Synthesis of Au(II) Fluoro Complexes and Their Structural and Magnetic Properties

Unlocking the catalytic potential of gold(II) complexes: a comprehensive reassessment

Gold(II) complexes, unlike their gold(I) and gold(III) counterparts, have been sparsely employed in the field of catalysis. This is primarily due to the challenges associated with isolating and characterising these open-shell species. However, these complexes offer a wide range of possibilities. On one hand, this intermediate oxidation state has proven to be more easily accessible through reduction and oxidation processes compared to the gold(I)/gold(III) redox couple, thereby facilitating potential homo-coupling and cross-coupling reactions. On the other hand, gold(II) exhibits Lewis acid behaviour, bridging the characteristics of the soft acid gold(I) and the hard acid gold(III). In this review, we focus on mono- and dinuclear gold(II) complexes, whether they are isolated and well-studied or proposed as intermediates in cross-coupling reactions induced by the action of oxidants or light. We delve into the unique reactivity and potential applications of these gold(II) species, shedding light on their role in this field. This comprehensive exploration aims to underscore the latent promise of gold(II) complexes in catalysis, offering insights into their structural and mechanistic aspects while highlighting their relevance in contemporary chemical transformations.

Stabilizing Au2+ in a mixed-valence 3D halide perovskite

Although Cu2+ is ubiquitous, the relativistic destabilization of the 5d orbitals makes the isoelectronic Au2+ exceedingly rare, typically stabilized only through Au-Au bonding or by using redox non-innocent ligands. Here we report the perovskite Cs4AuIIAuIII2Cl12, an extended solid with mononuclear Au2+ sites, which is stable to ambient conditions and characterized by single-crystal X-ray diffraction. The 2+ oxidation state of Au was assigned using 197Au Mössbauer spectroscopy, electron paramagnetic resonance, and magnetic susceptibility measurements, with comparison to paramagnetic and diamagnetic analogues with Cu2+ and Pd2+, respectively, as well as to density functional theory calculations. This gold perovskite offers an opportunity to study the optical and electronic transport of the uncommon Au2+/3+ mixed-valence state and the characteristics of the elusive Au2+ ion coordinated to simple ligands. Compared with the perovskite Cs2AuIAuIIICl6, which has been studied since the 1920s, Cs4AuIIAuIII2Cl12 exhibits a 0.7 eV reduction in optical absorption onset and a 103-fold increase in electronic conductivity.

Crystal Growth from Anhydrous HF Solutions of M2+ (M = Ca, Sr, Ba) and [AuF6]-, Not Only Simple M(AuF6)2 Salts

Crystal growth from anhydrous HF solutions of M²⁺ (M = Ca, Sr, Ba) and [AuF₆]⁻ (molar ratio 1:2) gave [Ca(HF)₂](AuF₆)₂, [Sr(HF)](AuF₆)₂, and Ba[Ba(HF)]₆(AuF₆)₁₄. [Ca(HF)₂](AuF₆)₂ exhibits a layered structure in which [Ca(HF)₂]²⁺ cations are connected by AuF₆ units, while the crystal structure of Ba[Ba(HF)]₆(AuF₆)₁₄ exhibits a complex three-dimensional (3-D) network consisting of Ba²⁺ and [Ba(HF)₂]²⁺ cations bridged by AuF₆ groups. These results indicate that the previously reported M(AuF₆)₂ (M = Ca, Sr, Ba) compounds, prepared in the anhydrous HF, do not in fact correspond to this chemical formula. When the initial M²⁺/[AuF₆]⁻ ratio was 1:1, single crystals of [M(HF)](H₃F₄)(AuF₆) were grown for M = Sr. The crystal structure consists of a 3-D framework formed by [Sr(HF)]²⁺ cations associated with [AuF₆]⁻ and [H₃F₄]⁻ anions. The latter exhibits a Z-shaped conformation, which has not been observed before. Single crystals of M(BF₄)(AuF₆) (M = Sr, Ba) were grown when a small amount of BF₃ was present during crystallization. Sr(BF₄)(AuF₆) crystallizes in two modifications. A high-temperature α-phase (293 K) crystallized in an orthorhombic unit cell, and a low-temperature β-phase (150 K) crystallized in a monoclinic unit cell. For Ba(BF₄)(AuF₆), only an orthorhombic modification was observed in the range 80–230 K. An attempt to grow crystals of Ca(BF₄)(AuF₆) failed. Instead, crystals of [Ca(HF)](BF₄)₂ were grown and the crystal structure was determined. During prolonged crystallization of [AuF]₆^– salts, moisture can penetrate through the walls of the crystallization vessel. This can lead to partial reduction of Au(V) to A(III) and the formation of [AuF₄]⁻ byproducts, as shown by the single-crystal growth of [Ba(HF)]₄(AuF₄)(AuF₆)₇. Its crystal structure consists of [Ba(HF)]²⁺ cations connected by AuF₆ octahedra and square-planar AuF₄ units. The crystal structure of the minor product [O₂]₂[Sr(HF)]₅[AuF₆]₁₂·HF was also determined.

