Covalent radii of four-co-ordinate copper(I), silver(I) and gold(I): crystal structures of [Ag(AsPh3)4]BF4 and [Au(AsPh3)4]BF4

Abstract
The complexes [Ag(AsPh 3 ) 4 ]BF 4 and [Au(AsPh 3 ) 4 ]BF 4 were prepared from AgBF 4 and 4 equivalents of AsPh 3 , and from equimolar quantities of [Au(AsPh 3 )Cl] and AgBF 4 and 3 equivalents of AsPh 3 , respectively, in dichloromethane solution. Single crystals of the two compounds are isomorphous (trigonal, space group R, Z = 6) and contain cations with a tetrahedral Ag/Au–As 4 core. From the Ag/Au–As distances measured at 199 K the covalent radii of four-co-ordinate silver(I) and gold(I) have been calculated using an accepted standard covalent radius for four-co-ordinate arsenic(III), r(As III ) = 1.20 Å; r(Au I ) = 1.37 Å is found to be 6% smaller than r(Ag I ) = 1.46 Å. This contraction reflects the strong influence of relativistic effects on atomic radii. From other data, r(Cu I ) for four-co-ordinate copper is estimated to be 1.29 Å.

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