Current Inorganic Chemistry (Discontinued) - Volume 7, Issue 2, 2017

Background: Porous coordination polymers (PCPs) are widely used as sorbents and catalysts for various processes. However, in the majority of cases the researchers can not predict the structure (and, as a consequence, the properties) of a new coordination polymer. The coordination polymer for special application is usually selected from the library of reported and characterized compounds, and then its properties are tested. This review deals with design of PCPs for the specific sorption, separation or catalytic applications. Objectives: The objective of the review was to analyze and summarize the cases when porous coordination polymers were specially designed for adsorption of certain substrates or catalysis of certain reaction. Methods: The review summarized the results, obtained by X-ray structure determination, measurements of different compounds adsorption from gaseous or liquid phase, and studies of catalytic and electrocatalytic properties. Catalysis of organic reaction in solutions at presence of solid PCPs is considered. Electrocatalytic activity was evaluated by cyclic voltammetry or by preparative electrolysis with solid electrodes, modified by film of PCP. Results: The approaches for creation of PCPs with desired sorption and catalytic properties were based on selection of the specific fragments, functional groups or units with desired properties before synthesis of the PCP, followed by creation of the PCP containing such specially designed units, or adjustment of the PCP's structure in order to satisfy certain requirement. Sorption selectivity could be adjusted by tuning of pore size in the PCP by variation of the ligand in isoreticular row of the compounds; introduction of the functional groups, which have different binding energy in respect to various substrates or tuning of the PCP's framework flexibility by appropriate choice of the ligands. Desired catalytic activity could be achieved by use of the fragments, groups or units, which showed desired properties in the separate experiments before their incorporation in the PCP. Conclusion: There are several methods for achievement of the target selectivity or catalytic activity, such as pre-synthetic choice or post-synthetic incorporation of functional groups, favorable for desired substrate binding, or active sites for desired catalytic or electrocatalytic reactions. Despite seeming difference of separation and catalytic applications, these methods are quite similar.

Background: Molecular molybdenum cluster sulphides are an unexpensive alternative to noble metal based homogenous catalysts. In this paper, we present the synthesis of the first PNP Mo3S4 derivative as well as the crystal structure of the isomer which contains the ligand bound in a bidentate fashion. The potential of this new complex as precursor for heterobimetallic systems is also analyzed. Objectives: The main objective of this study was to synthesize new cuboidal clusters containing the Mo3S4 unit and aminodiphosphanes. Methods: Standard Schlenk techniques were used for reactions carried out under nitrogen atmosphere. Electrospray ionization (ESI) mass spectra were recorded with a Quattro LC (quadrupole-hexapolequadrupole) mass spectrometer with an orthogonal Z-spray electrospray interface (Micromass, Manchester, UK). The cone voltage was set at 20 V using CH3CN as the mobile phase solvent. Nitrogen was employed as drying and nebulising gas. 31P NMR spectra were recorded on a Varian Innova 300 MHz using CD2Cl2 as solvent. Compounds (Bu4N)2[Mo3S7Cl6] and [Mo3S4Cl4(PPh3)3(H2O)2] were prepared by following literature procedures. The remaining reactants were obtained from commercial sources and used as received. Solvents were dried and degassed by standard methods before use. Results: The aminodiphosphane molybdenum (IV) cluster complex of formula [Mo3S4Cl3(Κ2(P,N)- PNP)3]Cl (PNP = bis[(2-di-i-propylphosphino)ethyl]amine) [Mo-1]Cl has been isolated in high yields by reacting [Mo3S4Cl4(PPh3)3(H2O)2] with stoichiometric amounts of the PNP ligand. Characterization of [Mo-1]+ by ESI-MS, 31P{1H} NMR and single-crystal X-ray diffraction confirms that aminodiphosphanes bind as bidentate ligands to the Mo3S4 unit leaving three uncoordinated phosphino groups. The dangling phosphino groups can substitute the chloride ligands and coordinate to the cluster core in the presence of AgBF4 to give the complex of formula [Mo3S4(Κ3-PNP)3](BF4)4 ([Mo-2](BF4)4). The tridentate coordination of the aminodiphosphane ligands to the Mo3S4 cluster unit in ([Mo-2]+ is confirmed by 31P{1H} NMR and elemental analysis. Conclusion: Our results indicated that Mo3S4 cluster cores can be functionalized with aminodiphosphine groups acting as bidentate or tridentate ligands.

