UiO-66,reported in 2008,inspired the ongoing chemistry of group 4 metal–organic frameworks and it is still one of the most studied MOFs due to its exceptional stability.The tightness of their building blocks and bond...UiO-66,reported in 2008,inspired the ongoing chemistry of group 4 metal–organic frameworks and it is still one of the most studied MOFs due to its exceptional stability.The tightness of their building blocks and bond strength make it tough to access new topologies,unless the building blocks are changed or defect engineering is employed,which in turn lead to different nominal stoichiometries.However,well selected structure directing agents and harsh synthesis conditions allowed the isolation of the first polymorph of UiO-66,named EHU-30.Herein,we provide evidence for the generalization of the synthetic approach with four new EHU-30 isoreticular compounds,based on amino-functionalized linkers and zirconium and hafnium as metal centres:EHU-30-NH_(2)(M)and EHU-30-NHR(M)(M:Zr,Hf;R:2-carboxypropyl).The crystal structure analysis reveals that their framework is more porous than that of their polymorphic counterpart.Furthermore,due to the current relevance of MOFs in greenhouse gas capture and in water harvesting methodologies,we have explored CO_(2)and water vapour adsorption on the new polymorphic phases,by means of experimental and computational resources,and compared to the parent EHU-30.The amino functionalization makes the EHU-30 series more prone to CO_(2)and water vapour adsorption.Besides,the water adsorption isotherms show an interesting crossing sensitive to temperature,sorption cycles and functionalization of the linker,which has been attributed to a localized structural transformation from EHU-30 to UiO-66.Finally,time-of-flight(TOF)powder neutron diffraction experiments were also conducted to locate the preferred adsorption sites for water in functionalized and parent EHU-30 structures.展开更多
This work presents the synthesis and characterization of a new neutral mononuclear Fe(II)spin transition(ST)complex,[Fe^(II)(L)_(2)]^(0)(4Cl),where L is an asymmetrically substituted tridentate ligand 2-(3-(4-chloroph...This work presents the synthesis and characterization of a new neutral mononuclear Fe(II)spin transition(ST)complex,[Fe^(II)(L)_(2)]^(0)(4Cl),where L is an asymmetrically substituted tridentate ligand 2-(3-(4-chlorophenyl)-1H-1,2,4-triazol-5-yl)-6-(1H-pyrazol-1-yl)pyridine.4Cl exhibits a remarkably wide stable ST hysteresis loop ca.60 K wide embracing room temperature(T_^(↑)(1/2)=308 K and T_^(↓)(1/2)=248 K).Detailed structural,calorimetric and spectroscopic investigations,including X-ray diffraction with Rietveld analysis,Raman spectroscopy,and photoluminescence,reveal the crucial role of subtle structural changes within the crystal lattice in driving the cooperative spin transition.The DFT energy framework analysis highlights the interplay of balanced stabilizing and destabilizing intermolecular interactions that contribute to the observed hysteresis.Furthermore,the fluorescent properties of 4Cl exhibit distinct changes in emission intensity and wavelength upon spin state switching with emission color change from sky blue in the high spin state to violet in the low spin state.The compound is the first example of the spin transition compound with bistable fluorescence response at room temperature.展开更多
In this work,we have studied the structure and physical properties of a series of intermetallic compounds with the general formula CePd_(x)Ge_(2−x)(where,x=0.21,0.32,0.69).It was found that the compound crystallizes i...In this work,we have studied the structure and physical properties of a series of intermetallic compounds with the general formula CePd_(x)Ge_(2−x)(where,x=0.21,0.32,0.69).It was found that the compound crystallizes in three different phases with stoichiometries:CePd_(0.32)Ge_(1.68),CePd_(0.21)Ge_(1.79) and CePd_(0.69)Ge_(1.31) by varying the Pd to Ge ratio.While CePd_(0.32)Ge_(1.68) and CePd_(0.69)Ge_(1.31) crystallize in the hexagonal AlB2 structure type with the space group P6/mmm,CePd_(0.21)Ge_(1.79) crystallizes in the tetragonalα-ThSi_(2) structure type with the space group I41/amd.CePd_(0.69)Ge_(1.31) is in fact an ordered superstructure of CePd_(0.32)Ge_(1.68) with tripling of the c-lattice.Relative changes in the Pd/Ge ratio also impart substantial variation in their magnetic properties,although Ce is in the trivalent state in both the phases.CePd_(0.21)Ge_(1.79) shows metamagnetic behavior below 10 K whereas CePd_(0.69)Ge_(1.31) showed ferromagnetic behavior in the same temperature range.In addition to the metamagnetic behavior,CePd_(0.21)Ge_(1.79) also shows spin glass behavior at low temperature.DFT calculations were used to obtain ulterior information on the CePd_(0.69)Ge_(1.31) phase.Self-consistent calculations revealed that the ferromagnetic ordering of the ground state arises from the spins at the Ce and Pd sites.The observed sharp rise in the low temperature resistivity of CePd_(0.69)Ge_(1.31) is an indication of a pseudo-gap formation or possible Kondo behavior in the electronic density of states,enhancing the scattering of the charge carriers.Heat capacity measurements on CePd_(0.69)Ge_(1.31) suggest that it falls in the category of medium heavy fermion compounds.展开更多
基金the financial support from the Basque Government(IT1291-19)from the Spanish Ministry of Science and Innovation(PID2019-108028GB-C21,CTQ2017-92173-EXP and IJC2018-038162-I)+2 种基金Technical and human support provided by SGIker(UPV/EHU,MICINN,GV/EJ,and ESF)HPC support from C3UPO are also acknowledgedthe ISIS Neutron and Muon Source for the award of beam time on GEM(experiment RB1920440).
