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杂化碳与氧配合四倍。我们也用同样的方法在中等高压（20 GPa）下获得了Ca2CO4的同质结构，然而，在4 GPa左右的压力释放时，Ca2CO4会发生非晶化。最近其他研究小组的研究表明，新型碳酸盐，即含有四面体配位sp3杂化碳的碳酸盐，也可以与铁，镁和锰阳离子形成（尽管在非常高的压力下，p bbb70gpa，并且是不可淬灭的化合物），现在似乎有可能这种新型碳酸盐在结构和化学上与传统碳酸盐一样多样化，特别是CO4 -基团可以通过角共享聚合，类似于SiO44 -基团。因此，我们提出了一个项目，其总体目标是建立对这种具有四面体配位sp3碳的新型碳酸盐新家族的晶体化学和晶体学理解。该方案包括通过传统碳酸盐的端元与氧化物或与Co2和选定的固溶体反应，合成含有Ni2+， Zn2+, Co2+, Cd2+, Eu2+， Ba2+和Pb2+的新型碳酸盐。该项目首先旨在澄清这些新型碳酸盐可以在激光加热的金刚石砧细胞中合成的p， t条件。目前，即使是少数已知的新型碳酸盐岩的稳定场也没有得到很好的约束，并且Sr2CO4的形成条件似乎跨越了一个非常大的范围，从至少20 - 90 GPa（这可能既不是下限也不是上限）。然后，我们的目标是通过结合原位拉曼光谱和同步加速器衍射，并辅以DFT计算，了解CO44−-基团的组成、合成条件和聚合之间的相互关系。那些可以在中等压力（< 20 GPa）下获得并可以淬火到环境条件下的新型碳酸盐，例如Sr2CO4，将使用大体积压力机通过NMR， EELS， IXS和弛豫量热法获得的毫克大小的样品进行进一步研究，以便为了解与传统碳酸盐的结合和性能差异提供基础。

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.