The solid state aggregation of two gold(I) nitrate complexes

Abstract

(Trimethylphosphine)gold(I) nitrate was prepared from the reaction of (Me₃P)AuCl and AgNO₃ in MeOH–CH₂Cl₂. Single crystals from CH₂Cl₂–pentane contain trimers [(Me₃P)Au(ONO₂)]₃ as sub-units of polymeric chains. The organization is based on short aurophilic Au–Au contacts. A discussion considering all other known (Me₃P)AuX structures leads to the conclusion that small, electronegative anions X favour aurophilic multi-coordination with longer Au⋯Au contacts, while less electronegative, bulky groups X induce dimerization with short Au⋯Au contacts. In all cases neighbouring molecules are arranged with their principal axes roughly perpendicular (staggered). Crystals of (^tBuNC)Au(ONO₂) grown from CH₂Cl₂–pentane at −25 °C were shown to be a 2∶1 dichloromethane solvate with a new meander-type structure, which is stable only at low temperature and under the standard pressure of a dichloromethane atmosphere. The structure is based on aurophilic interactions of a similar nature as in the solvent-free phase (obtained at 5 °C) as judged from the bond distance parameters, but the solvent molecules are accommodated in cavities formed through a different puckering of the chains. A comparison with other structures of (RNC)AuX molecules suggests that the parallel (eclipsed) head-to-tail alignment of the molecules is the preferred organization in the absence of other structure-determining effects.