This is particularly so with oxohalides of coordination number 3 or 4 which, in accepting one or more electron pairs from a Lewis base, become 5- or 6-coordinate. Oxohalide anions such as can be seen as acid-base complexes of the oxohalide with more halide ions acting as Lewis bases. Another example is which forms the trigonal bipyramidal complex with the base trimethylamine.

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