Peroxide-Promoted Disassembly Reassembly of Zr-Polyoxocations

Zr/Hf aqueous-acid clusters are relevant to inorganic nanolithography, metal–organic frameworks (MOFs), catalysis, and nuclear fuel reprocessing, but only two topologies have been identified. The (Zr4) polyoxocation is the ubiquitous square aqueous Zr/Hf-oxysalt of all halides (except fluoride), and prior-debated for perchlorate. Simply adding peroxide to a Zr oxyperchlorate solution leads to a striking modification of Zr4, yielding two structures identified by single-crystal X-ray diffraction. Zr25, isolated from a reaction solution of 1:1 peroxide/Zr, is fully formulated [Zr25O10(OH)50­(O2)5(H2O)40]­(ClO4)10·xH2O. Zr25 is a pentagonal assembly of 25 Zr-oxy/peroxo/hydroxyl polyhedra and is the largest Zr/Hf cluster topology identified to date. Yet it is completely soluble in common organic solvents. ZrTd, an oxo-centered tetrahedron fully formulated [Zr4(OH)4(μ-O2)2­(μ4-O)­(H2O)12]­(ClO4)6·xH2O, is isolated from a 10:1 peroxide/Zr reaction solution. The formation pathways of ZrTd and Zr25 in water were described by small-angle X-ray scattering (SAXS), pair distribution function (PDF), and electrospray ionization mass spectrometry (ESI-MS). Zr4 undergoes disassembly by 1 equiv of peroxide (per Zr) to yield small oligomers of Zr25 that assemble predominantly in the solid state, an unusual crystal growth mechanism. The self-buffering acidity of the Zr-center prevents Zr25 from remaining intact in water. Identical species distribution and cluster fragments are observed in the assembly of Zr25 and upon redissolution of Zr25. On the other hand, the 10:1 peroxide/Zr ratio of the ZrTd reaction solution yields larger prenucleation clusters before undergoing peroxide-promote disassembly into smaller fragments. Neither these larger cluster intermediates of ZrTd nor the smaller intermediates of Zr25 have yet been isolated and structurally characterized, and they represent an opportunity to expand this new class of group IV polycations, obtained by peroxide reactivity and ligation.Zr/Hf水酸簇（Zr/Hf aqueous-acid clusters）与无机纳米光刻（inorganic nanolithography）、金属有机框架（metal–organic frameworks, MOFs）、催化以及核燃料后处理相关，但目前仅报道两种拓扑结构（topology）。 (Zr4)多氧阳离子（polyoxocation）是所有卤化物（halide，氟化物（fluoride）除外）中普遍存在的方形锆/铪氧基盐，其高氯酸盐（perchlorate）形式此前存在学术争议。仅向锆氧基高氯酸盐溶液中加入过氧化物（peroxide），即可对Zr4产生显著修饰，得到两种经单晶X射线衍射（single-crystal X-ray diffraction）表征确认的结构。 从过氧化物与锆投料比为1:1的反应溶液中分离得到的Zr25，其完整表征的化学式为[Zr25O10(OH)50(O2)5(H2O)40](ClO4)10·xH2O。Zr25由25个锆-氧基/过氧基/羟基多面体组装为五角结构，是目前已报道的最大锆/铪簇拓扑结构，且可完全溶解于常见有机溶剂。 从过氧化物与锆投料比为10:1的反应溶液中分离得到的ZrTd，为氧中心四面体结构，其完整表征的化学式为[Zr4(OH)4(μ-O2)2(μ4-O)(H2O)12](ClO4)6·xH2O。 借助小角X射线散射（small-angle X-ray scattering, SAXS）、对分布函数（pair distribution function, PDF）与电喷雾电离质谱（electrospray ionization mass spectrometry, ESI-MS）等手段，阐明了ZrTd与Zr25在水中的形成路径。每摩尔锆对应加入1当量过氧化物时，Zr4会发生分解，生成Zr25的小尺寸低聚中间体，这类中间体主要在固态下发生组装，这是一种罕见的晶体生长机制。锆中心的自缓冲酸性会导致Zr25在水溶液中无法保持完整结构。在Zr25的组装过程与重新溶解过程中，均能观测到一致的物种分布与簇碎片特征。 另一方面，在过氧化物与锆投料比为10:1的ZrTd反应体系中，溶液会先形成更大尺寸的预成核簇（prenucleation cluster），随后发生过氧化物促进的分解，生成更小的碎片。目前既未分离得到ZrTd的此类大尺寸簇中间体，也未获得Zr25的小尺寸中间体并完成结构表征，而这些中间体为拓展通过过氧化物反应与配位作用得到的新型IV族多阳离子（group IV polycations）家族提供了研究契机。