Search

Hericene is an unusual hexaolefin consisting of three 1,3-diene units located on a rigid bicyclo [2.2.2]octane framework that restricts the geometrical relationships of metal atoms bonded to these olefinic units. In order to explore possible effects of this rigidity limiting metal–metal interaction in polynuclear derivatives possibly stabilizing coordinatively unsaturated species, the structures and energetics of the hericene iron carbonyl complexes (hericene)Fem(CO)n (m = 1, n = 3; m = 2, n = 6, 5; m = 3, n = 9, 8) have been investigated by density functional theory. The lowest-energy (hericene)Fem(CO)3m (m = 1, 2, 3) structures have the cavities of the hericene ligand filled with a single Fe(CO)3 moiety bonded to a 1,3-diolefin unit. Such species have been synthesized by the reaction of Fe2(CO)9 with hericene. For the (hericene)Fe2(CO)5 system, the lowest energy structures are singlet structures with an Fe(CO)3 unit bonded to a 1,3-diene unit in one hericene cavity and an Fe(CO)2 unit in another hericene cavity bonded to three C=C double bonds from two 1,3-diene units. Higher energy (hericene)Fe2(CO)5 structures include a structure in which a single hericene cavity contains a Fe2(CO)4(µ-CO) moiety with each iron atom bonded to a 1,3-diene unit. In addition, both singlet and triplet (hericene)Fe2(CO)5 structures are found in which an Fe(CO)3 moiety and an Fe(CO)2 moiety located in separate hericene cavities are each bonded to a 1,3-diene unit. The lowest-energy (hericene)Fe3(CO)8 structures have two hericene cavities containing Fe(CO)3 moieties fully bonded to 1,3-diene units and a third hericene cavity containing an Fe(CO)2 moiety fully bonded to a 1,3-diene unit.

Trinuclear and tetranuclear ruthenium carbonyls of the types Ru3(CO)n(NO)2, Ru3(N)(CO)n(NO), Ru3(N)2(CO)n, Ru3(N)(CO)n(NCO), Ru3(CO)n(NCO)(NO), Ru4(N)(CO)n(NO), Ru4(N)(CO)n(NCO), and Ru4(N)2(CO)n related to species observed experimentally in the chemistry of Ru3(CO)10(µ-NO)2 have been investigated using density functional theory. In all cases, the experimentally observed structures have been found to be low-energy structures. The low-energy trinuclear structures typically have a central strongly bent Ru–Ru–Ru chain with terminal CO groups and bridging nitrosyl, isocyanate, and/or nitride ligands across the end of the chain. The low-energy tetranuclear structures typically have a central Ru4N unit with terminal CO groups and a non-bonded pair of ruthenium atoms bridged by a nitrosyl or isocyanate group.

Three different pathways for the atomic iodine plus water trimer reaction I + (H2O)3 → HI + (H2O)2OH were preliminarily examined by the DFT-MPW1K method. Related to previous predictions for the F/Cl/Br + (H2O)3 reactions, three pathways for the I + (H2O)3 reaction are linked in terms of geometry and energetics. To legitimize the results, the “gold standard” CCSD(T) method was employed to investigate the lowest-lying pathway with the correlation-consistent polarized valence basis set up to cc-pVQZ(-PP). According to the CCSD(T)/cc-pVQZ(-PP)//CCSD(T)/cc-pVTZ(-PP) results, the I + (H2O)3 → HI + (H2O)2OH reaction is predicted to be endothermic by 47.0 kcal mol−1. The submerged transition state is predicted to lie 43.7 kcal mol−1 above the separated reactants. The I···(H2O)3 entrance complex lies below the separated reactants by 4.1 kcal mol−1, and spin-orbit coupling has a significant impact on this dissociation energy. The HI···(H2O)2OH exit complex is bound by 4.3 kcal mol−1 in relation to the separated products. Compared with simpler I + (H2O)2 and I + H2O reactions, the I + (H2O)3 reaction is energetically between them in general. It is speculated that the reaction between the iodine atom and the larger water clusters may be energetically analogous to the I + (H2O)3 reaction. The iodine reaction I + (H2O)3 is connected with the analogous valence isoelectronic bromine/chlorine reactions Br/Cl + (H2O)3 but much different from the F + (H2O)3 reaction. Significant difference with other halogen systems, especially for barrier heights, are seen for the iodine systems.