Crystal growth from anhydrous HF solutions of M²⁺ (M = Ca, Sr, Ba) and [AuF₆]⁻ (molar ratio 1:2) gave [Ca(HF)₂](AuF₆)₂ and Ba[Ba(HF)]₆(AuF₆)₁₄. These results indicate that the previously reported M(AuF₆)₂ (M = Ca, Sr, Ba) compounds do not correspond to this chemical formula. When the initial Sr²⁺/[AuF₆]⁻ ratio was 1:1, crystals of [Sr(HF)](H₃F₄)(AuF₆) were grown. Single crystals of M(BF₄)(AuF₆) (M = Sr, Ba) were obtained when a small amount of BF₃ was present during crystallization. The crystal structures of [Ba(HF)]₄(AuF₄)(AuF₆)₇, [O₂]₂[Sr(HF)]₅[AuF₆]₁₂·HF, and Ca(BF₄)(AuF₆) byproducts were also determined.

Unexpected persistence of cis-bridged chains in compressed AuF3

Raman scattering measurements indicate that cis-bridged chains are retained in AuF3 even at a compression of 45 GPa - in contrast to meta-GGA calculations suggesting that structures with such motifs are thermodynamically unstable above 4 GPa. This metastability implies that novel gold fluorides (e.g. AuF2) might be attainable at lower pressures than previously proposed.

Evolutionary Algorithm-based Crystal Structure Prediction for Gold(I) Fluoride

Solid gold(I) fluoride remains as an unsynthesized and uncharacterized compound. We have performed a search for potential gold(I) fluoride crystal structures using USPEX evolutionary algorithm and dispersion-corrected hybrid density functional methods. Over 4000 AuF crystal structures have been investigated. Behavior of the AuF crystal structures under pressure was studied up to 25 GPa, and we also evaluated the thermodynamic stability of the hypothetical AuF crystal structures with respect to AuF₃ , AuF₅ , and Au₃ F₈ . Mixed-valence compound Au₃ [AuF₄ ] with Au atoms in various formal oxidation states emerged as the thermodynamically most stable AuF species.

Quest for Compounds at the Verge of Charge Transfer Instabilities: The Case of Silver(II) Chloride †

Electron-transfer processes constitute one important limiting factor governing stability of solids. One classical case is that of CuI2, which has never been prepared at ambient pressure conditions due to feasibility of charge transfer between metal and nonmetal (CuI2 → CuI + ½ I2). Sometimes, redox instabilities involve two metal centers, e.g., AgO is not an oxide of divalent silver but rather silver(I) dioxoargentate(III), Ag(I)[Ag(III)O2]. Here, we look at the particularly interesting case of a hypothetical AgCl2 where both types of redox instabilities operate simultaneously. Since standard redox potential of the Ag(II)/Ag(I) redox pair reaches some 2 V versus Normal Hydrogen Electrode (NHE), it might be expected that Ag(II) would oxidize Cl− anion with great ease (standard redox potential of the ½ Cl2/Cl− pair is + 1.36 V versus Normal Hydrogen Electrode). However, ionic Ag(II)Cl2 benefits from long-distance electrostatic stabilization to a much larger degree than Ag(I)Cl + ½ Cl2, which affects relative stability. Moreover, Ag(II) may disproportionate in its chloride, just like it does in an oxide; this is what AuCl2 does, its formula corresponding in fact to Au(I)[Au(III)Cl4]. Formation of polychloride substructure, as for organic derivatives of Cl3− anion, is yet another possibility. All that creates a very complicated potential energy surface with a few chemically distinct minima i.e., diverse polymorphic forms present. Here, results of our theoretical study for AgCl2 will be presented including outcome of evolutionary algorithm structure prediction method, and the chemical identity of the most stable form will be uncovered together with its presumed magnetic properties. Contrary to previous rough estimates suggesting substantial instability of AgCl2, we find that AgCl2 is only slightly metastable (by 52 meV per formula unit) with respect to the known AgCl and ½ Cl2, stable with respect to elements, and simultaneously dynamically (i.e., phonon) stable. Thus, our results point out to conceivable existence of AgCl2 which should be targeted via non-equilibrium approaches.

