Diferrocenylmercury‐Bridged Diphosphine: A Chiral,Ambiphilic, and Redox‐Active Bidentate Ligand

A diphosphine chelate ligand with a wide and flexible bite angle, a unique stereochemical environment, and redox‐active and ambiphilic character is reported. Initially generated as its HgCl₂ complex by reaction of 1,2‐fc(PPh₂)(SnMe₃) (fc=ferrocenediyl) with HgCl₂ in acetone, treatment with [n‐Bu₄N]CN readily liberates the free chiral bidentate ligand. An intermolecular ClHg−Cl→Hgfc₂ (2.9929(13) Å) interaction that is unprecedented in ambiphilic ligand chemistry is seen in the solid structure of Hg(fcPPh₂)₂⋅HgCl₂ where the bridging mercury atom acts as a σ‐acceptor. Furthermore, a bis‐[Rh(COD)Cl] complex is introduced, which displays relatively short Rh⋅⋅⋅Hg contacts of 3.4765(5) and 3.4013(1) Å. Wiberg indices of 0.12 are determined for these Rh⋅⋅⋅Hg interactions and an AIM analysis reveals bond paths with an electron density ρ(r) of 1.2×10⁻² and 1.4×10⁻² e/a₀³ at the bond critical points.     

Dichloro­[(6R,7S,8S,14S)‐(–)‐sparteine‐κ2N,N′]mercury(II)

In the title compound, [HgCl₂(C₁₅H₂₆N₂)], the chiral alkaloid (6R,7S,8S,14S)‐(−)‐l ‐sparteine acts as a bident­ate ligand, with two Cl⁻ ligands occupying the remaining coordination sites, producing a distorted tetra­hedron. The N—Hg—N plane is twisted by 81.1 (2)° from the Cl—Hg—Cl plane. The mid‐point of the N⋯N line does not lie exactly on the Cl—Hg—Cl plane but is tilted towards one of the N atoms by 0.346 Å. Similarly, the mid‐point of the Cl⋯Cl line is tilted toward one of the Cl atoms by 0.163 Å. The packing structure shows that the complex is stabilized by two inter­atomic Cl⋯H contacts involving both Cl atoms and the methyl­ene or methine H atoms of the (−)‐sparteine ligand.     

A 1:2 complex of mercury(II) chloride with 1,3‐imidazole‐2‐thione

The Hg atom in the title monomeric complex, di­chloro­bis(3‐imidazolium‐2‐thiol­ato‐S)­mercury(II), [HgCl₂(C₃H₄N₂S)₂], is four‐coordinate having an irregular tetrahedral geometry composed of two Cl atoms [Hg—Cl 2.622 (2) and 2.663 (2) Å] and two thione S atoms [Hg—S 2.445 (2) and 2.462 (2) Å]. The monodentate thione ligand adopts a zwitterionic form and exists as the 3‐imidazolium‐2‐thiol­ate ion. The bond angle S1—Hg—S2 of 130.87 (8)° has the greatest deviation from ideal tetrahedral geometry. Intermolecular hydrogen bonds between two of the four N—H groups and one of the Cl atoms [3.232 (8) and 3.238 (7) Å] stabilize the crystal structure, while the other two N—H groups contribute through the formation of N—H?Cl intramolecular hydrogen bonds with the other Cl atom [3.121 (7) and 3.188 (7) Å].     

A Novel Dinuclear Nickel(II) Complex with Three Bridges of Cl–, OAc– and (‐OCH2CH2O‐) Group of N,N, N′, N′‐Tetrakis(2‐benzimidazolyl methyl‐1, 4‐di‐ethylene amino) Glycol Ether

The novel dinuclear Ni²⁺ complex [Ni₂(μ‐Cl)(μ‐OAc) (EGTB)]·Cl·ClO₄·2CH₃OH, where EGTB is N, N, N′, N′‐tetrakis (2‐benzimidazolyl methyl‐1, 4‐di‐ethylene amino)glycol ether, crystallizes in the orthorhombic space group Pnma with a = 15.272(2), b = 14.768(2), c = 22.486(3) Å, V = 5071.4(12) ų, Z = 4, D_calc = 1.414 g cm^?3, and is bridged by triply bridging agents of a chloride ion, an acetate and an intra‐ligand (‐OCH₂CH₂O‐) group. The nickel coordination geometry is that of a slightly distorted octahedron with a NiN₃O₂Cl arrangement of the ligand donor atoms. The Ni–Cl distance is 2.361(2) Å, and two Ni–O distances are 1.996(5) and 2.279(6) Å. The three Ni–N distances are 2.033(7), 2.060(6), and 2.166(6) Å with the Ni–N bond trans to an ether oxygen the shortest, the Ni–N bond trans to an acetate oxygen the middle and the Ni–N bond trans to Cl the longest.     