The geometries, energetics, and preferred spin states of the second-row transition metal tris(butadiene) complexes (C4H6)3M (M = Zr–Pd) and their isomers, including the experimentally known very stable molybdenum derivative (C4H6)3Mo, have been examined by density functional theory. Such low-energy structures are found to have low-spin singlet and doublet spin states in contrast to the corresponding derivatives of the first-row transition metals. The three butadiene ligands in the lowest-energy (C4H6)3M structures of the late second-row transition metals couple to form a C12H18 ligand that binds to the central metal atom as a hexahapto ligand for M = Pd but as an octahapto ligand for M = Rh and Ru. However, the lowest-energy (C4H6)3M structures of the early transition metals have three separate tetrahapto butadiene ligands for M = Zr, Nb, and Mo or two tetrahapto butadiene ligands and one dihapto butadiene ligand for M = Tc. The low energy of the experimentally known singlet (C4H6)3Mo structure contrasts with the very high energy of its experimentally unknown singlet chromium (C4H6)3Cr analog relative to quintet (C12H18)Cr isomers with an open-chain C12H18 ligand.

The article reflects on the contribution of professor Henry F. Schaefer III to the quantum chemistry. It views that he has made contributions to several electronic-structure methods and chemical systems. It opines that he has groomed more than 80 Ph.D. students, 50 undergraduates and dozens of postdoctoral associates through his group.

Article title: The heavy Carbene analogues SbH2+ and BiH2+. Convergent quantum mechanical studies*Authors: Jincan Jin, Henry F. Mull, Justin M. Turney and Henry F. Schaefer IIIJournal:Molecular PhysicsDOI:https://doi.org/10.1080/00268976.2023.2271579When the article was first published online, there were few grammatical corrections in abstract, introduction and section 3.1 and enthalpy value corrections in section 3.2.These are now corrected and republished both online and print. [Extracted from the article]

The cobalt carbonyl nitrosyls Co(NO)(CO)n(n= 4, 3, 2, 1) and Co2(NO)2(CO)n(n= 5, 4, 3, 2) have been studied by density functional theory. The lowest energy structures for the mononuclear derivatives Co(NO)(CO)n(n= 3, 2, 1) parallel those of the corresponding isoelectronic Ni(CO)n+1derivatives. In addition, a thermodynamically unstable Co(NO)(CO)4structure is predicted with a bent nitrosyl group. The potential energy surfaces of the binuclear cobalt carbonyl nitrosyl derivatives Co2(NO)2(CO)n(n= 5, 4, 3, 2) are complicated by the similar energies of analogous structures with bridging carbonyl or bridging nitrosyl groups. However, these structures are analogous to those previously predicted for the isoelectronic binuclear nickel carbonyls Ni2(CO)n+2. Thus the lowest energy structures of Co2(NO)2(CO)5, Co2(NO)2(CO)4, and Co2(NO)2(CO)3have one, two, and three bridging groups, respectively, just like the isoelectronic Ni2(CO)n+2. For Co2(NO)2(CO)5and Co2(NO)2(CO)4the otherwise analogous structures with bridging carbonyl and/or nitrosyl groups are of very similar energies. However, for Co2(NO)2(CO)3there appears to be a particularly stable triply carbonyl bridged structure with an unusually short CoCo distance consistent with the formal triple bond required to give the cobalt atoms the favored 18-electron configuration. [ABSTRACT FROM AUTHOR]

