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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°:
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'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.
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 |
| $\ce{[Fe2OBr6]^2-}$ | (μ-Oxo)bis[tribromoferrate(III)] | $\angle\ce{Fe-O-Fe} = 180°$ | Staggered | AWIDEQ |
| $\ce{[Be2F7]^3-}$ | (μ-Fluoro)bis[trifluoroberyllate(II)] | $\angle\ce{Be-O-Be} = 180°$ | Staggered | SEYHOT |
| $\ce{[Hg2I7]^3-}$ | (μ-Iodo)bis[triiodomercurate(II)] | $\angle\ce{Hg-O-Hg} = 180°$ | Staggered | GODDUY |
| $\ce{Zn(CH3)2}$ | Dimethylzinc | $\angle\ce{C-Zn-C} = 180°$ | Staggered | SAJDEO |
| $\ce{Cd(CH3)2}$ | Dimethylcadmium | $\angle\ce{C-Cd-C} = 180°$ | Eclipsed | AROPAA |
| $\ce{[Tl(CH3)2]^+}$ | Dimethylthallium(III) | $\angle\ce{C-Tl-C} = 179°$ | Eclipsed | DOMHAO |
| $\ce{[Cu(CH3)2]^-}$ | Dimethylcuprate(I) | $\angle\ce{C-Cu-C} = 180°$ | Staggered | DAZWIK |
| $\ce{[Cu(CF3)2]^-}$ | Bis(trifluoromethyl)cuprate(I) | $\angle\ce{C-Cu-C} = 180°$ | Staggered | NONVIW |
| $\ce{Hg(CF3)2}$ | Bis(trifluoromethyl)mercury | $\angle\ce{C-Hg-C} = 180°$ | Staggered | DTFMHG |
| $\ce{Hg(CHCl)2}$ | Bis(dichloromethyl)mercury | $\angle\ce{C-Hg-C} = 180°$ | Staggered | PIPFEZ |
| $\ce{[Mg(NH3)2]^2+}$ | Diamminemagnesium(II) | $\angle\ce{N-Mg-N} = 180°$ | Eclipsed | QUQQEB |
| $\ce{[Ag(CF3)2]^-}$ | Bis(trifluoromethyl)argentate(III) | $\angle\ce{C-Ag-C} = 180°$ | Staggered | ATABAB |
| $\ce{[Ag(NH3)2]^+}$ | Diamminesilver(I) | $\angle\ce{N-Ag-N} = 178°$ | Staggered | AWEGOZ |
| $\ce{[Au(CF3)2]^-}$ | Bis(trifluoromethyl)aurate(I) | $\angle\ce{N-Au-N} = 178°$ | Staggered | QOCPAC |
| $\ce{[Au(CH3)2]^-}$ | Dimethylaurate(I) | $\angle\ce{C-Au-C} = 180°$ | Eclipsed | WEMGOK |
| $\ce{[Au(NH3)2]^+}$ | Diamminegold(I) | $\angle\ce{N-Au-N} = 180°$ | Staggered | DIWZOB |
| $\ce{[Au(GeCl3)2]^-}$ | Bis(trichlorogermyl)aurate(I) | $\angle\ce{N-Au-N} = 180°$ | Staggered | RAGGEL |
@pawel provided here with multiple instances of apparently does «the trick». Indeed a bit ugly, I didn't identify a way to state something in line of "do this x times" to keep the underlying code easier to read and maintain. Eh bien ... it is an attempt. The edit affected both the chemical, as well as the mathematical formulae (first and third column).
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Feb 26 at 16:15
LaTeX and markdown / JavaScript) because there is trailing space in columns 1, 2, 3 as if there were trailing(!) padding. Or, markdown simply assumes non-proportional characters all on the same base line (no horizontal shrinkage for the sub- and superscripts, either) and hence has a particular difficult task. Maybe something for the site's engineers?
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Feb 26 at 17:44
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]. This electronic property has led to potential thermoelectric applications.
Reference