Internal Dynamics in Halogen‐Bonded Adducts: A Rotational Study of Chlorotrifluoromethane–Formaldehyde

The rotational spectra of two isotopologues of the 1:1 complex between chlorotrifluoromethane and formaldehyde have been recorded and analyzed by using Fourier‐transform microwave spectroscopy. Only one rotamer was detected, with the two constituent molecules held together through a Cl???O halogen bond (R_Cl???O=3.048 Å). The dimer displays two simultaneous large‐amplitude intramolecular motions. The internal rotation of formaldehyde around its symmetry axis (V₂=28(5) cm^?1) splits all the rotational transitions into two component lines with a relative intensity ratio of 1:3. On the other hand, the almost free internal rotation (V₃≈2.5 cm^?1) of the CF₃ symmetric top increases the “rigid” value of the rotational constant A by almost one order of magnitude. In addition, all the transitions display a hyperfine structure due to the ³⁵Cl (or ³⁷Cl) nucleus quadrupole effects.     

Chloromethane–Water Adduct: Rotational Spectrum,Weak Hydrogen Bonds,and Internal Dynamics

The rotational spectra of four isotopologues of the 1:1 complex between chloromethane and water revealed the presence of only one rotamer in a pulsed jet expansion. The two subunits are linked through two weak hydrogen bonds, O? H???Cl (R_H???Cl=2.638(2) Å) and C? H???O (R_H???O=2.501(2) Å), forming a five‐membered ring. All transitions display the hyperfine structure due to the ³⁵Cl (or ³⁷Cl) nuclear quadrupole effects. Dynamical features in the spectrum are caused by two large‐amplitude motions. Each component line appears as an asymmetric doublet with a relative intensity ratio of 1:3. The splittings led to the determination of barrier to internal rotation of water around its symmetry axis, V₂=320(10) cm^?1. Finally, an unexpected small value of the inertial defect (?0.96 uŲ rather than ?3.22 uŲ) allowed the estimation of the barrier to the internal rotation of the CH₃ group, V₃≈8 cm^?1.     

A New Conformation With an Extraordinarily Long, 3.04 Å Two‐Electron,Six‐Center Bond Observed for the π‐[TCNE]22− Dimer in [NMe4]2[TCNE]2 (TCNE=Tetracyanoethylene)

[NMe₄]₂[TCNE]₂ (TCNE=tetracyanoethenide) formed from the reaction of TCNE and (NMe₄)CN in MeCN has ν_CN IR absorptions at 2195, 2191, 2172, and 2156 cm^?1 and a ν_CC absorption at 1383 cm^?1 that are characteristic of reduced TCNE. The TCNEs have an average central C?C distance of 1.423 Å that is also characteristic of reduced TCNE. The reduced TCNE forms a previously unknown non‐eclipsed, centrosymmetric π‐[TCNE]₂^2? dimer with nominal C₂ symmetry, 12 sub van der Waals interatomic contacts <3.3 Å, a central intradimer separation of 3.039(3) Å, and comparable intradimer C???N distances of 3.050(3) and 2.984(3) Å. The two pairs of central C???C atoms form a ?C?C???C?C of 112.6° that is substantially greater than the 0° observed for the eclipsed D_2h π‐[TCNE]₂^2? dimer possessing a two‐electron, four‐center (2e^?/4c) bond with two C???C components from a molecular orbital (MO) analysis. A MO study combining CAS(2,2)/MRMP2/cc‐pVTZ and atoms‐in‐molecules (AIM) calculations indicates that the non‐eclipsed, C₂ π‐[TCNE]₂^2? dimer exhibits a new type of a long, intradimer bond involving one strong C???C and two weak C???N components, that is, a 2e^?/6c bond. The C₂ π‐[TCNE]₂^2? conformer has a singlet, diamagnetic ground state with a thermally populated triplet excited state with J/k_B=1000 K (700 cm^?1; 86.8 meV; 2.00 kcal mol^?1; H=?2 JS_a?S_b); at the CAS(2,2)/MBMP2 level the triplet is computed to be 9.0 kcal mol^?1 higher in energy than the closed‐shell singlet ground state. The results from CAS(2,2)/NEVPT2/cc‐pVTZ calculations indicate that the C₂ and D_2h conformers have two different local metastable minima with the C₂ conformer being 1.3 kcal mol^?1 less stable. The different natures of the C₂ and D_2h conformers are also noted from the results of valence bond (VB) qualitative diagram that shows a 10e^?/6c bond with one C???C and two C???N bonding components for the C₂ conformer as compared to the 6e^?/4c bond for the D_2h conformer with two C???C bonding components.     