Theoretical investigation of the valence states in Au via the Au-F compounds under high pressure

In addition to the known Au3+ and Au5+, it has recently been shown that Au is likely to possess unusual valence states in compressed Au-F compounds. However, our simulations reveal that polymeric ground-state AuF4 shows an unexpected 6-fold coordination rather than a 4-fold one, indicating that more complete comprehending on the anomalous Au4+ is highly required. To fully understand the nature and origin of anomalous valence states in Au, we have extensively investigated the ground-state structures of Au-F compounds at high pressures using quantum mechanical computational methods. As a consequence, we identify several previously unreported (stable) AuF2, AuF3 and AuF4 structures. Our results extend the known polymorphism of AuFn compounds and offer a fundamental understanding of the origin of unusual valence states in Au that prevail at high pressure.

Old puzzle of incommensurate crystal structure of calaverite AuTe2 and predicted stability of novel AuTe compound

Gold is a very inert element, which forms relatively few compounds. Among them is a unique material-mineral calaverite, [Formula: see text] Besides being the only compound in nature from which one can extract gold on an industrial scale, it is a rare example of a natural mineral with incommensurate crystal structure. Moreover, it is one of few systems based on Au, which become superconducting (at elevated pressure or doped by Pd and Pt). Using ab initio calculations we theoretically explain these unusual phenomena in the picture of negative charge-transfer energy and self-doping, with holes being largely in the Te [Formula: see text] bands. This scenario naturally explains incommensurate crystal structure of [Formula: see text], and it also suggests a possible mechanism of superconductivity. An ab initio evolutionary search for stable compounds in the Au-Te system confirms stability of [Formula: see text] and [Formula: see text] and leads to a prediction of an as yet unknown stable compound AuTe, which until now has not been synthesized.

Structure and reactivity of a mononuclear gold(II) complex

Mononuclear gold(II) complexes are very rare labile species. Transient gold(II) species have been suggested in homogeneous catalysis and in medical applications, but their geometric and electronic structures have remained essentially unexplored: even fundamental data, such as the ionic radius of gold(II), are unknown. Now, an unprecedentedly stable neutral gold(II) complex of a porphyrin derivative has been isolated, and its structural and spectroscopic features determined. The gold atom adopts a 2+2 coordination mode in between those of gold(III) (four-coordinate square planar) and gold(I) (two-coordinate linear), owing to a second-order Jahn-Teller distortion enabled by the relativistically lowered 6s orbital of gold. The reactivity of this gold(II) complex towards dioxygen, nitrosobenzene and acids is discussed. This study provides insight on the ionic radius of gold(II), and allows it to be placed within the homologous series of nd⁹ Cu/Ag/Au divalent ions and the 5d^8/9/10 Pt/Au/Hg 'relativistic' triad in the periodic table.

Investigation of gold fluorides and noble gas complexes by matrix-isolation spectroscopy and quantum-chemical calculations

Noble with a difference: Matrix-isolation experiments and quantum-chemical calculations have led to the characterization of two new compounds, namely first open-shell binary gold fluoride, AuF(2), and a NeAuF complex. Moreover, ArAuF, AuF(3), Au(2)F(6), and monomeric AuF(5) have been produced and identified under cryogenic conditions in neon and argon matrices.

Synthesis and structure of a dinuclear gold(II) complex with terminal fluoride ligands

The potential for reductive elimination of fluorine from dinuclear gold(II) for catalysis has prompted our efforts to synthesize a dinuclear gold(II) fluoride complex. This has been achieved with bis(2,6-dimethylphenyl)formamidinate bridging ligands. In order to obtain this product, it was necessary first to synthesize the corresponding dinuclear gold(II) nitrate, which reacts readily with KF in a metathesis reaction. The nitrate complex and fluoride complexes have been structurally characterized. The Au-Au distance in the dinuclear fluoride, 2.595 Å, is longer than the distance found in the analogous chloride complex, 2.567 Å. This result is consistent with the presence of a fluoride "π electron effect" on the filled Au 5d orbitals. The Raman spectrum shows an Au-Au stretch at 206 cm(-1), which agrees with Woodruff's rules and the density functional theory computational model used for modeling the complex.

