Temperature-dependent ^(57)Fe Mossbauer spectra were collected on Fe_(x)Zn_(4-x)(1,4-benzenedicarboxylate)_(3)(Fe-MOF-5).When measured under an Ar atmosphere,the data at higher temperatures reveal thermal population o...Temperature-dependent ^(57)Fe Mossbauer spectra were collected on Fe_(x)Zn_(4-x)(1,4-benzenedicarboxylate)_(3)(Fe-MOF-5).When measured under an Ar atmosphere,the data at higher temperatures reveal thermal population of the lowest-lying electronic excited state,as expected for low symmetry tetrahedral ferrous ions.In the presence of N_(2),however,the temperature dependence becomes exaggerated and the spectra cannot be fitted to a single species.A fluctuating electric field gradient at the Fe nuclei best explains these data and suggests dynamic structural distortions induced by weak interactions with N_(2).This direct evidence of dynamic behaviour at MOF open metal sites is relevant for the use of MOF SBUs in catalysis,gas separation,and other applications that invoke similar phenomena.展开更多
基金supported by a CAREER award to M.D.from the National Science Foundation(DMR-1452612)The Mossbauer spectra were recorded at the NHMFL,which is funded by the NSF through the Cooperative Agreement No.DMR-1157490,the State of Florida,and the DOE+2 种基金The Mossbauer spectrometer was purchased using the NHMFL User Collaboration Grant Program(UCGP-5064)awarded to A.Opartial support through the Jack E.Crow NHFML fellowshipsupported in part by the NSF through TeraGrid resources provided by TACC under grant number TG-CHE150036 to S.A.S.
文摘Temperature-dependent ^(57)Fe Mossbauer spectra were collected on Fe_(x)Zn_(4-x)(1,4-benzenedicarboxylate)_(3)(Fe-MOF-5).When measured under an Ar atmosphere,the data at higher temperatures reveal thermal population of the lowest-lying electronic excited state,as expected for low symmetry tetrahedral ferrous ions.In the presence of N_(2),however,the temperature dependence becomes exaggerated and the spectra cannot be fitted to a single species.A fluctuating electric field gradient at the Fe nuclei best explains these data and suggests dynamic structural distortions induced by weak interactions with N_(2).This direct evidence of dynamic behaviour at MOF open metal sites is relevant for the use of MOF SBUs in catalysis,gas separation,and other applications that invoke similar phenomena.
