The reactions of tricyanometallate precursors, (PhPMe)[(Tp)Fe(CN)·0.5CHCN] (1) (Tp = tri(4-methyl-pyrazol-1-yl)borate) and (NBu)[(Tp)Fe(CN)] (Tp = methyltris(pyrazolyl)borate) with the presence of the tetradentate tpa ligand (tpa = tris(2-pyridylmethyl)amine) and Fe(ClO)·6HO afford two new cyano-bridged mixed-valence {FeFe} molecular squares: [(Tp)Fe(CN)][Fe(tpa)]·2ClO·HO (2·HO) and [(Tp)Fe(CN)][Fe(tpa)]·2ClO·CHOH (3·CHOH). Solvent-exchange compounds of 3·CHOH, [(Tp)Fe(CN)][Fe(tpa)]·2ClO·2HO (3·2HO), 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 Fe centres and magnetic susceptibility measurements. All compounds exhibit SCO behaviour near room temperature (T = 320 K for 2·HO; 302 K for 2; 292 K for 3·CHOH; 306 K for 3·2HO 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 {Fe(μ-CN)} core and deviations of bent ∠Fe-N[triple bond, length as m-dash]C angles play a key role in tuning the transition temperature of these similar mixed-valence {FeFe} complexes.

Two new cyano-bridged mixed-valence {Fe III 2 (μ-CN) 4 Fe II 2 } clusters, {[(Tp)Fe III. Complexes 1 and 2•5MeOH exhibit gradual thermally induced two-step spin-crossover behavior (SCO) at two Fe II metal centers, and the transformation of high-spin (HS) to low-spin (LS) Fe II ions with temperature was confirmed by a combination of X-ray crystallography, variabletemperature Fourier transform infrared, variable-temperature magnetic susceptibility, and 57 Fe Mossbauer spectroscopy. Moreover, complexes 1• MeCN•Et 2 O and 1 exhibit a reversible single-crystal-to-single-crystal transformation, and complex 1 undergoes two-step SCO behavior with T 1/2 = 178 and 93 K accompanied by symmetry breaking in the structure.

We report a simple and highly sensitive solution concentration and refractive index (RI) sensor based on a microfiber knot resonator (MKR). The sensor was assembled using a flexible poly(trimethylene terephthalate) microfiber of 1.3 µm diameter. The resonance peak shifts due to the variation of the concentration of the ambient medium surrounding the MKR were detected. In the mass concentration range of 0.6–1.2%, the concentration sensitivity and resolution of the sensor are 1.7 nm/% and 1.2 × 10−3%, respectively. The highest measured sensitivity of the sensor is about 95.5 nm/RIU (RI unit) and the RI detection limit is about 2.1 × 10−5 in the RI range from 1.39 to 1.41.

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