Two new octahedral molybdenum cyanide cluster compounds, namely [{Zn(H2O)(en)2}{Zn(en)2}-Mo6Br6Se2(CN)6].2H2O (1) and [{Cu(H2O)(en)2}2Mo6Br6Se2(CN)6].2H2O (2) (en = ethylenediamine), have been synthetized as single crystals. 1 was obtained by slow diffusion of a solution containing [Mo6Br6Se2(CN)6]4- cluster units into a solution of zinc acetate and ethylenediamine. 2 was obtained by slow diffusion of an ammonia solution of [Mo6Br6Se2(CN)6]4- cluster units into a solution of cupper chloride and ethylenediamine. Both compounds were structurally characterized by single-crystal X-ray diffraction analysis. 1 is a bimetallic one dimensional coordination compound and it crystallizes in the orthorhombic system (P212121; Z = 4; a = 10.675(1) Ŭ b = 15.073(2) Ŭ c = 25.812(4) Ŭ V = 4153.3(1) ų at T = 150 K). 2 is a bimetallic H bonded three dimensional compound and it crystallizes in the monoclinic system (P21/c; Z = 2; a = 9.4281(4) Ŭ b = 11.0220(5) Å, c = 21.1494(9) Ŭ β = 100.053(2)°, V = 2164.03(16) ų at T = 296 K).

Background: Studies of transition metal complexes containing cubane core were inspired by the discovery of single-molecule magnetism in this family of compound. β-diketonates are quite often used for creation of cubane complexes. β-Ketosulfones, compounds containing S(O)2CH2C(O) fragment, to certain extent can be considered as analogues of β-diketones. It was intriguing to study the difference and similarities between the coordination behavior of β-diketones and β-ketosulfones, as well as the difference between the properties of 3d metal complexes with these ligands. Objectives: The aim of this work was to study the structure, magnetic and spectral properties of NiII and CoII complexes with a representative of β-ketosulfone family - analog of well-known β-diketonates. Methods: Crystallographic data were collected using Xcalibur Sapphire3 diffractometer with Mo-Kα radiation. UV/vis spectra were obtained using a Cary 300 machine in 350-800 nm range. TG experiments were carried our using Q1500 instrument in air. Reflectance spectra were measured on Beckman UV 5240 instrument. 1HNMR spectra were measured at 300 MHz on Bruker WP 100 SY instrument. Magnetic susceptibility measurements were carried out with Quantum Design PPMS-9 magnetometer operating in the range 300-2 K using field of 5000 Oe. Measurements were performed on polycrystalline samples sealed in a polyethylene bag and cover with mineral oil in order to prevent field-induced torquing of the crystals. The magnetic data were corrected for the sample holder, the mineral oil and the diamagnetic contribution. Results: The reaction of potassium salt of 2-(p-tolylsulfonyl)acetophenone (KL) with CoII and NiII nitrates resulted in the formation of tetranuclear complexes [Ni4(μ3-OCH3)4(H2O)3(CH3OH)(L)4]·H2O (1·H2O) and [Co4(μ3-OCH3)4(CH3OH)4(L)4]·4CH3OH·H2O (2·4CH3OH·H2O). Single crystal X-ray structure analysis showed that both 1·H2O and 2·4CH3OH·H2O possessed [M4(μ3-OCH3)4] tetranuclear cubane cores. Exchange coupling parameters were calculated for both NiII and CoII complexes by the analysis of temperature dependence of magnetic susceptibility by full-matrix diagonalization using a model, which included zero-field splitting (ZFS) of spin levels of metal ions and two (for 1) or one (for 2) different J parameters. All exchange interactions in 1 were found to be ferromagnetic, while for 2 it was concluded that the contributions of ZFS and exchange interactions were comparable. Conclusion: It was shown that β-sulfoketonate formed NiII and CoII cubanes, similarly to β-diketonates. Two new cubane-like polynuclear complexes were synthesized and characterized. For nickel complex all exchange interactions were ferromagnetic. The values of J for NiII complex were consistent with the ones, expected from the J vs. Ni-O-Ni angle correlation previously proposed for Ni4 β-diketonate cubanes. Magnetic properties of CoII analogue could be fitted using a model, which took into account ZFS of CoII and one J value. It was found that the contributions of ZFS and exchange interactions were comparable.