For the saturated carbonyl trimer Ru3(CO)12theoretical methods predict a doubly bridged Ru3(CO)10(μ-CO)2structure to lie only 0.3 kcal mol−1above the unbridged global minimum in accord with the fluxional properties observed experimentally by carbon-13 NMR on the very stable unbridged Ru3(CO)12. For M3(CO)11and M3(CO)10the global minima for the Fe, Ru, and Os derivatives each have totally different arrangements of the carbonyl groups. Thus the global minimum of Ru3(CO)11is singly edge-semibridged Ru3(CO)10(μ-CO) in contrast to the doubly face-bridged Fe3(CO)9(μ3-CO)2and triply edge-bridged Os3(CO)8(μ-CO)3found as global minima for the iron and osmium analogues, respectively. Furthermore, comparison of our predicted ν(CO) frequencies for low-lying unbridged, singly bridged, and doubly bridged isomers of Ru3(CO)11with the 1987 experiments of Bentsen and Wrighton indicates that three different Ru3(CO)11isomers are generated in these low-temperature inert matrix Ru3(CO)12photolysis experiments depending on the conditions. For Ru3(CO)10the global minimum is a triply bridged structure Ru3(CO)7(μ-CO)3, which is very different from the Fe3(CO)9(μ3-CO) and Os3(CO)8(μ3-CO)(μ-CO) global minima found for the iron and osmium analogues, respectively. For Ru3(CO)9the global minimum is a singly bridged structure Ru3(CO)8(μ-CO) analogous to the global minimum for the osmium analogue but totally different from the triply bridged global minimum of Fe3(CO)9. [ABSTRACT FROM AUTHOR]

The equilibrium geometries, thermochemistry, and vibrational frequencies of the homoleptic binuclear rhenium carbonyls Re2(CO)n (n = 10, 9, 8, 7) were determined using the MPW1PW91 and BP86 methods from density functional theory (DFT) with the effective core potential basis sets LANL2DZ and SDD. In all cases triplet structures for Re2(CO)n were found to be unfavorable energetically relative to singlet structures, in contrast to corresponding Mn2(CO)n derivatives, apparently owing to the larger ligand field splitting of rhenium. For M2(CO)10 (M = Mn, Re) the unbridged structures (OC)5M–M(CO)5 are preferred energetically over structures with bridging CO groups. For M2(CO)9 (M = Mn, Re) the two low energy structures are (OC)4M(μ-CO)M(CO)4 with an M–M single bond and a four-electron donor bridging CO group and (OC)4MM(CO)5 with no bridging CO groups and an MM distance suggesting a double bond. The lowest energy structures for Re2(CO)8 have ReRe distances in the range 2.6–2.7 Å suggesting the triple bonds required to give the Re atoms the favored 18-electron configuration. Low energy structures for Re2(CO)7 are either of the type (OC)4MM(CO)3 with short metal–metal distances suggesting triple bonds or have a single four-electron donor bridging CO group and longer M–M distances consistent with single or double bonds. The 18-electron rule thus appears to be violated in these highly unsaturated Re2(CO)7 structures. [ABSTRACT FROM AUTHOR]

The structures of the tetranuclear osmium carbonyl derivatives Os4(CO)n (n = 16, 15, 14, 13, 12) have been investigated using the density functional theory method MPW1PW91 with the SDD effective core potential basis set, found to be effective in previous work for the study of Os3(CO)12. The Os4 clusters in the lowest energy structures for Os4(CO)16, Os4(CO)15, and Os4(CO)14 are found to be rhombi, butterflies, and tetrahedra with four, five, and six Os–Os bonds, respectively, in accord with structures determined by X-ray diffraction as well as the 18-electron rule. The fluxionality of tetrahedral Os4(CO)14, suggested by experimental work of Johnston, Einstein, and Pomeroy, is confirmed by our DFT studies, which find four Os4(CO)14 structures within 1.5 kcal mol−1 of each other with similar tetrahedral Os4 frameworks but with different arrangements of bridging and semibridging carbonyl groups. The lowest energy structures for the more unsaturated Os4(CO)13 and Os4(CO)12 are also based on Os4 tetrahedra but with shorter Os–Os edge lengths than in Os4(CO)14 suggesting delocalized multiple bonding in the more highly unsaturated systems. Thus the global minimum for Os4(CO)12 is predicted to have tetrahedral symmetry, with all terminal carbonyl groups analogous to the experimentally known structure of (µ3-H)4Re3(CO)12, but without the face-bridging hydrogen atoms. [ABSTRACT FROM AUTHOR]

The synthesis and structure of a Zn–Zn-bonded compound supported by a doubly reduced α-diimine ligand, [Na(THF)2]2·[LZn–ZnL] (L = [(2,6-iPr2C6H3)N(Me)C]22−) are reported, with a Zn–Zn bond length of 2.399(1) Å. [ABSTRACT FROM AUTHOR]

