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Herein, we report a twisted cubic Cu(I)4Ti(IV)4-oxo cluster stabilized by in situ – formed 2,2′-biphenolate ligands from the oxidative coupling of phenols. The 2,2′-biphenolate-functionalized Cu(I)4Ti(IV)4O4 cluster shows short Cu⋯C contacts and exhibits smaller HOMO–LUMO gaps than those of reported Ti(IV)4O4. [ABSTRACT FROM AUTHOR]

Spin-crossover (SCO) materials have been extensively investigated in the past few decades with promising applications in a wide range of fields including displays, sensors, and storage components. The introduction of secondary physical properties to SCO materials resulting in bifunctional materials is becoming a research hot spot. In particular, for the fluorescent SCO materials, fluorescence can serve as a sensitive probe that easily expresses the spin-state changes of SCO materials; therefore, fluorescent SCO bifunctional materials have promising applications in the fields of magneto-optical switching and information processing. In this perspective, we briefly review the main synthetic strategies and progresses in fluorescent SCO materials in the last twenty years. [ABSTRACT FROM AUTHOR]

A series of dynamic single crystals with a chemical formula of [MII(en)3]SO4 (en = ethylene and MII = NiII, MnII, and CdII) was synthesized. As the temperature decreases, these materials exhibit dielectric switching in the vicinity of the phase transition point accompanied by anisotropic thermal expansion in the cell parameters as a consequence of the order–disorder structural change of SO 2−4 in a cavity surrounded by five [MII(en)3]2+ complex cations. Because the variation of metal centers with different ionic radii changes the shape of the complex cation, which affects the distribution of hydrogen-bond interactions around the SO 2−4 , the dynamic motion of SO 2−4 is substantially tuned. Correspondingly, the dielectric properties and anisotropic thermal expansion of materials were largely shifted, especially in the single crystals of [MnII(en)3]SO4, whose structural change is distinctly different from the crystals of Ni(II) and Cd(II). The detailed structural mechanism accounting for the different physical properties of these materials was discussed. [ABSTRACT FROM AUTHOR]

A mononuclear complex with long alkyl chains, [FeII(H2Bpz2)2(C9bpy)] (1; H2Bpz2 = dihydrobis(1-pyrazolyl)borate, C9bpy = 4,4′-dinonyl-2,2′-bipyridine), was synthesized. Single-crystal X-ray crystallographic studies revealed that the Δ- and Λ-forms of the complex co-crystallized in the lattice asymmetric unit, while magnetic measurements unveiled that this complex underwent incomplete one-step spin crossover (SCO) with the transition completeness and temperature depending on the measurement velocity because of slow spin equilibrium. Multivariable approaches such as varying scan rate, annealing the sample, light irradiation and pressure have been adopted to effectively overcome the slow spin equilibrium and thus improve the SCO completeness. [ABSTRACT FROM AUTHOR]

Hofmann-type spin-crossover (SCO) frameworks attract much attention due to their predictable structures and diverse SCO behaviours. In this paper, we report two isostructural two-dimensional (2D) Hofmann-type SCO frameworks [FeII(ppe)2MII(CN)4]·3H2O (ppe = 1-(2-pyridyl)-2-(4-pyridyl)ethylene and M = Pd for 1 and Pt for 2). X-ray crystallographic studies, magnetic measurements and Mössbauer spectra jointly reveal that both compounds undergo complete hysteretic two-step SCO, i.e. HS1.0 HS0.6–0.5LS0.4–0.5 LS1.0 conversion with thermal hysteresis loops of 14 K and 28 K wide for 1 and 13 K and 26 K wide for 2. The dehydrated samples, 1-dehydrated and 2-dehydrated, display different SCO behaviours, unveiling that the SCO behaviours are affected by guest water molecules. [ABSTRACT FROM AUTHOR]

Reversible single crystal-to-single crystal transformations from [FeL2(NCS)2]·3MeOH (1·3MeOH, L = 2-(anthracen-10-yl)-1H-imidazo[4,5-f][1,10]phenanthroline) to 1 and 1·2H2O were reported, which were accompanied by on–off switching of the spin-crossover properties. [ABSTRACT FROM AUTHOR]

Three one-dimensional looped coordination polymers with the formula of [Fe(dpds)2{C(CN)3}2]·dpds (1, dpds = 4,4′-dipyridyl disulfide), [Fe(dpds)2(NCBH3)2] (2) and [Fe(dpds)2(NCSe)2]·3.5H2O (3) have been synthesized and characterized by single-crystal X-ray crystallography, Mössbauer spectroscopy and magnetic measurements. The spin-crossover (SCO) behaviors of these compounds depend significantly on axial ligands: compound 1 exhibited thermal-induced complete one-step SCO behavior with a T1/2 of 170 K, and 2 showed incomplete SCO behavior with T1/2 being 130 K, whereas 3 was paramagnetic. Meanwhile, both compounds 1 and 2 displayed light-induced excited spin-state trapping (LIESST) effects, featuring TLIESST values of 45 K and 61 K for 1 and 2, respectively, which were independent of exciting laser wavelengths. These results suggest that anions such as C(CN)3− and NCBH3− with much stronger ligand fields are needed in order to realize spin-state switching, if a ligand such as dpds is adopted to synthesize SCO compounds. [ABSTRACT FROM AUTHOR]