Synthesis,Spectroscopic, and X‐Ray Diffraction Studies of cis‐Dichlorobis(4‐propanoyl‐2,4‐dihydro‐5‐methyl‐2‐phenyl3 H‐pyrazol‐3‐onato) Tin(IV)

Reaction between an aqueous ethanol solution of tin(II) chloride and that of 4‐propanoyl‐2,4‐dihydro‐5‐methyl‐2‐phenyl‐3 H‐pyrazol‐3‐one in the presence of O₂ gave the compound cis‐dichlorobis(4‐propanoyl‐2,4‐dihydro‐5‐methyl‐2‐phenyl‐3 H‐pyrazol‐3‐onato) tin(IV) [(C₂₆H₂₆N₄O₄)SnCl₂]. The compound has a six‐coordinated Sn^IV centre in a distorted octahedral configuration with two chloro ligands in cis position. The tin atom is also at a pseudo two‐fold axis of inversion for both the ligand anions and the two cis‐chloro ligands. The orange compound crystallizes in the triclinic space group P 1 with unit cell dimensions, a = 8.741(3) Å, b = 12.325(7) Å, c = 13.922(7) Å; α = 71.59(4), β = 79.39(3), γ = 75.18(4); Z = 2 and D_x = 1.575 g cm^–3. The important bond distances in the chelate ring are Sn–O [2.041 to 2.103 Å], Sn–Cl [2.347 to 2.351 Å], C–O [1.261 to 1.289 Å] and C–C [1.401 Å] the bond angles are O–Sn–O 82.6 to 87.7° and Cl–Sn–Cl 97.59°. The UV, IR, ¹H NMR and ¹¹⁹Sn Mössbauer spectral data of the compound are reported and discussed.     

{μ‐PbSe}: A Heavy CO Homologue as an Unexpected Ligand

Reactions of [K(18‐crown‐6)]₂[Pb₂Se₃] and [K([2.2.2]crypt)]₂[Pb₂Se₃] with [Rh(PPh₃)₃Cl] in en (ethane‐1,2‐diamine) afforded ionic compounds with [Rh₃(PPh₃)₆(μ₃‐Se)₂]^? and [Rh₃(CN)₂(PPh₃)₄(μ₃‐Se)₂(μ‐PbSe)]^3? anions, respectively. The latter contains a PbSe ligand, a rather uncommon homologue of CO that acts as a μ‐bridge between two Rh atoms. Quantum chemical calculations yield a significantly higher bond energy for PbSe than for CO, since the size of the ligand orbitals better matches the comparably rigid Rh‐Se‐Rh angles and the resulting Rh???Rh distance. To rationalize the bent coordination of the ligand, orbitals with significant ligand contributions and their dependence on the bonding angle were investigated in detail.     

Kristallzucht und Strukturverfeinerung von Quecksilber(II)‐amidchlorid – HgClNH2

Crystal Growth and Refinement of the Crystal Structure of Mercury(II) Amide Chloride – HgClNH₂ Single crystals were prepared by recrystallization of HgClNH₂ from aqueous NH₃/NH₄⁺ solution at 160 °C. They were used for a single‐crystal X‐ray structure redetermination. The previously reported [W. N. Lipscomb, Acta. Crystallogr. 1951 , 4, 266.] structural topology determined on basis of X‐ray powder diffraction data is now confirmed. However, a higher symmetry is found: Space group type Pmma (instead of Pmm2), a = 6.709(1) Å, b = 4.351(1) Å, c = 5.154(1) Å, Z = 2. The crystal structure contains zig‐zag‐chains [Hg(NH₂)_2/2]⁺. Four Cl atoms complete the coordination sphere of Hg to a distorted octahedron. These share common faces and edges in layers [HgCl_4/4(NH₂)_2/2]. These layers are connected via hydrogen bonds N–H…Cl.     