Background: Metal-organic frameworks (MOFs) have attracted much attention in recent research due to their potential applications in many areas, such as gas storage, carbon capture, catalysis, drug delivery, and so on. Despite their highly promising features, this class of materials suffers from poor chemical stability. Recently developed Zr-based MOFs have shown excellent stability and one of the challenges this field is facing now is the difficulty of integration of the MOFs in practical devices. Preparation of thin film is one of the approaches that can effectively immobilize the MOFs on surface for different applications. Objectives: The main objective of this study was to prepare thin films of recently developed Zr-based MOFs (UiO-66, UiO-66-NH2, UBMOF-8, and UBMOF-9 and their mixed-linker analogues) on conductive FTO substrate for potential future applications. Methods: Solvothermal approach was used to fabricate uniform crack-free microscopic thin films of Zrbased MOFs. Careful control of reaction conditions successfully led to the facile synthesis of Zr based metal-organic frameworks (Zr-MOFs) with substantial thermal stability. Taking advantage of mixedlinker approach, a series of Zr-based MIX-MOFs consisting of two isoreticular linkers, benzene-1,4-dicarboxylate (BDC) and 2-amibobenzene-1,4-dicarboxylate (ABDC), was successfully obtained. Further exploitation of mixed-linker approach onto other isoreticular system, 4,4′-stilbenedicarboxylate (SDC) and 2,2′-diamino-4,4158;‘-stilbenedicarboxylate (DASDC) effectively led to synthesis of MIX-MOFs with adjustable proportion of the two linkers. Results: A new facile solvothermal route for the synthesis of high-thermally stable Zr-based MOFs, namely UiO-66, UiO-66-NH2, UBMOF-9 and UBMOF-8 have been reported. Based on the nonfunctionalised/ functionalised mixed-linker systems of benzene-1,4-dicarboxylate/ 2-amibobenzene-1,4- dicarboxylate (BDC/ABDC) and 4,4′-stilbenedicarboxylate/ 2,2′-diamino-4,4′-stilbenedicarboxylate (SDC/DASDC), two series of mixed-linker Zr-based MOFs (MIX-MOFs), MIX-UiO-66 and MIXUBMOF have been synthesized with variable molar ratio of the two linkers, respectively. Tuning the thermal stability of MIX-UiO-66 and MIX-UBMOF series has been achieved by controlling the molar ratio of BDC/ABDC and SDC/DASDC, respectively. Thermal stability has been successfully enhanced by increasing the degree of substitution of functionalised (amino-) linker by the non-functionalised linker. Subsequently, reproducible and efficient solvothermal methods have been developed to construct uniform and fracture-free microscopic thin films of UiO-66, UiO-66-NH2, UBMOF-9, UBMOF-8, MIX-UiO-66-(3:1) and MIX-UBMOF (1:1) with exceptional crystallinity and adjustable thickness on electrically-conductive fluorine-doped tin oxide (FTO) substrates. All thin films exhibit high stability comparable to the bulk materials. Synergic utilisations of FT-IR and Raman spectroscopies have been used to get quantitative insight on both bulk material and thin films of the MIX-MOFs. Conclusion: This work reports the new approach of developing thin films of Zr-based MOFs on conductive FTO stubstrate and successful use of the mixed-linker approach to control the physical properties of the developed films.

Background: In the field of PCPs or MOF, besides strategies to design compounds with huge porosity, a great trend is the molecular engineering of the ligands. Their functionalization allows rendering walls of pores as an active surface able to specifically interact with guest molecules. Quite recently, bipyridinium (called also viologen) cores bearing carboxylate groups have been considered as ligands in the field of PCPs because of the electron acceptor character of bipyridinium units which are able to strongly interact with electron donor guest molecules. Objectives: The main objective of this study was to prepare new PCPs materials based on the viologencarboxylate ligand 1-(4-carboxyphenyl)-4,4'-bipyridinium. Methods: The compounds [Cd(hpc1)(BPDC)].2H2O (1) and [Cd2(hpc1)2(BPDC)(BPDC)].4H2O.DMF (2) have been synthesized from a mixture of Hhpc1Cl, Cd(NO3)2, H2BPDC -biphenyl-4,4′-dicarboxylic acid- (and H2BDC -terephtalic acid- for 2), DMF, EtOH and H2O heated at 100°C for 48h in a 25mL teflon-lined stainless steel autoclave, and slowly cooled to room temperature in 8 hours. Crystals were collected, washed with DMF and air-dried. X-ray diffraction data were collected on a Bruker-Nonius KAPPA-CDD with MoKα radiation (λ=0.71073 ũ for 1 (T= 293 K), and on an Agilent Supernova with CuKα radiation (λ=1.5418 ũ for 2 (T= 150 K). All experiments were carried out under a nitrogen atmosphere. The methanol adsorption isotherms of 1 and 2 at 298K were measured using a home-built McBain type balance. N2 adsorption isotherms at 77K were recorded on a Micromeritics ASAP 2020 instrument. In both cases before measurements the solids were degassed under vacuum (<10-5 hPa) at 150°C for 4h. Results: Two porous coordination polymers based on Cd2+ cations and the zwiterrionic viologencarboxylate ligand 4,4'-bipyridinium-1-(4-carboxyphenyl) (hpc1), [Cd(hpc1)BPDC].2H2O (1), and [Cd2(hpc1)2(BDC)(BPDC)] .4 H2O. DMF (2) have been discovered. The structures of these two compounds are isoreticular with half BPDC2- anions present in 1 being replaced by BDC2- anions in 2. The overall structures which result from the interpenetration of five 3D networks, exhibit channels containing guest molecules. Upon desorption, a breathing effect of the structure of 1 is observed as revealed by X-ray diffraction and methanol adsorption measurements. In fact, methanol adsorption on 1 occurs through a two-step isotherm characteristic of a gate opening in a flexible framework, while 2 exhibits a type I isotherm. Interestingly, the MeOH adsorption allows to suppose that the closed rhomboid channels which are present in the room temperature crystal structure of the as-synthesized compound become open to accommodate methanol molecules when the MeOH pressure is high (P/P°>0.5). Conclusion: Our results show that the association of Cd2+, the 4,4'-bipyridinium-1-(4-carboxyphenyl) viologen- carboxylate ligand and either the terephthalate anion BDC2- or the mixture of BDC2- and the biphenyl- 4,4′-dicarboxylate BPDC2- anion afford two isoreticular PCP compounds whose different structural characteristics, rigid vs flexible, have consequence on their adsorption properties.

