Triphenylhalophosphonium halides, Ph3PX2, form crystals comprising bridged linear cations [Ph3P–X–X–X–PPh3]+ where the X3 bridge is shortened from 6.56 Å in Cl–Cl–Cl to 6.37 Å in the Br–Br–Br system. It is proposed that this structure is stabilised by five-centre/six-electron (5c–6e) hypervalent interactions.
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