IntroductionWe are interested in the crystal packing of molecules that have a high proportion of phenyl groups over their surfaces, and therefore have the potential to engage in multiple phenyl embraces (MPE). This is part of an investigation of the variety and the strengths of multiple phenyl embraces as supramolecular motifs, and therefore of their value in crystal design and engineering. One variable for these molecules is the intramolecular conformational flexibility of the phenyl groups, and the extent to which they can flex to permit formation of MPE. In this context there are many molecules where the phenyl groups belong to PPh3ligands (or derivatives) and are partly constrained.1We have analysed the intramolecular and supramolecular stereochemistry of M–PPh3complexes,1,2and documented some high­order MPE and high symmetry lattices,3thenon­interference by substituents on the phenyl groups,4and the formation of a diamondoid lattice maintained only by MPE in [Cu{P(C6H4­4­OCH3)3}3]+ClO4−.5Here, we describe the crystallisation and crystal structure of (Ph3P)2Ag(O2C2O2)Ag(PPh3)2, analyse its crystal packing and its crystal supramolecularity in relation to that of similar molecules in which a tight, inflexible, oxalate­derived bridge,1, links two (Ph3P)2M moieties.The set of compounds considered involves five from the Cambridge structural database in addition to (Ph3P)2Ag(O2C2O2)Ag(PPh3)2(seeTable 1). There are three different crystal lattice (packing) types: one (A) inP1&cmb.macr; (including the new compound reported in this paper), and two different lattices (B and C) in space groupP21/c. It can be noted fromTable 1that there is no correlation of the molecular composition (M, X) with the lattice packing type, and accordingly this set of six compounds can be considered to demonstrate three substitutional polymorphs. In conventional definitions, polymorphs are crystal packing isomers of the one compound or molecule.6–11Substitutional polymorphism extends the definition to include molecules related by homologous atomic substitution, as is commonly pertinent in inorganic, coordination and organometallic contexts.12,13Known crystal structures of compounds in the set (Ph3P)2M(X1X3C2X2X4)M(PPh3)2CSD reference codeMX1X2X3X4Space groupApproximate cell dimensionsCrystal packing classa,b,c/Å(α),β, (γ)/°(Ph3P)2Cu(S2C2SO)Cu(PPh3)2has disordered S/O sites.This workAgOOOOP1&cmb.macr;9.9, 13.2, 13.464, 79, 88ADETZIL14CuSSSSP1&cmb.macr;10.2, 13.1, 13.563, 89, 78ATENFUN15CuSS/OS/OSP1&cmb.macr;10.2, 13.1, 13.5116, 90, 101ACEFMIJ16AgSOOSP21/c13.2, 11.9, 20.9101.4BYOFMUB17CuSSOOP21/c23.6, 13.7, 20.5104.1CYOFMUF17(no coordinates)AgSSOOP21/c23.6, 13.7, 20.5103.9C