How PEO-PPO-PEO triblock polymer micelles control the synthesis of gold nanoparticles: temperature and hydrophobic effects

Aqueous micellar solutions of F68 (PEO(78)-PPO(30)-PEO(78)) and P103 (PEO(17)-PPO(60)-PEO(17)) triblock polymers were used to synthesize gold (Au) nanoparticles (NPs) at different temperatures. All reactions were monitored with respect to reaction time and temperature by using UV-visible studies to understand the growth kinetics of NPs and the influence of different micellar states on the synthesis of NPs. The shape, size, and locations of NPs in the micellar assemblies were determined with the help of TEM, SEM, and EDS analyses. The results explained that all reactions were carried out with the PEO-PPO-PEO micellar surface cavities present at the micelle-solution interface and were precisely controlled by the micellar assemblies. Marked differences were detected when predominantly hydrophilic F68 and hydrophobic P103 micelles were employed to conduct the reactions. The UV-visible results demonstrated that the reduction of gold ions into nucleating centers was channeled through the ligand-metal charge-transfer complex (LMCT) and carried out by the surface cavities. Excessive hydration of the surface cavities in the case of F68 micelles produced a few small NPs, but their yield and size increased as the micelles were dehydrated under the effect of increasing temperature. The results concluded that the presence of well-defined predominantly hydrophobic micelles with a compact micelle-solution interfacial arrangement of surface cavities ultimately controlled the reaction.

Redox Non-innocence of Thioether Macrocycles: Elucidation of the Electronic Structures of Mononuclear Complexes of Gold(II) and Silver(II)

The mononuclear +2 oxidation state metal complexes [Au([9]aneS(3))(2)](2+) and [Ag([18]aneS(6))](2+) have been synthesized and characterized crystallographically. The crystal structure of the Au(II) species [Au([9]aneS(3))(2)](BF(4))(2) shows a Jahn-Teller tetragonally distorted geometry with Au-S(1) = 2.839(5), Au-S(2) = 2.462(5), and Au-S(3) = 2.452(5) A. The related Ag(II) complex [Ag([18]aneS(6))](ClO(4))(2) has been structurally characterized at both 150 and 30 K and is the first structurally characterized complex of Ag(II) with homoleptic thioether S-coordination. The single-crystal X-ray structure of [Ag([18]aneS(6))](ClO(4))(2) confirms octahedral homoleptic S(6)-thioether coordination. At 150 K, the structure contains two independent Ag(II)-S distances of 2.569(7) and 2.720(6) A. At 30 K, the structure retains two independent Ag(II)-S distances of 2.615(6) and 2.620(6) A, with the complex cation retaining 3-fold symmetry. The electronic structures of [Au([9]aneS(3))(2)](2+) and [Ag([18]aneS(6))](2+) have been probed in depth using multifrequency EPR spectroscopy coupled with DFT calculations. For [Au([9]aneS(3))(2)](2+), the spectra are complex due to large quadrupole coupling to (197)Au. Simulation of the multifrequency spectra gives the principal g values, hyperfine (A) and quadrupole (P) couplings, and furthermore reveals non-co-incidence of the principal axes of the P tensor with respect to the A and g matrices. These results are rationalized in terms of the electronic and geometric structure and reveal that the SOMO has ca. 30% Au 5d(xy)() character, consistent with DFT calculations (27% Au character). For [Ag([18]aneS(6))](2+), detailed EPR spectroscopic analysis confirms that the SOMO has ca. 26% Ag 4d(xy)() character and DFT calculations are consistent with this result (22% Ag character).

Structure and Bonding in Silver Halides. A Quantum Chemical Study of the Monomers: Ag2X, AgX, AgX2, and AgX3 (X = F, Cl, Br, I)

