The structures of the series of two-coordinate gold(I) complexes {(Me(2)PhP)AuX}(n) where X is Cl, Br, or I have been examined by X-ray diffraction. The chloro complex crystallized in two separate polymorphic forms. Colorless hexagonal blocks of {(Me(2)PhP)AuCl}(3) crystallized in the monoclinic space group P2(1)/m with a = 12.141(4) Å, b = 8.433(2) Å, c = 14.834(3) Å, and beta = 94.15(2) degrees at 130 K with Z = 2. Refinement of 2837 reflections and 177 parameters yielded R = 0.066 and R(w) = 0.069. The complex consists of three nearly linear P-Au-Cl units that are connected by Au-Au contacts at 3.091(2) and 3.120(2) Å. Colorless prisms of {(Me(2)PhP)AuCl}(2) form in the orthorhombic space group P2(1)2(1)2(1) as described earlier (Cookson, P. D.; Tiekink, E. R. T. Acta Crystallogr. 1993, C49, 1602). The two nearly linear P-Au-Cl units are staggered and connected through a Au-Au bond (3.230(2) Å). Colorless rectangular prisms of {(Me(2)PhP)AuBr}(2) form in the monoclinic space group P2(1) with a = 9.572(5) Å, b = 8.757(3), and c = 12.915(7) at 130 K with Z = 2. Refinement of 2469 reflections with 118 parameters yielded R = 0.080 and R(w) = 0.084. {(Me(2)PhP)AuI}(2) is isomorphous with the bromo complex with a = 9.736(2) Å, b = 8.890(2) Å, and c = 13.160(5) Å at 130 K with Z = 2. Refinement of 2796 reflections with 119 parameters yielded R = 0.052 and R(w) = 0.058. These complexes are similar to the chloro dimer but with altered orientations of the phenyl substituent. The predicted order of ligand effects (Cl> Br > I) on Au-Au distances from quasi-relativistic calculations is borne out in the experimental values: 3.230 Å (Cl); 3.119 Å (Br); 3.104 Å (I). In dichloromethane, these complexes dissociate into monomeric units but there is some evidence for the presence of dimers in concentrated solutions of the iodide compound.

Crystals of {(Me(2)PhP)AuX}(n) (Me = methyl; Ph = phenyl; X = Cl, Br, I; n = 2, 3) show emission from two excited states. Both states are assigned a triplet multiplicity, on the basis of their lifetimes and zero-field splittings. The structured, higher energy emission originates at approximately 360 nm and has the greater relative intensity at low temperatures. It is assigned as intraligand phosphorescence from a phenyl-localized (3)pipi state. The unstructured, lower energy emission has a peak wavelength that varies in the range 630-730 nm. It is assigned as phosphorescence from the triplet state due to the gold-based sigma(p) <-- sigma(s,d) excitation. The corresponding singlet state is observed at 290-310 nm. The results of SCF-Xalpha-SW calculations on the model complexes H(3)PAuX and (H(3)PAuX)(2) are also presented.

High-spin and low-spin complexes of the iron(III) tetrakis(meso-cyclohexyl)porphyrin ((TCHP)FeIII) have been studied by means of 1-D and 2-D 1H NMR. The complete assignment of porphyrin and R-imidazole 1H resonances has been done on the basis of 2-D COSY and NOESY techniques as well as by selective deuteration of imidazole. The chemical shifts of pyrrole β-Hs have been used as the probe of the electronic state of an iron(III) metal ion. It has been found that cyanide coordinates to the high-spin (TCHP)FeIIICl complex, leading to the formation of the low-spin [(TCHP)FeIII(CN)2]-, with the rare (d xz d yz )4(d xy )1 ground electronic state (the pyrrole β-H resonance at 12.01 ppm at 293 K in CD3OD). A contribution of two electronic configurations, (d xy )2(d xz d yz )3 and (d xz d yz )4(d xy )1, to the ground state of the metal ion has been invoked for the low-spin [(TCHP)FeIII(R-Im)2]+ complexes. Characteristic 1H NMR shifts for these complexes include the pyrrole resonance at 2.81 ppm accompanied by the markedly upfield shifted imidazole resonances at −19.67 ppm (2-H), −10.58 ppm (4-H), −4.05 ppm (5-H), and 0.97 ppm (1-H). An admixture of a (d xz d yz )4(d xy )1 configuration into the ground electronic state increases in the order imidazole (ImH) < 1-methylimidazole (1-MeIm) < 1,2-dimethylimidazole (1,2-diMeIm), following an enlargement of the axial ligand steric hindrance. The rotation of the 1,2-diMeIm around Fe−N bond in the low-spin [(TCHP)FeIII(1,2-diMeIm)2]+ complex is slow on the 1H NMR time scale even at 293 K. Consequently four β-H resonances and the diastereotopy of the cyclohexyl meso-substituents have been observed. The meso-cyclohexyl groups rotate freely at temperature above 243 K, whereas the frozen rotation below 233 K leads to the formation of additional rotational isomers as demonstrated by multiplicity of β-H resonances for high-spin and low-spin complexes studied.