The deep-red, air-stable complexes [Pt2Hg2(P(2)phen)(3)](PF6)(2), 1, or [Pd2Hg2(P(2)phen)(3)](PF6)(2), 2, (P(2)phen is 2,9-bis(diphenylphosphino)-1,10-phenanthroline) are most conveniently prepared by the stoichiometric reaction of either Pt(dba)(2) or Pd-2(dba)(3).CHCl3 (dba is dibenzylideneacetone) with P(2)phen and a single drop of elemental mercury in refluxing dichloromethane under an atmosphere of nitrogen, The P-31{H-1} NMR spectrum (CD3CN) of 1 shows a single sharp resonance at 43.1 ppm for the phosphorus atoms of the P2phen ligand with both Pt-195 ((1)J(P-Pt) = 4350 Hz) and Hg-199 ((2)J(P-Hg) = 620 Hz) satellites indicating the Hg-2(2+) unit is dynamic. Compound 2 has a similar resonance at 44.9 ppm with Hg-199 satellites ((2)J(P-Hg) = 638 Hz). The Hg-199 NMR (CD2Cl2, vs Hg(OAc)(2)) spectrum of 2 shows a heptet pattern at 833 ppm while for I a heptet superimposed on a doublet of heptets is observed at 770.8 ppm. The Pt-195 NMR spectrum of 1 displays a quartet at -3071 ppm with Hg-199 satellites and a (1)J(Pt-Hg) value of 1602 Hz. Characterization of 1 and of 2(BF4)(2) by single-crystal X-ray diffraction studies confirms the metallocryptand structure consisting of three phosphine-imine ligands forming a D-3 symmetric cage with a Hg-2(2+) ion in its center coordinated to two phenanthroline rings with the Hg-Hg bond (1, 2.7362(6); 2(BF4)(2), 2.6881(4) Angstrom) oriented perpendicular to the vector between the trigonally coordinated Pt(0) or Pd(0) atoms on each end. The Pt-Hg separations in 1 average 2.8143(6) Angstrom while in 2(BF4)(2) the average Pd-Hg separation is 2.7698(5) Angstrom, Excitation into the low energy excitation bands of 1 (475 nm) and 2 (430 nm) produces weak emissions centered at 593 nm with shoulders at 530 and 654 nm in 1 and centered at 524 nm with a shoulder at 545 nm in 2.