The molecular structure of all silver halide monomers, Ag(2)X, AgX, AgX(2), and AgX(3), (X = F, Cl, Br, I), have been calculated at the B3LYP, MP2, and CCSD(T) levels of theory by using quasirelativistic pseudopotentials for all atoms except fluorine and chlorine. All silver monohalides are stable molecules, while the relative stabilities of the subhalides, dihalides, and trihalides considerably decrease toward the larger halogens. The ground-state structure of all Ag(2)X silver subhalides has C(2)(v)() symmetry, and the molecules can be best described as [Ag(2)](+)X(-). Silver dihalides are linear molecules; AgF(2) has a (2)Sigma(g) ground state, while all of the other silver dihalides have a ground state of (2)Pi(g) symmetry. The potential energy surface (PES) of all silver trihalides has been investigated. Neither of these molecules has a D(3)(h)() symmetric trigonal planar geometry, due to their Jahn-Teller distortion. The minimum energy structure of AgF(3) is a T-shaped structure with C(2)(v)() symmetry. For AgCl(3), AgBr(3), and AgI(3), the global minimum is an L-shaped structure, which lies outside the Jahn-Teller PES. This structure can be considered as a donor-acceptor system, with X(2) acting as donor and AgX as acceptor. Thus, except for AgF(3), in the other three silver trihalides, silver is not present in the formal oxidation state 3.

Silver(I) Undecafluorodiantimonate(V)

The reaction between AgBF4 and excess of SbF5 in anhydrous hydrogen fluoride (aHF) yields the white solid AgSb2F11 after the solvent and the excess of SbF5 have been pumped off. Reaction between equimolar amounts of AgSb2F11 and AgBF4 yields AgSbF6. Meanwhile, oxidation of solvolyzed AgSb2F11 in aHF by elemental fluorine yields a clear blue solution of solvated Ag(II) cations and SbF6- anions. AgSb2F11 is orthorhombic, at 250 K, Pbca, with a=1091.80(7) pm, b=1246.28(8) pm, c=3880.2(3) pm, V=5.2797(6) nm3, and Z=24. The crystal structure of AgSb2F11 is related to the already known crystal structure of H3OSb2F11. Vibrational spectra of AgSb2F11 entirely match the literature-reported vibrational spectra of beta-Ag(SbF6)2, for which a formulation of a mixed-valence AgI/AgIII compound was suggested (AgIAgIII(SbF6)4). On the basis of obtained results it can be concluded that previously reported beta-Ag(SbF6)2 is in fact Ag(I) compound with composition AgSb2F11.

Xenon as a complex ligand: the tetra xenono Gold(II) cation in AuXe(4)2+(Sb(2)F(11)-)(2)

The first metal-xenon compound with direct gold-xenon bonds is achieved by reduction of AuF(3) with elemental xenon. The square planar AuXe(4)2+ cation is established by a single-crystal structure determination, with a gold-xenon bond length of approximately 274 picometers. The bonding between gold and xenon is of the final sigma donor type, resulting in a charge of approximately 0.4 per xenon atom.

Structural features of Ag[AuF4] and Ag[AuF6] and the stuctural relationship of Ag[AgF4]2 and Au[AuF4]2 to Ag[AuF4]2

Synchrotron radiation X-ray powder diffraction data (SPDD) have been obtained for Ag[AgF4]2, Au[AuF4]2, Ag[AuF4], and Ag[AuF6]. Ag[AgF4]2 and Au[AuF4]2 are isostructural with Ag[AuF4]2, space group (SG) P2(1)/n, Z = 2, with the following: for Ag[AgF4]2 a = 5.04664(8), b = 11.0542(2), c = 5.44914(9) A, beta = 97.170(2) degrees; for Au[AuF4]2 a = 5.203(2), b = 11.186(3), c = 5.531(2) A, beta = 90.55(2) degrees. The structure of Ag[AgF4]2 was refined successfully (SPDD) applying the Rietveld method, yielding the following interatomic distances (A): AgII-F = 2.056(12), 2.200(13), 2.558(13); AgIII-F = two at 1.846(12), others = 1.887(12), 1.909(13), 2.786-(12), 2.796(12), 2.855(12). AgAuF4, like other AA'F4 salts (A = Na-Rb; A' = Ag, Au), crystallizes in the KBrF4 structure type, SG I4/mcm (140), Z = 4 with a = 5.79109(6), c = 10.81676(7) A. SPDD gave (in A) four AuIII-F = 1.89(1) and eight AgI-F = 2.577(7). SPDD for AgAuF6 confirmed that it has the LiSbF6 structure, SG R3, Z = 3, with a = 5.2840(2), c = 15.0451(6) A.

