The reactions of mercury(II) halides with the tetraphosphinitoresorcinarene complexes [P4X5], where M = Cu or Ag, X = Cl, Br, or I, and P-4 = (PhCH2CH2CHC6H2)(4)(O2CR)(4)(OPPh2)(4) with R = C6H11, 4-C6H4Me, C4H3S, OCH2CCH, or OCH2Ph, have been studied. The reactions of the complexes with HgX2 when M = Ag and X = Cl or Br occur with elimination of silver(I) halide and formation Of [P4Ag2X(HgX3)], but when M = Ag and X = I, the complexes [P4Ag4I5(HgI)] are formed. When M = Cu and X = I, the products were the remarkable capsule complexes [(P4Cu2I)(2)(Hg2X6)]. When M = Ag and X = I, the reaction with both Cul and HgI2 gave the complexes [P4Cu2I-(Hg2I5)]. Many of these complexes are structurally characterized as containing mercurate anions weakly bonded to cationic tetraphosphinitoresorcinarene complexes of copper(l) or silver(l) in an unusual form of host-guest interaction. In contrast, the complex [P4Ag4I5(HgI)] is considered to be derived from an anionic silver cluster with an iodomercury-(II) cation. Fluxionality of the complexes in solution is interpreted in terms of easy, reversible making and breaking of secondary bonds between the copper(l) or silver(l) cations and the mercurate anions.