The synthesis and structural characterization of water-soluble four-coordinate gold(I) complexes containing monodentate phosphine ligands are described. The ligands used are 1,3,5-triaza-7-phosphaadamantane (TPA) and its protonated and methylated derivatives, [HTPA]Cl and [MeTPA]I. Formation of the four-coordinate gold(I) species is favored by the small cone angle of the phosphine (102 degrees) and its ability to form a hydrogen-bonded network between the nitrogen atoms of the ligand and solvent water molecules. The gold center in all four complexes has a nearly regular tetrahedral geometry with an average P-Au-P angle of 109.5 degrees. [(HTPA)(3)(TPA)Au](PF6)(4) . 4H(2)O . CH3CN (1) crystallizes in the monoclinic space group P2(1)/c (No. 14) with cell constants a = 20.719(3) Angstrom, b = 15.606(2) Angstrom, c = 17.854(2) Angstrom, beta = 114.03(1)degrees, and Z = 4. Refinement of 4977 reflections and 650 parameters yields R = 0.0396 and R(w) = 0.0500. [(TPA)(4)Au]PF6 . 1.5HCl . H2O (2), crystallizes in the monoclinic space group C2/c (No. 15) with cell constants a = 33.036(7) Angstrom, b = 11.212(2) Angstrom, c = 31.503(5) Angstrom, b = 137.58(1)degrees and Z = 8. Refinement of 3835 reflections and 470 parameters yields R = 0.0351 and R(w) = 0.0403. [(TPA)(4)Au]Cl-4 . 6H(2)O (3) was characterized structurally in the cubic space group Fd (3) over bar m (No. 227) with cell constants a = b = c = 20.020(2) Angstrom and Z = 8. Refinement of 290 reflections and 28 parameters yields R = 0.0624 and R(w) = 0.1291. [(MeTPA)(4)Au](PF6)(5) . 2CH(3)CN (4) crystallizes in the monoclinic space group C2/c (No. 15) with cell, constants a = 23.337(3) Angstrom, b = 14.855(3) Angstrom, c = 35.317(5) Angstrom, b = 97.95(1)degrees, and Z = 8. Refinement of 7840 reflections and 621 parameters yields R = 0.0493 and R(w) = 0.0698.