Four crystalline dimers of the type, Au-2(I)(mu-PnP)(2)I-2, where PnP is PPh2(CH2)(n)PPh2 with n = 3, 4, 5, and 6 have been prepared and characterized by single-crystal X-ray diffraction and by P-31 NMR and infrared spectroscopy. Au-2(I)(mu-P3P)(2)I-2 and Au-2(I)(mu-P6P)(2)I-2 are centrosymmetric dimers with the planar (AuP2I)-P-I units oriented in antiparallel fashion. Remarkably, noncentrosymmetric Au-2(I)(mu-P5P)(2)I-2 has its planar (AuP2I)-P-I units oriented in parallel manner. Au-2(I)(mu-P4P)(2)(mu-I)(2) is unique, since it contains four-coordinate gold centers that are bridged by both iodide and diphosphine ligands. All four compounds are luminescent as solids at room temperature. B3LYP, B2PLYP, and spectroscopically oriented configuration interaction (SORCI) calculations have been conducted to give insight into the electronic and geometric structures of the ground and first excited triplet states of the three trigonal-planar complexes. The emission energies for the trigonal planar complexes are more strongly correlated with changes in the Au-I bond length rather than changes in the P-Au-P angle.