The open cluster complex [Pt-6(mu-CO)(6)(mu-dppp)(2)(dppp)(2)], 1, dppp = Ph(2)P(CH2)(3)PPh(2), can encapsulate mercury(0) or thallium(I) with loss of dppp to give the cryptate cluster[Pt-6(mu(6)-M)(mu-CO)(6)(mu-dppp)(3)](n+), 2(M = Hg, n = 0) or 3(M = Tl, n = 1), respectively.