Background: Incorporation of polyoxometalates (POMs) inside mesoporous materials such as Metal Organic Frameworks (MOFs) is a common strategy to prepare highly dispersed active species useful for catalytic applications. Nevertheless, a systematic study of the POMs insertion especially in MIL-101(Cr), one of the most used MOFs, appears necessary to clarify the nature of the species really incorporated. Objectives: Effects of the structure, charge and size of the POMs on the nature of inserted ionic species, their maximum loading, and their interaction with the MOF framework are investigated. Methods: POMs with the same Keggin structure (13 Å) but different charges were used, i.e., [PMo12O40]3-, [SiMo12O40]3-, [PMo11VVO40]4-, [PMo11VIVO40]5- with various counter-ions like H+, Na+, NH4 + or TBA+. Other compounds known for their stability and larger dimension were also used, namely the Dawson-type [PMo18O62]6-, the Preyssler-type [P5W30O110]15-, and the macro-ring [P8W48O184]40- with diameters of 15, 18 and 24 Å, respectively. MIL-101(Cr), chromium(III) terephthalate, synthesized in presence or absence of fluorhydric acid was used. Impregnation of POMs was performed in presence of a large excess of POMs to determine the maximum loading, or in proportion of the maximum loading. All compounds have been characterized by elemental analysis, infrared (IR), UV-Visible, and 31P NMR spectroscopies, X-Ray powder diffraction and thermo-diffractometry, and thermogravimetry. Textural properties of modified materials were also characterized using N2 adsorption isotherms. The POM interaction with the MOF was also investigated by in situ IR spectroscopy studies monitoring the adsorption of CO probe and the potential transformations of POM incorporated inside the cavities were studied. Results: All types of the counter ions of POMs are not incorporated inside the MOF, [Cr3Fx(H2O)3- xO(bdc)3](NO3)(1-x).nH2O ((bdc = benzene-1,4-dicarboxylate, x << 1), either in aqueous or organic solvent. Incorporation of POMs within the cavities of MIL-101(Cr) occurs by ionic exchange with nitrate ions. The maximum of POMs loading per large cavity depends on their negative charge, but also on the steric limitation of the structure type of POM: 8 for Keggin one and 4 for Dawson one. Thermodiffraction reveals an increase of the thermal stability of POM@MIL-101(Cr) until 280°C versus 220°C for the parent empty MOF. The study of CO adsorption by in situ IR spectroscopy indicates that the Lewis acid sites of MIL-101(Cr) are blocked by nitrate ions and incorporation of POM increases slightly their access. Furthermore, no significant Brønsted acid sites were detected. Subsequent ionic exchange of incorporated POMs with Cl-, ClO4 -, and other POMs were also studied. Finally, the pH stability of the MOF allows the partial hydrolysis of incorporated POM leading to unsaturated POM that can react with transition metal neutral complexes. Conclusion: No counter-ions of POMs are incorporated. Incorporation of POMs inside MIL-101(Cr) proceeds by ionic exchange. POMs thermally stabilize the MOF's framework and slightly increase the acess to Lewis acid sites. POMs can be removed by ionic exchange. We demonstrate that the host MIL- 101(Cr) behaves as a molecular reactor for the POMs chemistry.