Disproportionation of Ag(II) to Ag(I) and Ag(III) in Fluoride Systems and Syntheses and Structures of (AgF(+))(2)AgF(4)(-)MF(6)(-) Salts (M = As, Sb, Pt, Au, Ru)

Interaction of Ag(+) salts in anhydrous liquid hydrogen fluoride, aHF, with AgF(4)(-) salts gives amorphous red-brown diamagnetic Ag(I)Ag(III)F(4), which transforms exothermally to brown, paramagnetic, microcrystalline Ag(II)F(2) below 0 degrees C. Ag(I)Au(III)F(4) prepared from Ag(+) and AuF(4)(-) in aHF has a tetragonal unit cell and a KBrF(4) type lattice, with a = 5.788(1) Å, c = 10.806(2) Å, and Z = 4. Blue-green Ag(II)FAsF(6) disproportionates in aHF (in the absence of F(-) acceptors) to colorless Ag(I)AsF(6) and a black pseudotrifluoride, (Ag(II)F(+))(2)Ag(III)F(4)(-)AsF(6)(-). The latter and other (AgF)(2)AgF(4)MF(6) salts are also generated by oxidation of AgF(2) or AgF(+) salts in aHF with F(2) or in solutions of O(2)(+)MF(6)(-) salts (M = As, Sb, Pt, Au, Ru). Single crystals of (AgF)(2)AgF(4)AsF(6) were grown from an AgFAsF(6)/AsF(5) solution in aHF standing over AgF(2) or AgFBF(4), with F(2) as the oxidant. They are monoclinic, P2/c, at 20 degrees C, with a = 5.6045(6) Å, b = 5.2567(6) Å, c = 7.8061(8) Å, beta = 96.594(9) degrees, and Z = 1. The structure consists of (AgF)(n)()(n)()(+) chains (F-Ag-F = 180 degrees, Ag-F-Ag = 153.9(11) degrees, Ag-F = 2.003(4) Å), parallel to c, that enclose stacks of alternating AgF(4)(-) and AsF(6)(-), each anion making bridging contact with four Ag(II) cations of the four surrounding chains "caging" them. There is no registry between the ordered array in one "cage" and that in any neighboring "cage". The F-ligand anion bridges between the anions and, with the Ag(II) of the chains, generates a trifluoride-like structure. (AgF)(2)AgF(4)AsF(6) [like other (AgF)(n)()(n)()(+) salts] is a temperature-independent paramagnet except for a Curie "tail" below 50 K.

X-ray Crystallographic Studies of the Products of Oxidative Additions of Iodine to Cyclic Trinuclear Gold(I) Complexes: Directional Effects for Au-I.I-Au Interactions

The crystal structures of cyclic trinuclear organogold compounds, Au(3)I(n)()(CH(3)N=COCH(3))(3) (n = 2, 4, 6) reveal that pairs of iodine atoms are added successively to each of the gold atoms in the triangular complexes. Deep red needles of Au(3)I(6)(CH(3)N=COCH(3))(3).CH(2)Cl(2) crystallize in the monoclinic space group P2(1)/c, with a = 14.762(4) Å, b = 8.723(3) Å, c = 22.278(6) Å, and beta = 91.58(2) degrees at 123 K with Z = 4. Refinement of 6591 reflections and 164 parameters yielded R = 0.055. The structure consists of columns of the molecular units united by weak iodine.iodine interactions which range in length from 3.636(2) to 3.716(2) Å. Within the molecular unit, all iodine.iodine distances are well beyond the sum of their van der Waals radii and fall in the range from 3.965(2) to 4.211(2) Å. The gold coordination is significantly distorted from planarity with I-Au-I angles of ca. 163 degrees. In Au(3)I(6)(CH(3)N=COCH(3))(3) the intermolecular I.I interactions are significantly shorter than the intramolecular I.I contacts. Red parallelepipeds of the tetraiodo complex, Au(2)I(4)Au(CH(3)N=COCH(3))(3), crystallize in the triclinic space group P&onemacr;, with a = 7.404(2) Å, b = 9.278(2) Å, c = 16.331(3) Å, alpha = 80.77(3) degrees, beta = 78.68(3) degrees, and gamma = 81.85(3) degrees at 123 K with Z = 2. Refinement of 4963 reflections and 124 parameters yielded R = 0.048. No noteworthy intermolecular contacts are present in this compound. Orange-red hexagonal plates of the diiodo complex, AuI(2)Au(2)(CH(3)N=COCH(3))(3), crystallize in the monoclinic space group P2(1)/c, with a = 9.309(4) Å, b = 13.597(4) Å, c = 14.899(5) Å, and beta = 101.26(3) degrees at 123 K with Z = 4. Refinement of 4133 reflections and 121 parameters yielded R = 0.064. This structure consists of discrete molecular units displaying no noteworthy inter- or intramolecular contacts.