Understanding the stability and structural diversity of carbonates containing sp3-hybridised carbon in tetrahedral coordination

我们最近开发了一种方法，使我们能够在环境条件下回收Sr2CO4，其中SP3杂化碳与氧配位四倍。我们还用同样的方法在中等高压(20 Gpa)下得到了等结构的Ca2CO4，但在大约4 Gpa的压力释放时，Ca2CO4发生了非晶化。由于其他研究小组最近的研究表明，新型碳酸盐，即含有四面体配位的sp3杂化碳的碳酸盐，也可以与铁、镁和锰阳离子(尽管在非常高的压力下，p&gt；70 Gpa，作为非猝灭化合物)形成，现在看来，这种新型碳酸盐在结构和化学上可能与传统碳酸盐一样多样化，特别是因为CO4−-基团可以通过角落共享的方式聚合，类似于SiO44−基团。因此，我们提出一个项目，主要目标是建立对这一新型碳酸盐家族的晶体化学和结晶学的理解，这些碳酸盐具有四面体配位的SP3-碳。这一建议包括通过传统碳酸盐的端元与氧化物或二氧化碳以及选定的固溶体反应来合成含有Ni2+、Zn2+、Co2+、Cd2+、Eu2+、Ba2+和Pb2+的新型碳酸盐。该项目首先旨在阐明在激光加热的金刚石顶压室中合成这些新型碳酸盐的p、T条件。目前，即使是已知的为数不多的几种新型碳酸盐的稳定性区域也没有得到很好的限制，形成条件似乎跨越了一个很大的范围，从至少20-90 Gpa到Sr2CO4(可能既不是上下限，也不是下限)。然后，我们的目标是通过结合原位拉曼光谱和同步辐射衍射，并辅之以密度泛函理论计算，来了解−-基团的组成、合成条件和聚合之间的相互依赖关系。那些可以在中压(&lt；20 Gpa)下获得并可以在常温条件下淬火的新型碳酸盐，如Sr2CO4，将使用大体积压力下获得的毫克大小的样品通过核磁共振、电子能谱、IXS和弛豫量热法进行进一步研究，以便为了解结合和性能与传统碳酸盐的不同提供基础。

We have recently developed an approach that allowed us to recover Sr2CO4,in which sp3-hy-bridized carbon is four-fold coordinated by oxygen, at ambient conditions. We also obtained with the same approach isostructural Ca2CO4 at moderately high pressures (20 GPa), which, however, amorphises on pressure-release at about 4 GPa. As recent studies by other groups have shown that novel carbonates, i.e. carbonates containing tetrahedrally coordinated sp3-hybridized carbon, can also be formed with iron-, magnesium- and manganese-cations (albeit at very high pressures, p >70 GPa, and as non-quenchable compounds), it now seems plausible that such novel carbonates may be structurally and chemically as diverse as conventional carbonates, especially as CO4 4−-groups may polymerize by corner-sharing, similar to SiO44−groups. We therefore propose a project with the overarching goal to establish a crystal chemical and crystallographic understanding of this new family of novel carbonates with tetrahedrally coordinated sp3-carbon. This proposal encompasses the synthesis of novel carbonates containing Ni2+, Zn2+, Co2+, Cd2+, Eu2+, Ba2+, and Pb2+, by reactions of end-members of conventional carbonates with either an oxide or with CO2 and of selected solid solutions. The project firstly aims to clarify the p,T-conditions at which these novel carbonates can be synthesized in laser-heated diamond anvil cells. Currently, the stability fields even of the few already known novel carbonates are not well constrained and the formation conditions seem to span a really large range from at least 20 - 90 GPa in Sr2CO4 (which probably are neither the lower nor the upper bounds). We then aim to understand the interdependence between composition, synthesis conditions and polymerization of CO44−-groups by combining in situ Raman spectroscopy and synchrotron diffraction, complemented by DFT calculations. Those novel carbonates which can be obtained at moderate pressure (< 20 GPa) and which can be quenched to ambient conditions, e.g. Sr2CO4, will be further studied using milligram-sized samples obtained with large volume presses by NMR, EELS, IXS and relaxation calorimetry in order to provide a basis for an understanding how bonding and properties differ from conventional carbonates.