Neutral bis(pentalene)metal sandwich compounds have been synthesized for the first row transition metals titanium and iron. In this connection, the complete series of first row transition metal bis(pentalene)metal complexes (C8H6)2M (M = Ti, V, Cr, Mn, Fe, Co, Ni) has now been investigated by density functional theory in order to evaluate the effect of the metal electronic requirements on the hapticity of the pentalene ligands. The lowest energy structure for the titanium complex is the 18-electron complex (η8-C8H6)(η6-C8H6)Ti with one octahapto and one hexahapto pentalene ligand rather than the previously suggested 20-electron complex (η8-C8H6)2Ti with two octahapto pentalene ligands. The experimental NMR observations on (C8H6)2Ti can then be reinterpreted as interchange of octahapto and hexahapto bonding of the pentalene units through a low energy bis(octahapto) (η8-C8H6)2Ti transition state. The lowest energy structure for (C8H6)2V has two fulvene-like hexahapto pentalene ligands and a local vanadium environment similar to the well-known dibenzenevanadium. The lowest energy structures of the later first row transition metals have two pentahapto pentalene ligands with local metal environments similar to those in the corresponding metallocenes. In the manganese and iron structures of this type, the remaining unpaired electrons on one of the uncomplexed carbon atoms in each η5-C8H6system form a C–C single bond to couple the two pentalene ligands. This coupling of the two pentalene systems through a C–C single bond is similar to that found experimentally by X-ray crystallography in bis(pentalene)iron, (η5-C8H6)2Fe. [ABSTRACT FROM AUTHOR]

Recently synthesized by the group of Sadler, the platinum(iv) diazido complexes [Pt(N3)2(OH)2(L′)(L′′)] (L′ and L′′ are N-donor ligands) have potential to be used as photoactivatable metallodrugs in cancer chemotherapy. In the present study optimized structures and UV-Vis electronic spectra of trans,trans,trans- and cis,trans,cis-[Pt(N3)2(OH)2(NH3)2] (1tand 1c, respectively) as well as cis,trans,cis-[Pt(N3)2(OH)2(L)2] (L = NH3, NH2CH3, NF3, PH3, PF3, H2O, CO, OH−, CN−, py, imid; 2c–11c) and cis,trans-[Pt(N3)2(OH)2(bpy)] (12c) complexes were predicted using density functional theory (DFT). The ground state electronic structures of all complexes were analyzed with the help of the natural bond orbital analysis (NBO). The electronic spectra of 1cand 1twere computed using time-dependent density functional theory (TDDFT) with five different density functionals and the ab initioCASSCF/CASPT2 method (for the five lowest energy transitions). The best agreement with available experiments was found in the case of the long-range corrected ωB97X functional. The electronic transitions were characterized by the analysis of the natural transition orbitals (NTO). The low-lying excited singlet states of 1tand 1chave significant azide-to-platinum(iv) charge-transfer character (LMCT). Geometry optimization of the three lowest singlet excited states performed using TDDFT results in the simultaneous dissociation of two azide ligands with the formation of the azidyl radicals N3 and photoreduction of PtIVto PtII. Variation of the ligand L does not strongly affect the nature and the relative energies of the low-lying states. It is shown that the replacement of the OH−groups in 1cby OPh−ligands results in the red shift of the intense N3−→Pt LMCT band and the appearance of transitions with significant intensity in the visible region of the spectrum. The dissociative nature of the low-lying unoccupied orbitals remains unaffected. These theoretical results may suggest new experimental routes for the improvement of the photochemical activity of PtIVdiazido complexes. [ABSTRACT FROM AUTHOR]

Azulene is reported to react with Mn2(CO)10to give trans-C10H8Mn2(CO)6, which has been shown by X-ray crystallography to have a bis(pentahapto) structure with no metal-metal bond. This structure is found by density functional theory to be the lowest energy C10H8Mn2(CO)6structure. However, a corresponding bis(pentahapto) cis-C10H8Mn2(CO)6structure, also without an MnMn bond, lies within ∼1 kcal mol−1of this global minimum. The lowest energy C10H8Mn2(CO)5structure is singlet cis-η5,η5-C10H8Mn2(CO)5with an Mn→Mn dative bond from the Mn(CO)3group to the Mn(CO)2group. However, a singlet cis-η6,η4-C10H8Mn2(CO)5structure with a normal Mn–Mn single bond lies within ∼6 kcal mol−1of this global minimum. The lowest energy structures of the more highly unsaturated C10H8Mn2(CO)n(n= 4, 3, 2) systems all have cisgeometries and manganese-manganese bonds of various orders. The corresponding global minima are triplet cis-η5,η3-C10H8Mn2(CO)3(η2-μ-CO) for the tetracarbonyl with a four-electron donor bridging carbonyl group, singlet cis-η5,η5-C10H8Mn2(CO)3for the tricarbonyl, and triplet cis-η6,η4-C10H8Mn2(CO)(η2-μ-CO) for the dicarbonyl. [ABSTRACT FROM AUTHOR]

