cyanido ligands being terminal rather than bridging, and (3) bridging of adjacent sheets occurs only through one in two DPSe ligands, with the other acting as a terminal ligand binding through only one pyridyl group. The magnetic properties are defined by this unusual topology such that only <b>Fe1</b> is in the appropriate environment for a high-spin to low-spin transition to occur. Magnetic susceptibility data reveal a complete and abrupt hysteretic spin transition (<i>T</i>_1/2↓ = 120 K and <i>T</i>_1/2↑ = 130 K) of this iron­(II) site; <b>Fe2</b> remains high-spin. This material additionally exhibits a photomagnetic response (uncommon for Hofmann-related materials), showing light-induced excited spin-state trapping [LIESST; <i>T</i>(LIESST) = 61 K] with associated bistability evidenced in a hysteresis loop (<i>T</i>_1/2↓ = 60 K and <i>T</i>_1/2↑ = 66 K)

Thermal- and Light-Induced Spin-Crossover Bistability in a Disrupted Hofmann-Type 3D Framework

The expected 3D and 2D topologies resulting from combining approximately linear bis- or monopyridyl ligands with [Fe^IIM^II(CN)₄] (M^II = Pt, Pd, Ni) 4,4-grid sheets are well established. We show here the magnetic and structural consequences of incorporating a bent bispyridyl linker ligand in combination with [Fe^IIPt^II(CN)₄] to form the material [Fe­(H₂O)₂Fe­(DPSe)₂(Pt­(CN)₄)₂]·3EtOH (DPSe = 4,4′-dipyridylselenide). Structural investigations reveal an unusual connectivity loosely resembling a 3D Hofmann topology where (1) there are two distinct local iron­(II) environments, [Fe^IIN₆] (<b>Fe1</b>) and [Fe^IIN₄O₂] (<b>Fe2</b>), (2) as a consequence of axial water coordination to <b>Fe2</b>, there are “holes” in the [Fe^IIPt^II(CN)₄] 4,4 sheets because of some of the cyanido ligands being terminal rather than bridging, and (3) bridging of adjacent sheets occurs only through one in two DPSe ligands, with the other acting as a terminal ligand binding through only one pyridyl group. The magnetic properties are defined by this unusual topology such that only <b>Fe1</b> is in the appropriate environment for a high-spin to low-spin transition to occur. Magnetic susceptibility data reveal a complete and abrupt hysteretic spin transition (<i>T</i>_1/2↓ = 120 K and <i>T</i>_1/2↑ = 130 K) of this iron­(II) site; <b>Fe2</b> remains high-spin. This material additionally exhibits a photomagnetic response (uncommon for Hofmann-related materials), showing light-induced excited spin-state trapping [LIESST; <i>T</i>(LIESST) = 61 K] with associated bistability evidenced in a hysteresis loop (<i>T</i>_1/2↓ = 60 K and <i>T</i>_1/2↑ = 66 K)

Thermal- and Light-Induced Spin-Crossover Bistability in a Disrupted Hofmann-Type 3D Framework

The expected 3D and 2D topologies resulting from combining approximately linear bis- or monopyridyl ligands with [Fe^IIM^II(CN)₄] (M^II = Pt, Pd, Ni) 4,4-grid sheets are well established. We show here the magnetic and structural consequences of incorporating a bent bispyridyl linker ligand in combination with [Fe^IIPt^II(CN)₄] to form the material [Fe­(H₂O)₂Fe­(DPSe)₂(Pt­(CN)₄)₂]·3EtOH (DPSe = 4,4′-dipyridylselenide). Structural investigations reveal an unusual connectivity loosely resembling a 3D Hofmann topology where (1) there are two distinct local iron­(II) environments, [Fe^IIN₆] (<b>Fe1</b>) and [Fe^IIN₄O₂] (<b>Fe2</b>), (2) as a consequence of axial water coordination to <b>Fe2</b>, there are “holes” in the [Fe^IIPt^II(CN)₄] 4,4 sheets because of some of the cyanido ligands being terminal rather than bridging, and (3) bridging of adjacent sheets occurs only through one in two DPSe ligands, with the other acting as a terminal ligand binding through only one pyridyl group. The magnetic properties are defined by this unusual topology such that only <b>Fe1</b> is in the appropriate environment for a high-spin to low-spin transition to occur. Magnetic susceptibility data reveal a complete and abrupt hysteretic spin transition (<i>T</i>_1/2↓ = 120 K and <i>T</i>_1/2↑ = 130 K) of this iron­(II) site; <b>Fe2</b> remains high-spin. This material additionally exhibits a photomagnetic response (uncommon for Hofmann-related materials), showing light-induced excited spin-state trapping [LIESST; <i>T</i>(LIESST) = 61 K] with associated bistability evidenced in a hysteresis loop (<i>T</i>_1/2↓ = 60 K and <i>T</i>_1/2↑ = 66 K)