31P-NMR and X-Ray Studies of the Complexes [HgX2 (1)]. (1=2, 11-bis (diphenylphosphinomethyl)benzo [c]phenanthrene,X=Cl,I)

The ³¹P{¹H}-NMR characteristics of the complexes [HgX₂( 1 )] and [HgX₂-(PPh₂Bz)₂] (X = NO₃, Cl, Br, I, SCN, CN) and the solid state structures of the complexes [HgCl₂( 1 )] and [HgI₂( 1 )] ( 1 = 2,11-bis (diphenylphosphinomethyl)benzo-[c]phenanthrene) have been determined. The ¹J(¹⁹⁹Hg, ³¹P) values increase in the order CN < I < SCN < Br < Cl < NO₃. The two molecular structures show a distorted tetrahedral geometry about mercury. Pertinent bond lengths and bond angles from the X-ray analysis are as follows: Hg? P = 2.485(7) Å and 2.509 (8) Å, Hg? Cl = 2.525 (8) Å and 2.505 (10) Å, P? Hg? P = 125.6(3)°, Cl? Hg? Cl = 97.0(3)° for [HgCl₂( 1 )] and Hg? P = 2.491 (10) Å and 2.500(11) Å, Hg? I = 2.858(5) Å and 2.832(3) Å, P? Hg? P = 146.0(4)°, I? Hg? I = 116.9(1)° for [HgI₂( 1 )]. The equation, derived previously, relating ¹J(¹⁹⁹Hg, ³¹P) and the angles P? Hg? P and X? Hg? X is shown to be valid for 1 .     

Novel isolated,L‐amino acid‐ligated rhodium catalysts that induce highly helix‐sense‐selective polymerization of an achiral 3,4,5‐trisubstituted phenylacetylene

Two novel chiral well‐defined rhodium complexes, Rh(cod)(L‐Phe) (cod = 1,5‐cyclooctadiene, Phe = phenylalanine) and Rh(cod)(L‐Val) (Val = valine) were synthesized, isolated by recrystallization, and characterized. The helix‐sense‐selective polymerization (HSSP) of an achiral 3,4,5‐trisubstituted phenylacetylene, p‐dodecyloxy‐m,m‐dihydroxyphenylacetylene (DoDHPA) was examined by using the two Rh complexes as catalysts. These catalysts provided high molecular weight polymers (M_w 28 × 10⁴?45 × 10⁴) in about 40%–85% yields. The resulting polymers exhibited a bisignated CD signal at about 300 nm and a broad signal around 470 nm, indicating that they have preferential one‐handed helical structure. The present catalysts achieved larger molar ellipticity up to [θ]₃₁₀ = 13.0 × 10⁴ deg cm²/dmol than those with binary chiral catalytic systems, [Rh(cod)Cl]₂/(L‐phenylalaninol), [Rh(cod)Cl]₂/(L‐valinol), and [Rh(nbd)Cl]₂/(R)‐PEA. All these results manifest that the present, well‐defined Rh complexes serve as excellent catalysts for the HSSP of DoDHPA. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2346–2351     

Solvent–metal interactions in bis[1,2‐dicarba‐closo‐dodecaboran(12)‐1‐yl]mercury(II) dichloromethane solvate and bis[1,12‐dicarba‐closo‐dodecaboran(12)‐1‐yl]mercury(II) tetrahydrofuran solvate

The title compounds, bis­[1,2‐dicarba‐closo‐dodecaboran(12)‐1‐yl]­mercury(II) di­chloro­methane solvate, [Hg(C₂B₁₀H₁₁)₂]·CH₂Cl₂, (I), and bis­[1,12‐dicarba‐closo‐dodecaboran(12)‐1‐yl]­mercury(II) tetra­hydro­furan solvate, [Hg(C₂B₁₀H₁₁)₂]·C₄H₈O, (II), were prepared in excellent yields using a robust synthetic procedure involving the reaction of HgCl₂ with the appropriate monoli­thiocarborane. X‐Ray analysis of the products revealed strong interactions between the Hg atoms in both complexes and the respective lattice solvent. The distances between the Hg^II centers and the Cl atoms of the dichloromethane solvent molecule in the ortho‐carborane derivative, (I), and the O atom of the tetra­hydro­furan molecule in the para‐carborane complex, (II), are shorter than the sums of the van der Waals radii for Hg and Cl (3.53 Å), and Hg and O (3.13 Å), respectively, indicating moderately strong interactions. There are two crystallographically independent mol­ecules in the asymmetric unit of both compounds, which, in each case, are related by differing relative positions of the cages.     

