Syntheses And Properties Of Tetrazolate-Based Coordination Polymers

In this dissertion,14coordination polymers besed on the tetrazolate ligands（1,5-bis（5-tetrazolo）-3-oxapentane and tetrazole） have been synthesized andcharacterized mainly through in situ generated ligand and/or in situ metal redoxmethods. Pertinent properties such as fuel gas and CO₂storage, molecule magnets,and optics were thoroughly studied. Importantly, the cubic aromaticity of the M₈（M=Fe, Co, and Zn） cubic core in12-14was first discovered. Details are as following:1. Ten novel coordination polymers （1-10） based on1,5-bis（5-tetrazolo）-3-oxapentane ligand have been successfully synthesized under room temperatureand hydrothermal conditions and structurally characterized. For1-6,photoluminescence properties and influence of the inorganic anions on theirstructures were studied. The desolvated phase of7can adsorb I₂molecules, andthe locations of I₂molecules are unambiguously identified by single-crystal X-raydiffraction. The interactions between I₂molecules and framework wereinvestigated. It should be noted that the formations of chiral7and achiral8significantly depend on the reaction temperature.9with a sod topology wassynthesized and its CO₂adsorption capacity and CO₂/CH4selectivity are amongthe highest values known to date. The molecular simulation showed that thestrong binding of CO₂is attributed to multipoint interactions and possibly nomajor binding exists for CO₂adsorption. It is the first time to utilize multipointinteraction strategy to enhance the CO₂adsorption capacities of MOFs.2. Using organonitriles as precursors, four novel coordination polymers containingM₈cubic core （M=Zn （11and12）, Co （13）, Fe （14）） have been synthesized viain situ generated ligand and/or in situ metal redox under hydrothermal conditions.Both the experiments （single crystal X-ray diffraction, powder X-ray diffraction,thermal gravimetric, raman spectroscopy, X-ray photoelectron spectroscopy, andX-ray absorption spectroscopy） and systematical quantum chemical calculationsrevealed that the Zn8core of11and12contain direct Zn-Zn bonds and the zinc atoms exist in a+1valence state. The Zn-Zn bond length （2.278） in12is theshortest known to date. These reported [ZnI₂]2+compounds exist in lowtemperature and are very sensitive to the air and moisture. Comparably, these[Zn₈^I] bearing compounds are surprisingly stable in solutions and in air. Theinvestigations on Zn-Zn bond nature and electronic structures of the [Zn₈^I]systems showed that eight delocalized molecular orbitals （MOs） of the [Zn₈^I] cubeare formed through overlap of the4s orbitals. Among them, four bonding orbitalswith a1and t2symmetry are fully occupied, giving a ground-state electronicconfiguration of （a1）2（t2）6, whereas four antibonding orbitals with t1and a2symmetry are completely empty with an electronic configuration of （a₂）⁰（t₁）⁰. Thisbonding pattern represents an unprecedented type of aromaticity, which we referto as cubic aromaticity. Such systems follow a previously unknown6n+2electroncounting rule. This special cubic aromaticity can account for the high stability of11and12.13and14are isostrutural to11by the crystal structure analyses, whichalso contain M₈cubic core. The magnetic studies show that13is asingle-molecule magnet. Based on the preliminary analysis of crystallographicdata and comparison with11, the oxidation states of Co （13） and Fe （14） shouldalso be+1, the relevant theory calculations are underway. Through the structuraland theoretical analyses of11-14, we anticipate that cubic aromaticity via s-, p-,d-and f-type atomic orbital overlap might widely exist in cubic metal clustermaterials.