Electronic and vibrational properties of a MOF-5 metal–organic framework: ZnO quantum dot behaviour

Semiconductor behavior of a metal-organic framework (MOF)

Upon light excitation MOF-5 behaves as a semiconductor and undergoes charge separation (electrons and holes) decaying in the microsecond time scale. The actual conduction band energy value was estimated to be 0.2 V versus NHE with a band gap of 3.4 eV. Photoinduced electron transfer processes to viologen generates the corresponding viologen radical cation, while holes of MOF-5 oxidizes N,N,N',N'-tetramethyl-p-phenylenediamine. One application investigated for MOF-5 as a semiconductor has been the shape-selective photocatalyzed degradation of phenol in aqueous solutions.

Hexanuclear iron(III) salicylaldoximato complexes presenting the [Fe6(mu3-O)2(mu2-OR)2]12+ core: syntheses, crystal structures, and spectroscopic and magnetic characterization

The use of salicylaldehyde oxime (H2salox) in iron(III) carboxylate chemistry has yielded two new hexanuclear compounds [Fe6(mu3-O)2(O2CPh)10(salox)2(L)2].xMeCN.yH2O [L = MeCONH2, x = 6, y = 0 (1); L = H2O, x = 2, y = 3 (2)]. Compound 1 crystallizes in the triclinic space group P with (at 25 degrees C) a = 13.210(8) A, b = 13.87(1) A, c = 17.04(1) A, alpha = 105.79(2) degrees , beta = 96.72(2) degrees , gamma = 116.69(2) degrees , V = 2578.17(2) A(3), and Z = 1. Compound 2 crystallizes in the monoclinic space group C2/c with (at 25 degrees C) a = 21.81(1) A, b = 17.93(1) A, c = 27.72(1) A, beta = 111.70(2) degrees , V = 10070(10) A(3), and Z = 4. Complexes 1 and 2 contain the [Fe6(mu3-O)2(mu2-OR)2]12+ core and can be considered as two [Fe3(mu3-O)] triangular subunits linked by two mu2-oximato O atoms of the salox2- ligands, which show the less common mu3:eta1:eta2:eta1 coordination mode. The benzoato ligands are coordinated through the usual syn,syn-mu2:eta1:eta1 mode. The terminal MeCONH2 ligand in 1 is the hydrolysis product of the acetonitrile solvent in the presence of the metal ions. Mössbauer spectra from powdered samples of 2 give rise to two well-resolved doublets with an average isomer shift consistent with that of high-spin Fe(III) ions. The two doublets, at an approximate 1:2 ratio, are characterized by different quadrupole splittings and are assigned to the nonequivalent Fe(III) ions of the cluster. Magnetic measurements of 2 in the 2-300 K temperature range reveal antiferromagnetic interactions between the Fe(III) ions, stabilizing an S = 0 ground state. NMR relaxation data have been used to investigate the energy separation between the low-lying states, and the results are in agreement with the susceptibility data.

Adsorption properties of HKUST-1 toward hydrogen and other small molecules monitored by IR

Among microporous systems metal organic frameworks are considered promising materials for molecular adsorption. In this contribution infrared spectroscopy is successfully applied to highlight the positive role played by coordinatively unsaturated Cu2+ ions in HKUST-1, acting as specific interaction sites. A properly activated material, obtained after solvent removal, is characterized by a high fraction of coordinatively unsaturated Cu2+ ions acting as preferential adsorption sites that show specific activities towards some of the most common gaseous species (NO, CO2, CO, N2 and H2). From a temperature dependent IR study, it has been estimated that the H2 adsorption energy is as high as 10 kJ mol(-1). A very complex spectral evolution has been observed upon lowering the temperature. A further peculiarity of this material is the fact that it promotes ortho-para conversion of the adsorbed H2 species.

Reactivity and Structural and Physical Studies of Tetranuclear Iron(III) Clusters Containing the [Fe4(μ3-O)2]8+ “Butterfly” Core: an FeIII4 Cluster with an S = 1 Ground State

The initial use of di-2-pyridyl ketone oxime [(py)2CNOH] in iron(III) carboxylate chemistry has yielded the tetranuclear complex [Fe4O2Cl2(O2CMe)2{(py)2CNO}4] (1). Compound 1 can be synthesized either by the 1:2:1 molar ratio reaction between Fe(III), MeCO2-, and (py)2CNOH (complex 1a) or by the 1:3 molar ratio reaction between [Fe3O(O2CMe)6(H2O)3]Cl and (py)2CNOH (complex 1b). The presence of N3- in both reaction mixtures has afforded the tetranuclear complex [Fe4O2(N3)2(O2CMe)2{(py)2CNO}4] (2), which can be alternatively synthesized by the reaction of 1 with N3-. Compound 1a crystallizes in the tetragonal space group /-4 with (at 25 degrees C) a = 35.06(2) A, b = 35.06(2) A, c = 13.255(6) A, V = 16293(2) A(3), and Z = 8. Compound 1b crystallizes in the monoclinic space group P2(1)/c with (at 25 degrees C) a = 22.577(7) A, b = 17.078(6) A, c = 17.394(6) A, beta = 93.50(1) degrees , V = 6694(4) A(3), and Z = 4. Compound 2 crystallizes in the triclinic space group P1 with (at 25 degrees C) a = 13.658(9) A, b = 15.815(9) A, c = 17.29(1) A, alpha = 97.08(3) degrees , beta = 98.55(3) degrees , gamma = 112.12(3) degrees , V = 3355(4) A(3), and Z = 2. The structures of 1 and 2 contain the [Fe4(mu3-O)2]8+ core comprising four Fe(III) ions in a "butterfly" disposition and two mu3-O2- ions, each bridging three Fe(III) ions forming the "wings" of the "butterfly". The Mössbauer spectra of 1b and 2 consist of composite quadrupole-split doublets, with parameters typical for high-spin Fe(III) in octahedral environments. Magnetic susceptibility measurements on 1a revealed antiferromagnetic interactions between the S = 5/2 ferric ions, with best-fit parameters being J(wb) = -40.2 cm(-1) and J(bb) = -59.4 cm(-1) (H = -2SigmaJiJj) for wingtip-body and body-body interactions, respectively, yielding an S = 1 ground state. Both wingtip-body and body-body interactions are well determined.