Gravar-mail: Bis[μ(2)-bis­(diphenyl­phosphan­yl)methane-κ(2) P:P′]bis­(μ(4)-diphenyl­phosphinato-κ(4) O:O:O′:O′)bis­(μ(2)-trifluoro­acetato-κ(2) O:O′)tetra­silver(I) acetonitrile disolvate