Recent work has resulted in the discovery of the fluorocarbyne complex (η5-C5H5)Mo(CO)2(CF), in which the CF ligand behaves as a formal three-electron donor like the isoelectronic well-known NO ligand. In this connection the related fluorocarbyne cobalt carbonyls Co(CF)(CO)n(n= 3, 2, 1) and Co2(CF)2(CO)n(n= 6, 5, 4, 3, 2) have been studied by density functional theory. The lowest energy structures for the mononuclear Co(CF)(CO)nderivatives parallel those of the isoelectronic Co(NO)(CO)nand Ni(CO)n+1derivatives. The mononuclear fluorocarbyne complex Co(CF)(CO)3is predicted to be thermodynamically unstable with respect to dimerization to the difluoroacetylene complex (FCCF)Co2(CO)6by ∼46 kcal mol−1. The binuclear Co2(CF)2(CO)nstructures can broadly be divided into two classes: (1) Structures in which the two CF ligands are coupled to form a Co2C2tetrahedrane derivative containing an FCCF ligand derived from difluoroacetylene; (2) Structures maintaining separate CF ligands. With important exceptions, the structures of the difluoroacetylene complexes (FCCF)Co2(CO)n(n= 6, 5, 4) parallel for the most part the structures predicted for the corresponding unsubstituted acetylene complexes. The relative energies of the Co2(CF)2(CO)nstructures with separate CF ligands indicate that the CF ligand is a more favorable bridging ligand than the ubiquitous CO ligand. [ABSTRACT FROM AUTHOR]

Noncovalent complexes of a tumorigenic benzo[a]pyrene diol epoxide with the guanine−cytosine (GC) and adenine−thymine (AT) base pairs have been examined computationally. ()-BaP DE-2 forms covalent adducts with DNA via nucleophilic attack on the ()-BaP DE-2 epoxide. Computational results predict five thermodynamically accessible complexes of AT with ()-BaP DE-2 that are compatible with intact DNA. Among these, two are expected to lead to adenine adducts. In the lowest energy AT···()-BaP DE-2 complex, which has a gas-phase interaction energy of −20.9 kcal mol−1, the exocyclic NH2of adenine is positioned for backside epoxide attack and formation of a transadduct. The most energetically favorable complex leading to formation of a cisring-opened adduct lies only 0.6 kcal mol−1higher in energy. For GC···()-BaP DE-2, there are only two thermodynamically accessible complexes. The higher-lying complex, bound in the gas phase by 24.4 kcal mol−1relative to separated GC and ()-BaP DE-2, would lead to a transring-opened N2-guanine adduct. In the global minimum energy GC···()-BaP DE-2 complex, bound by 27.3 kcal mol−1, the exocyclic NH2group of cytosine is positioned for cisepoxide addition. However, adducts of ()-BaP DE-2 with cytosine are rarely observed experimentally. The paucity of cytosine adducts, despite the predicted thermodynamic stability of this GC···()-BaP DE-2 complex, is attributed to the electrostatic destabilization of the benzylic cation intermediate thought to precede cisaddition. [ABSTRACT FROM AUTHOR]

AIIIBVcompounds are important for the development of advanced ceramic semiconductor and nanoelectronic materials, solar cell elements, and light-emitting diodes. A series of these group 13−15 compounds of the general formula M4Y4H8(M = B, Al, Ga; Y = N, P, As) has been theoretically studied at the B3LYP/TZVP level of theory. The stability of different isomer structures is discussed to reveal the competitiveness of group 13−13, group 13−15, and group 15−15 bonding. Preferential bonding patterns are established, and trends in the stability with respect to M and Y are also discussed. New structural types, featuring perfectly planar M4and Y4rings, have been established. [ABSTRACT FROM AUTHOR]