Electronic Structure of a Spin Crossover Molecular Adsorbate

We have investigated the occupied and unoccupied electronic structure of ultrahigh vacuum (UHV) evaporated molecular thin films of the spin crossover [Fe­(H₂B­(pz)₂)₂(bipy)] complex (with H₂B­(pz)₂ = bis­(hydrido)­bis­(1<i>H</i>-pyrazol-1-yl)­borate and bipy = 2,2′-bipyridine) by ultraviolet photoelectron spectroscopy (UPS), inverse photoemission (IPES), and X-ray absorption spectroscopy (XAS). A bandgap of 2–3 eV is deduced from combined UPS and IPES measurements of the molecular films on Au substrates. The matching Fe XAS and IPES spectra indicate that the electronic unoccupied states have a significant Fe weight. The shift of the unoccupied density of states seen in inverse photoemission is consistent with the thermally induced spin crossover transition for [Fe­(H₂B­(pz)₂)₂(bipy)] deposited on the organic ferroelectric copolymer poly­(vinylidene fluoride) with trifluoroethylene (PVDF–TrFE)

Comparison of the performance of Skin Prick, ImmunoCAP, and ISAC tests in the diagnosis of patients with allergy

Background: Allergy is diagnosed from typical symptoms, and tests are performed to incriminate the suspected precipitant. Skin prick tests (SPTs) are commonly performed, inexpensive, and give immediate results. Laboratory tests (ImmunoCAP) for serum allergen-specific IgE antibodies are usually performed more selectively. The immuno-solid phase allergen chip (ISAC) enables testing for specific IgE against multiple allergen components in a multiplex assay. Methods: We retrospectively analysed clinic letters, case notes, and laboratory results of 118 patients attending the National Adult Allergy Service at the University Hospital of Wales who presented diagnostic difficulty, to evaluate which testing strategy (SPT, ImmunoCAP, or ISAC) was the most appropriate to use to confirm the diagnosis in these complex patients, evaluated in a “real-life” clinical service setting. Results: In patients with nut allergy, the detection rates of SPTs (56%) and ISAC (65%) were lower than those of ImmunoCAP (71%). ISAC had a higher detection rate (88%) than ImmunoCAP (69%) or SPT (33%) in the diagnosis of oral allergy syndrome. ImmunoCAP test results identified all 9 patients with anaphylaxis due to wheat allergy (100%), whereas ISAC was positive in only 6 of these 9 (67%). Conclusions: In this difficult diagnostic group, the ImmunoCAP test should be the preferred single test for possible allergy to nuts, wheat, other specific foods, and anaphylaxis of any cause. In these conditions, SPT and ISAC tests give comparable results. The most useful single test for oral allergy syndrome is ISAC, and SPT should be the preferred test for latex allergy

Stimuli Responsive Hybrid Magnets: Tuning the Photoinduced Spin-Crossover in Fe(III) Complexes Inserted into Layered Magnets

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 [Fe^III(sal₂-trien)]­[Mn^IICr^III(ox)₃]·CHCl₃ (<b>1·CHCl</b>_<b>3</b>), [Fe^III(sal₂-trien)]­[Mn^IICr^III(ox)₃]·CHBr₃ (<b>1·CHBr</b>_<b>3</b>), and [Fe^III(sal₂-trien)]­[Mn^IICr^III(ox)₃]·CH₂Br₂ (<b>1·CH</b>_<b>2</b><b>Br</b>_<b>2</b>). The three compounds crystallize in a 2D honeycomb anionic layer formed by Mn^II and Cr^III 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 <i>T</i>_1/2. The three compounds present a LIESST effect with a relaxation temperature <i>T</i>_LIESST inversely proportional to <i>T</i>_1/2. The isostructural paramagnetic compound, [Fe^III(sal₂-trien)]­[Zn^IICr^III(ox)₃]·CH₂Cl₂ (<b>2·CH</b>_<b>2</b><b>Cl</b>_<b>2</b>) was also prepared. This compound presents a partial spin crossover of the inserted Fe^III complex as well as a LIESST effect. Finally, spectroscopic characterization of the Fe^III doped compound [Ga_0.99Fe_0.01(sal₂trien)]­[Mn^IICr^III(ox)₃]·CH₂Cl₂ (<b>3·CH</b>_<b>2</b><b>Cl</b>_<b>2</b>) shows a gradual and complete thermal spin crossover and a LIESST effect on the isolated Fe^III complexes. This result confirms that cooperativity is not a necessary condition to observe the LIESST effect in an Fe^III compound

Stimuli Responsive Hybrid Magnets: Tuning the Photoinduced Spin-Crossover in Fe(III) Complexes Inserted into Layered Magnets