文摘UiO-66,reported in 2008,inspired the ongoing chemistry of group 4 metal–organic frameworks and it is still one of the most studied MOFs due to its exceptional stability.The tightness of their building blocks and bond strength make it tough to access new topologies,unless the building blocks are changed or defect engineering is employed,which in turn lead to different nominal stoichiometries.However,well selected structure directing agents and harsh synthesis conditions allowed the isolation of the first polymorph of UiO-66,named EHU-30.Herein,we provide evidence for the generalization of the synthetic approach with four new EHU-30 isoreticular compounds,based on amino-functionalized linkers and zirconium and hafnium as metal centres:EHU-30-NH_(2)(M)and EHU-30-NHR(M)(M:Zr,Hf;R:2-carboxypropyl).The crystal structure analysis reveals that their framework is more porous than that of their polymorphic counterpart.Furthermore,due to the current relevance of MOFs in greenhouse gas capture and in water harvesting methodologies,we have explored CO_(2)and water vapour adsorption on the new polymorphic phases,by means of experimental and computational resources,and compared to the parent EHU-30.The amino functionalization makes the EHU-30 series more prone to CO_(2)and water vapour adsorption.Besides,the water adsorption isotherms show an interesting crossing sensitive to temperature,sorption cycles and functionalization of the linker,which has been attributed to a localized structural transformation from EHU-30 to UiO-66.Finally,time-of-flight(TOF)powder neutron diffraction experiments were also conducted to locate the preferred adsorption sites for water in functionalized and parent EHU-30 structures.
基金This work was supported by the Spanish Ministerio de Ciencia,Innovación y Universidades[(MICIU/AEI/10.13039/501100011033)and FEDER/UE,through grant PID2023-150732NB-I00 and María de Maeztu(CEX2024-001467-M),and Ministry of Education and Science of Ukraine(24BF037-03).This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No.899546.Dr I.Gural'sky is acknowledged for preliminary optical reflectance measurements.T.D.thanks the Swiss Naeonal Science Foundaeon for financial support through grant Postdoct.Mobility P400P2_191108/1.
文摘This work presents the synthesis and characterization of a new neutral mononuclear Fe(II)spin transition(ST)complex,[Fe^(II)(L)_(2)]^(0)(4Cl),where L is an asymmetrically substituted tridentate ligand 2-(3-(4-chlorophenyl)-1H-1,2,4-triazol-5-yl)-6-(1H-pyrazol-1-yl)pyridine.4Cl exhibits a remarkably wide stable ST hysteresis loop ca.60 K wide embracing room temperature(T_^(↑)(1/2)=308 K and T_^(↓)(1/2)=248 K).Detailed structural,calorimetric and spectroscopic investigations,including X-ray diffraction with Rietveld analysis,Raman spectroscopy,and photoluminescence,reveal the crucial role of subtle structural changes within the crystal lattice in driving the cooperative spin transition.The DFT energy framework analysis highlights the interplay of balanced stabilizing and destabilizing intermolecular interactions that contribute to the observed hysteresis.Furthermore,the fluorescent properties of 4Cl exhibit distinct changes in emission intensity and wavelength upon spin state switching with emission color change from sky blue in the high spin state to violet in the low spin state.The compound is the first example of the spin transition compound with bistable fluorescence response at room temperature.
基金We thank the Jawaharlal Nehru Centre for Advanced Scientific Research,Sheikh Saqr Laboratory and Department of Science and Technology,India(DST),and the Council of Scientific and Industrial Research(CSIR)(01(2787)/14/EMR-II)for financial supportS.S thanks the CSIR for research fellowship,D.K.and P.H.thank the UGC-DAE CSR,Mumbai center for project fellowship(Project No.CRS-M-166)S.C.P thanks the DST for the Ramanujan fellowship(Grant SR/S2/RJN-24/2010).
文摘In this work,we have studied the structure and physical properties of a series of intermetallic compounds with the general formula CePd_(x)Ge_(2−x)(where,x=0.21,0.32,0.69).It was found that the compound crystallizes in three different phases with stoichiometries:CePd_(0.32)Ge_(1.68),CePd_(0.21)Ge_(1.79) and CePd_(0.69)Ge_(1.31) by varying the Pd to Ge ratio.While CePd_(0.32)Ge_(1.68) and CePd_(0.69)Ge_(1.31) crystallize in the hexagonal AlB2 structure type with the space group P6/mmm,CePd_(0.21)Ge_(1.79) crystallizes in the tetragonalα-ThSi_(2) structure type with the space group I41/amd.CePd_(0.69)Ge_(1.31) is in fact an ordered superstructure of CePd_(0.32)Ge_(1.68) with tripling of the c-lattice.Relative changes in the Pd/Ge ratio also impart substantial variation in their magnetic properties,although Ce is in the trivalent state in both the phases.CePd_(0.21)Ge_(1.79) shows metamagnetic behavior below 10 K whereas CePd_(0.69)Ge_(1.31) showed ferromagnetic behavior in the same temperature range.In addition to the metamagnetic behavior,CePd_(0.21)Ge_(1.79) also shows spin glass behavior at low temperature.DFT calculations were used to obtain ulterior information on the CePd_(0.69)Ge_(1.31) phase.Self-consistent calculations revealed that the ferromagnetic ordering of the ground state arises from the spins at the Ce and Pd sites.The observed sharp rise in the low temperature resistivity of CePd_(0.69)Ge_(1.31) is an indication of a pseudo-gap formation or possible Kondo behavior in the electronic density of states,enhancing the scattering of the charge carriers.Heat capacity measurements on CePd_(0.69)Ge_(1.31) suggest that it falls in the category of medium heavy fermion compounds.