The dinuclear scandium(III) cyclooctatetraenyl chloride complex di‐μ‐chlorido‐bis[(η8‐cyclooctatetraene)(tetrahydrofuran‐κO)scandium(III)]

Only a few cyclooctatetraene dianion (COT) π‐complexes of lanthanides have been crystallographically characterized. This first single‐crystal X‐ray diffraction characterization of a scandium(III) COT chloride complex, namely di‐μ‐chlorido‐bis[(η⁸‐cyclooctatetraene)(tetrahydrofuran‐κO )scandium(III)], [Sc₂(C₈H₈)₂Cl₂(C₄H₈O)₂] or [Sc(COT)Cl(THF)]₂ (THF is tetrahydrofuran), (1), reveals a dimeric molecular structure with symmetric chloride bridges [average Sc—Cl = 2.5972 (7) Å] and a η⁸‐bound COT ligand. The COT ring is planar, with an average C—C bond length of 1.399 (3) Å. The Sc—C bond lengths range from 2.417 (2) to 2.438 (2) Å [average 2.427 (2) Å]. Direct comparison of (1) with the known lanthanide (Ln) analogues (La, Ce, Pr, Nd, and Sm) illustrates the effect of metal‐ion (M ) size on molecular structure. Overall, the M —Cl, M —O, and M —C bond lengths in (1) are the shortest in the series. In addition, only one THF molecule completes the coordination environment of the small Sc^III ion, in contrast to the previously reported dinuclear Ln–COT–Cl complexes, which all have two bound THF molecules per metal atom.     

Strong N−X⋅⋅⋅O−N Halogen Bonds: A Comprehensive Study on N‐Halosaccharin Pyridine N‐Oxide Complexes

A study of the strong N?X???^?O?N⁺ (X=I, Br) halogen bonding interactions reports 2×27 donor×acceptor complexes of N‐halosaccharins and pyridine N‐oxides (PyNO). DFT calculations were used to investigate the X???O halogen bond (XB) interaction energies in 54 complexes. A simplified computationally fast electrostatic model was developed for predicting the X???O XBs. The XB interaction energies vary from ?47.5 to ?120.3 kJ mol^?1; the strongest N?I???^?O?N⁺ XBs approaching those of 3‐center‐4‐electron [N?I?N]⁺ halogen‐bonded systems (ca. 160 kJ mol^?1). ¹H NMR association constants (K_XB) determined in CDCl₃ and [D₆]acetone vary from 2.0×10⁰ to >10⁸ m ^?1 and correlate well with the calculated donor×acceptor complexation enthalpies found between ?38.4 and ?77.5 kJ mol^?1. In X‐ray crystal structures, the N‐iodosaccharin‐PyNO complexes manifest short interaction ratios (R_XB) between 0.65–0.67 for the N?I???^?O?N⁺ halogen bond.     

Bis(N,N′‐dimethylimidazol‐2‐yl­idene)mercury chlorotriiodo­mercury dimethyl sulfoxide solvate

The double mercury salt [Hg(C₅H₈N₂)₂][HgClI₃]·C₂H₆OS was prepared and its structure characterized. The [Hg(C₅H₈N₂)₂]²⁺ cation lies about an inversion centre and the [HgClI₃]^2? anion lies on a mirror plane. Cations and anions are linked to form a one‐dimensional polymer by weak Hg?Cl interactions [Hg?Cl 3.3744 (3) Å]. The mercury–carbene bond distance [2.076 (7) Å] is typical of a dicationic mercury–carbene species.     

Synthesis and molecular structure of Cr(salen)(μ‐N)RhCl(COD): the first example of a heterobimetallic nitride‐bridged complex containing chromium

Five‐coordinate Cr(N)(salen) {salen is 2,2′‐[ethane‐1,2‐diylbis(nitrilomethylidyne)]diphenolate} reacts with [RhCl(COD)]₂ (COD is 1,5‐cyclooctadiene) to yield the heterobimetallic nitride‐bridged title compound, namely chlorido‐2κCl‐[2(η⁴)‐1,5‐cyclooctadiene]{2,2′‐[ethane‐1,2‐diylbis(nitrilomethylidyne)]diphenolato‐1κ⁴O,N,N′,O′}‐μ‐nitrido‐1:2κ²N:N‐chromium(V)rhodium(I), [CrRh(C₁₆H₁₄N₂O₂)ClN(C₈H₁₂)]. The Cr—N bond of 1.5936 (14) Å is elongated by only 0.035 Å compared to the terminal Cr—N bond in the precursor. The nitride bridge is close to being linear [173.03 (9)°] and the Rh—N bond of 1.9594 (14) Å is very short for a monodentate nitrogen‐donor ligand, indicating significant π‐acceptor character of the Cr[triple‐bond]N group.     