Six analogous dumbbell-shaped 3d–4f complexes MII5LnIII4 were obtained by the reaction of Ln(NO3)3 (Ln = Eu, Gd, Dy) and M(OAc)2 (M = Co, Ni) without any other organic ligands, and M5Gd4 exhibited a large magnetocaloric effect (−ΔSm = 31.0, 37.3 J kg−1 K−1 for Co5Gd4 and Ni5Gd4 respectively), while M5Dy4 and Co5Eu4 showed single molecule magnet behaviour. To the best of our knowledge, Co5Eu4 is the first Eu-based cluster to display single molecule magnet behaviour (Ueff = 16.4 K). [ABSTRACT FROM AUTHOR]

A novel bent ligand-pillared three-dimensional Hofmann-type metal–organic framework, [FeII(Hbpt)Pt(CN)4]·1/2Hbpt·1/2CH3OH·5/2H2O [1, Hbpt = 4,4′-(1H-1,2,4-triazole-3,5-diyl) dipyridine], was synthesized and crystallographically and magnetically characterized, which showed incomplete three-step spin-crossover behavior with a reversible three equal-step sequence of HS1.00↑ HS0.75LS0.25↑ HS0.5LS0.5↑ HS0.25LS0.75. [ABSTRACT FROM AUTHOR]

The reactions of tricyanometallate precursors, (Ph3PMe)[(Tp4-Me)Fe(CN)3·0.5CH3CN] (1) (Tp4-Me = tri(4-methyl-pyrazol-1-yl)borate) and (NBu4)[(MeTp)Fe(CN)3] (MeTp = methyltris(pyrazolyl)borate) with the presence of the tetradentate tpa ligand (tpa = tris(2-pyridylmethyl)amine) and Fe(ClO4)2·6H2O afford two new cyano-bridged mixed-valence {FeIII2FeII2} molecular squares: [(Tp4-Me)FeIII(CN)3]2[FeII(tpa)]2·2ClO4·H2O (2·H2O) and [(MeTp)FeIII(CN)3]2[FeII(tpa)]2·2ClO4·CH3OH (3·CH3OH). Solvent-exchange compounds of 3·CH3OH, [(MeTp)FeIII(CN)3]2[FeII(tpa)]2·2ClO4·2H2O (3·2H2O), and their solvent-free form (2 and 3) are also obtained, respectively. The spin crossover (SCO) properties of all compounds are confirmed by detailed structural analyses of the coordination environments of the FeII centres and magnetic susceptibility measurements. All compounds exhibit SCO behaviour near room temperature (T1/2 = 320 K for 2·H2O; 302 K for 2; 292 K for 3·CH3OH; 306 K for 3·2H2O and 290 K for 3) and reversible single-crystal to single-crystal (SC–SC) transformations induced by guest desorption and resorption or solvent exchange. The transition temperature close to room temperature can be tuned by the dehydration and re-hydration processes. The structure–property analysis discloses that the distorted {Fe4(μ-CN)4} core and deviations of bent 〈Fe−N≡C angles play a key role in tuning the transition temperature of these similar mixed-valence {FeIII2FeII2} complexes. [ABSTRACT FROM AUTHOR]

A novel cobalt compound [Co9(HL)4(L)4Cl2]·(EtOH)2(H2O)2(H3L= (E)-2-2((1,3-dihydroxy-2-methylpropan-2-ylimino)methyl) phenol) has been solvothermally synthesized and structurally characterized. The compound crystallised in the space group C2/cwith a= 32.624(2) Å, b= 9.4814(4) Å, c= 33.395(2) Å, β= 109.339(5)° and V= 9746.8(9) Å3. The crystal structure is a mixed-valence nonanuclear Co(II/III) oligomer, which contains a square-pyramidal CoII5core formed through μ4-Cl and μ3-alkoxo bridges and the pentanuclear CoII5core is surrounded by four peripheral Co(III) ions at the square-pyramidal base plane through μ2-alkoxo bridges. Magnetic properties of the compound can be considered as the magnetism of the CoII5core, and the superexchange interactions between Co(II) ions within the core were calculated with three Co(II)–Co(II) superexchange parameters by using MAGPACK software package to give J1= + 11.1 cm−1, J2= −6.50 cm−1, J3= −3.25 cm−1, D= + 6.0 cm−1and g= 2.30. [ABSTRACT FROM AUTHOR]