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 [Fe^III(sal₂-trien)]­[Mn^IICr^III(ox)₃]·CHCl₃ (<b>1·CHCl</b>_<b>3</b>), [Fe^III(sal₂-trien)]­[Mn^IICr^III(ox)₃]·CHBr₃ (<b>1·CHBr</b>_<b>3</b>), and [Fe^III(sal₂-trien)]­[Mn^IICr^III(ox)₃]·CH₂Br₂ (<b>1·CH</b>_<b>2</b><b>Br</b>_<b>2</b>). The three compounds crystallize in a 2D honeycomb anionic layer formed by Mn^II and Cr^III 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 <i>T</i>_1/2. The three compounds present a LIESST effect with a relaxation temperature <i>T</i>_LIESST inversely proportional to <i>T</i>_1/2. The isostructural paramagnetic compound, [Fe^III(sal₂-trien)]­[Zn^IICr^III(ox)₃]·CH₂Cl₂ (<b>2·CH</b>_<b>2</b><b>Cl</b>_<b>2</b>) was also prepared. This compound presents a partial spin crossover of the inserted Fe^III complex as well as a LIESST effect. Finally, spectroscopic characterization of the Fe^III doped compound [Ga_0.99Fe_0.01(sal₂trien)]­[Mn^IICr^III(ox)₃]·CH₂Cl₂ (<b>3·CH</b>_<b>2</b><b>Cl</b>_<b>2</b>) shows a gradual and complete thermal spin crossover and a LIESST effect on the isolated Fe^III complexes. This result confirms that cooperativity is not a necessary condition to observe the LIESST effect in an Fe^III compound

Stimuli Responsive Hybrid Magnets: Tuning the Photoinduced Spin-Crossover in Fe(III) Complexes Inserted into Layered Magnets

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 [Fe^III(sal₂-trien)]­[Mn^IICr^III(ox)₃]·CHCl₃ (<b>1·CHCl</b>_<b>3</b>), [Fe^III(sal₂-trien)]­[Mn^IICr^III(ox)₃]·CHBr₃ (<b>1·CHBr</b>_<b>3</b>), and [Fe^III(sal₂-trien)]­[Mn^IICr^III(ox)₃]·CH₂Br₂ (<b>1·CH</b>_<b>2</b><b>Br</b>_<b>2</b>). The three compounds crystallize in a 2D honeycomb anionic layer formed by Mn^II and Cr^III 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 <i>T</i>_1/2. The three compounds present a LIESST effect with a relaxation temperature <i>T</i>_LIESST inversely proportional to <i>T</i>_1/2. The isostructural paramagnetic compound, [Fe^III(sal₂-trien)]­[Zn^IICr^III(ox)₃]·CH₂Cl₂ (<b>2·CH</b>_<b>2</b><b>Cl</b>_<b>2</b>) was also prepared. This compound presents a partial spin crossover of the inserted Fe^III complex as well as a LIESST effect. Finally, spectroscopic characterization of the Fe^III doped compound [Ga_0.99Fe_0.01(sal₂trien)]­[Mn^IICr^III(ox)₃]·CH₂Cl₂ (<b>3·CH</b>_<b>2</b><b>Cl</b>_<b>2</b>) shows a gradual and complete thermal spin crossover and a LIESST effect on the isolated Fe^III complexes. This result confirms that cooperativity is not a necessary condition to observe the LIESST effect in an Fe^III compound

Stimuli Responsive Hybrid Magnets: Tuning the Photoinduced Spin-Crossover in Fe(III) Complexes Inserted into Layered Magnets

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 [Fe^III(sal₂-trien)]­[Mn^IICr^III(ox)₃]·CHCl₃ (<b>1·CHCl</b>_<b>3</b>), [Fe^III(sal₂-trien)]­[Mn^IICr^III(ox)₃]·CHBr₃ (<b>1·CHBr</b>_<b>3</b>), and [Fe^III(sal₂-trien)]­[Mn^IICr^III(ox)₃]·CH₂Br₂ (<b>1·CH</b>_<b>2</b><b>Br</b>_<b>2</b>). The three compounds crystallize in a 2D honeycomb anionic layer formed by Mn^II and Cr^III 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 <i>T</i>_1/2. The three compounds present a LIESST effect with a relaxation temperature <i>T</i>_LIESST inversely proportional to <i>T</i>_1/2. The isostructural paramagnetic compound, [Fe^III(sal₂-trien)]­[Zn^IICr^III(ox)₃]·CH₂Cl₂ (<b>2·CH</b>_<b>2</b><b>Cl</b>_<b>2</b>) was also prepared. This compound presents a partial spin crossover of the inserted Fe^III complex as well as a LIESST effect. Finally, spectroscopic characterization of the Fe^III doped compound [Ga_0.99Fe_0.01(sal₂trien)]­[Mn^IICr^III(ox)₃]·CH₂Cl₂ (<b>3·CH</b>_<b>2</b><b>Cl</b>_<b>2</b>) shows a gradual and complete thermal spin crossover and a LIESST effect on the isolated Fe^III complexes. This result confirms that cooperativity is not a necessary condition to observe the LIESST effect in an Fe^III compound