Crystal structures exhibiting dimeric arrangement of tetrahedrally coordinated cations

I am looking for inorganic crystal structures that exhibit tetrahedrally coordinated cations arranged in a vertex-sharing dimer arrangement, where the cation - shared vertex - cation angle is close to 180°:


[![Feature of ionic arrangement I am looking for. The cations form a vertex-sharing dimeric structure](https://i.stack.imgur.com/Wj14D.png)](https://i.stack.imgur.com/Wj14D.png)


Are there any known instances of such crystal structures? If there are, then any number of examples would be welcome. If there are examples of compounds with just similar features (dimers with different coordination, for instance), then this would also be appreciated.




Given the unit must be isolated and should not be the subunit of an ionic network, the following graph model for [CCDC ConQuest](https://www.ccdc.cam.ac.uk/solutions/software/conquest/)'s (ver. 2022.3.0) query with restraints based on connectivity $(\mathrm T\_n)$ and fixed the central bond angle within 170° to 180° range gave 119 hits.


[![CCDC 2022 ConQuest's query](https://i.stack.imgur.com/yuJFk.png)](https://i.stack.imgur.com/yuJFk.png)


The unique found moieties are as follows with exemplary references from CSD database:





| Formula          | Name | Bridging angle           | Conf. | CSD ID |
| --- | --- | --- | --- | --- |
| $\ce{[Fe2OCl6]^2-}$ | (μ-Oxo)bis[trichloroferrate(III)] | $\angle\ce{Fe-O-Fe} = 180°$ | Staggered | [ADETIM](https://www.ccdc.cam.ac.uk/structures/Search?Ccdcid=ADETIM&DatabaseToSearch=Published) |
| $\ce{[Fe2OBr6]^2-}$ | (μ-Oxo)bis[tribromoferrate(III)] | $\angle\ce{Fe-O-Fe} = 180°$ | Staggered | [AWIDEQ](https://www.ccdc.cam.ac.uk/structures/Search?Ccdcid=AWIDEQ&DatabaseToSearch=Published) |
| $\ce{[Be2F7]^3-}$ | (μ-Fluoro)bis[trifluoroberyllate(II)] | $\angle\ce{Be-O-Be} = 180°$ | Staggered | [SEYHOT](https://www.ccdc.cam.ac.uk/structures/Search?Ccdcid=SEYHOT&DatabaseToSearch=Published) |
| $\ce{[Hg2I7]^3-}$ | (μ-Iodo)bis[triiodomercurate(II)] | $\angle\ce{Hg-O-Hg} = 180°$ | Staggered | [GODDUY](https://www.ccdc.cam.ac.uk/structures/Search?Ccdcid=GODDUY&DatabaseToSearch=Published) |
| $\ce{Zn(CH3)2}$ | Dimethylzinc | $\angle\ce{C-Zn-C} = 180°$ | Staggered | [SAJDEO](https://www.ccdc.cam.ac.uk/structures/Search?Ccdcid=SAJDEO&DatabaseToSearch=Published) |
| $\ce{Cd(CH3)2}$ | Dimethylcadmium | $\angle\ce{C-Cd-C} = 180°$ | Eclipsed | [AROPAA](https://www.ccdc.cam.ac.uk/structures/Search?Ccdcid=AROPAA&DatabaseToSearch=Published) |
| $\ce{[Tl(CH3)2]^+}$ | Dimethylthallium(III) | $\angle\ce{C-Tl-C} = 179°$ | Eclipsed | [DOMHAO](https://www.ccdc.cam.ac.uk/structures/Search?Ccdcid=DOMHAO&DatabaseToSearch=Published) |
| $\ce{[Cu(CH3)2]^-}$ | Dimethylcuprate(I) | $\angle\ce{C-Cu-C} = 180°$ | Staggered | [DAZWIK](https://www.ccdc.cam.ac.uk/structures/Search?Ccdcid=DAZWIK&DatabaseToSearch=Published) |
| $\ce{[Cu(CF3)2]^-}$ | Bis(trifluoromethyl)cuprate(I) | $\angle\ce{C-Cu-C} = 180°$ | Staggered | [NONVIW](https://www.ccdc.cam.ac.uk/structures/Search?Ccdcid=NONVIW&DatabaseToSearch=Published) |
| $\ce{Hg(CF3)2}$ | Bis(trifluoromethyl)mercury | $\angle\ce{C-Hg-C} = 180°$ | Staggered | [DTFMHG](https://www.ccdc.cam.ac.uk/structures/Search?Ccdcid=DTFMHG&DatabaseToSearch=Published) |
| $\ce{Hg(CHCl)2}$ | Bis(dichloromethyl)mercury | $\angle\ce{C-Hg-C} = 180°$ | Staggered | [PIPFEZ](https://www.ccdc.cam.ac.uk/structures/Search?Ccdcid=PIPFEZ&DatabaseToSearch=Published) |
| $\ce{[Mg(NH3)2]^2+}$ | Diamminemagnesium(II) | $\angle\ce{N-Mg-N} = 180°$ | Eclipsed | [QUQQEB](https://www.ccdc.cam.ac.uk/structures/Search?Ccdcid=QUQQEB&DatabaseToSearch=Published) |
| $\ce{[Ag(CF3)2]^-}$ | Bis(trifluoromethyl)argentate(III) | $\angle\ce{C-Ag-C} = 180°$ | Staggered | [ATABAB](https://www.ccdc.cam.ac.uk/structures/Search?Ccdcid=ATABAB&DatabaseToSearch=Published) |
| $\ce{[Ag(NH3)2]^+}$ | Diamminesilver(I) | $\angle\ce{N-Ag-N} = 178°$ | Staggered | [AWEGOZ](https://www.ccdc.cam.ac.uk/structures/Search?Ccdcid=AWEGOZ&DatabaseToSearch=Published) |
| $\ce{[Au(CF3)2]^-}$ | Bis(trifluoromethyl)aurate(I) | $\angle\ce{N-Au-N} = 178°$ | Staggered | [QOCPAC](https://www.ccdc.cam.ac.uk/structures/Search?Ccdcid=QOCPAC&DatabaseToSearch=Published) |
| $\ce{[Au(CH3)2]^-}$ | Dimethylaurate(I) | $\angle\ce{C-Au-C} = 180°$ | Eclipsed | [WEMGOK](https://www.ccdc.cam.ac.uk/structures/Search?Ccdcid=WEMGOK&DatabaseToSearch=Published) |
| $\ce{[Au(NH3)2]^+}$ | Diamminegold(I) | $\angle\ce{N-Au-N} = 180°$ | Staggered | [DIWZOB](https://www.ccdc.cam.ac.uk/structures/Search?Ccdcid=DIWZOB&DatabaseToSearch=Published) |
| $\ce{[Au(GeCl3)2]^-}$ | Bis(trichlorogermyl)aurate(I) | $\angle\ce{N-Au-N} = 180°$ | Staggered | [RAGGEL](https://www.ccdc.cam.ac.uk/structures/Search?Ccdcid=RAGGEL&DatabaseToSearch=Published) |


