The identity of, with a maximum loading of the iron complex at ∼11 wt% (0.16 molecules per Al3O元 moiety), was confirmed by PXRD and spectroscopic measurements. is a spin-crossover (SCO) compound with a gradual spin transition at 290-440 K for the bulk material (repeated cycles), associated with a pronounced colour change from the red low spin (LS) state to the white high-spin (HS) state. The synthesis of the NH2-MIL-101(Al) Metal-Organic Framework (MOF) with bis(hydrotris(pyrazolyl)borato)iron(ii),, added to the reaction medium yielded encapsulation products, denoted as, in the course of a 'bottle-around-the-ship' assembly. Sacrificial thermal treatment of 1 and 2 afforded ZnO and CuO oxides, respectively. All the calculated parameters are in good agreement with the experimental values obtained from single crystal X-ray diffraction, even for the BF4⁻ coordination polymer. HOMO–LUMO energy gap and NBO analysis of the new complexes were also calculated. Optimized geometry and vibrational frequencies of the title coordination polymers in the ground state were computed using B3LYP/6-31G(d,p) theory levels for structure optimization and coupling constant calculations. In particular, 1 represents the first example of BF4⁻ coordination to a Zn coordination polymer. Interestingly, the counteranions are found to be coordinated to the metal centers.
According to single crystal X-ray diffraction analysis, both polymers are isostructural and crystallize in the monoclinic space group, C2/m, with unit cell dimensions for 1 as a = 14.0391(17) Å, b = 16.899(2) Å, c = 8.8800(14) Å, β = 109.629(5)°, V = 1984.3(5) ų and Z = 2.
Both coordination polymers were characterized by FT-IR, UV-vis, and thermal analysis and the crystal structures were confirmed by single crystal XRD analysis. Two new coordination polymers, namely, ZnL2(BF4)2 (1) and CuL2(NO3)2 (2) were constructed from a new flexible acyclic cryptate-bis(1H-1,2,4-triazole) ligand. However, an internal pressure effect stabilizing the low-spin state is evidenced. The removal of lattice water molecules from 1♰.5H(2)O is not accompanied by a change of the morphology and of the space group, and the chain character is preserved. The freshly prepared sample of 1♰.5H(2)O, dried in air, was subjected to annealing at 390 K, and the obtained white compound (CF(3)SO(3))(2) (1) was found to exhibit a similar spin transition curve however much temperature was increased by (T(c) (↑) = 252 K and T(c) (↓) = 248 K). The phase transition is of first order, as determined by differential scanning calorimetry, with transition temperatures matching the ones determined by SQUID and Mössbauer spectroscopy. The material presents striking reversible thermochromism from white, at room temperature, to pink on quench cooling to liquid nitrogen, and acts as an alert towards temperature variations. The temperature dependence of the high-spin molar fraction derived from (57)Fe Mossbauer spectroscopy recorded on cooling below room temperature reveals an exceptionally abrupt single step transition between high-spin and low-spin states with a hysteresis loop of width 4 K (T(c) (↑) = 232 K and T(c) (↓) = 228 K) in agreement with magnetic susceptibility measurements. A β-aminoacid ester was successfully derivatized to yield to 4H-1,2-4-triazol-4-yl-propionate (βAlatrz) which served as a neutral bidentate ligand in the 1D coordination polymer (CF(3)SO(3))(2)♰.5H(2)O (1♰.5H(2)O).
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