Halide Abstraction by Na[B{C6H3(CF3)2‐3,5}4]: Synthesis and Structural Characterization of the Rhodium(I) Cations [(η6‐arene)Rh(PPh3)2]+ (Arene = benzene,toluene)

Halide abstraction from [(Ph₃P)₂Rh(μ‐Cl)]₂ by the sodium salt of the weakly coordinating [BAr^f₄]^? anion [Ar^f = C₆H₃(CF₃)₂‐3,5] in the presence of excess arene offers a convenient, high‐yielding route to the half‐sandwich cations [(arene)Rh(PPh₃)₂]⁺[BAr^f₄]^? [arene = benzene ( 1 ), toluene ( 2 )]. Crystalline samples of 1 and 2 are isomorphous [a = 13.1270(2), b = 15.3030(2), c = 17.5760(3) Å, α = 74.620(1), β = 81.533(1), γ = 88.540(1)° for 1 ] and feature the arene ligand bound to the rhodium atom in η⁶ fashion.     

Nitridorhenium(V) Complexes with 1,3,4‐Triphenyl‐1,2,4‐triazol‐5‐ylidene

[ReNCl₂(PPh₃)₂] and [ReNCl₂(PMe₂Ph)₃] react with the N‐heterocyclic carbene (NHC) 1,3,4‐triphenyl‐1,2,4‐triazol‐5‐ylidene (HL^Ph) under formation of the stable rhenium(V) nitrido complex [ReNCl(HL^Ph)(L^Ph)], which contains one of the two NHC ligands with an additional orthometallation. The rhenium atom in the product is five‐coordinate with a distorted square‐pyramidal coordination sphere. The position trans to the nitrido ligand is blocked by one phenyl ring of the monodentate HL^Ph ligand. The Re–C(carbene) bond lengths of 2.072(6) and 2.074(6) Å are comparably long and indicate mainly σ‐bonding between the NHC ligand and the electron deficient d² metal atom. The chloro ligand in [ReNCl(HL^Ph)(L^Ph)] is labile and can be replaced by ligands such as pseudohalides or monoanionic thiolates such as diphenyldithiophosphinate (Ph₂PS₂^?) or pyridine‐2‐thiolate (pyS^?). X‐ray structure analyses of [ReN(CN)(HL^Ph)(L^Ph)] and [ReN(pyS)(HL^Ph)(L^Ph)] show that the bonding situation of the NHC ligands (Re–C(carbene) distances between 2.086(3) and 2.130(3) Å) in the product is not significantly influenced by the ligand exchange. The potentially bidentate pyS^? ligand is solely coordinated via its thiolato functionality. Hydrogen atoms of each one of the phenyl rings come close to the unoccupied sixth coordination positions of the rhenium atoms in the solid state structures of all complexes. Re–H distances between 2.620 and 2.712Å do not allow to discuss bonding, but with respect to the strong trans labilising influence of “N^3?”, weak interactions are indicated.     

Resonance Character of Copper/Silver/Gold Bonding in Small Molecule⋅⋅⋅MX (X=F,Cl, Br,CH3, CF3) Complexes

The resonance character of Cu/Ag/Au bonding is investigated in B???M?X (M=Cu, Ag, Au; X=F, Cl, Br, CH₃, CF₃; B=CO, H₂O, H₂S, C₂H₂, C₂H₄) complexes. The natural bond orbital/natural resonance theory results strongly support the general resonance‐type three‐center/four‐electron (3c/4e) picture of Cu/Ag/Au bonding, B:M?X?B⁺?M:X^?, which mainly arises from hyperconjugation interactions. On the basis of such resonance‐type bonding mechanisms, the ligand effects in the more strongly bound OC???M?X series are analyzed, and distinct competition between CO and the axial ligand X is observed. This competitive bonding picture directly explains why CO in OC???Au?CF₃ can be readily replaced by a number of other ligands. Additionally, conservation of the bond order indicates that the idealized relationship b_B???M+b_MX=1 should be suitably generalized for intermolecular bonding, especially if there is additional partial multiple bonding at one end of the 3c/4e hyperbonded triad.