### Notes


1. There are different conformations as well as several entries that do not follow your cation-anion assignment exactly.
2. There is a bias for protons placement for the structures refined with Shelx due to the limitations of the riding model, so the confirmations for H-containing (methyl, ammonia) ligands *might be* incorrect.
3. The database contains about four structures with *linear* diethyl ether moieties, which I omitted as outliers.


 6

[Sodium sulfide](https://en.wikipedia.org/wiki/Sodium_sulfide) has an anti-fluoritecstructure, in which the sodium ions are tetrahedrally coordinated and the sulfide ions are cubically coordinated. If you look along any body diagonal of the cube of sodium ions coordinating the sulfur, you see your dimeric structure. Each sulfide ion is shared by four such dimeric arrangements oriented in different directions.


Magnesium silicide has a similar structure, but with less ionic bonding and more electron delocalization leading to a narrow indirect gap for semiconduction [[2]](https://doi.org/10.1002/ange.201701681). This electronic property has led to potential thermoelectric applications.


**Reference**


1. Dr. Hiroshi Mizoguchi, Dr. Yoshinori Muraba, Prof. Daniel C. Fredrickson, Dr. Satoru Matsuishi, Prof. Toshio Kamiya, Prof. Hideo Hosono (2017). "The Unique Electronic Structure of Mg2Si: Shaping the Conduction Bands of Semiconductors with Multicenter Bonding". *Angewandte Chemie* **129**(34), 10269-10273.
<https://doi.org/10.1002/ange.201701681>


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