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Silver and copper clusters capped by external chelating dithiolate ligands can be classified according to the cavities in their central coinage metal polyhedra. Silver clusters composed exclusively of fused tetrahedra are analogous to simple saturated organic compounds. The only interstitial atom that can be fit into an Ag4 tetrahedron is hydrogen. Silver polyhedra with larger trigonal prismatic or cubic cavities, including highly distorted cubic cavities, can accommodate halide and chalcogenide anions. The still larger 12-vertex icosahedral and cuboctahedral coinage metal cavities can accommodate oxoanions of the types SO32− and SO42− and their heavier congeners or alternatively interstitial coinage or platinum group metals leading to central M′@M12 units. Copper clusters with central cuboctahedra and silver clusters with central icosahedra possessing interstitial metal atoms approximate sphericality and provide examples of electron-rich metal superatoms with an average metal oxidation state of less than +1. Such copper cluster superatoms have two extra electrons corresponding to a filled 1S2 superatomic orbital. The silver cluster superatoms are electron richer with eight extra electrons corresponding to filled 1S2 + 1P6 superatomic orbitals. In these silver clusters seven or eight faces of the central Ag12 icosahedron are capped by additional silver atoms in order to provide these additional electrons. [ABSTRACT FROM AUTHOR]

The reaction of Mn(CO)5Br with sodium ethylenedithiolate was reported in 1968 to give a dark red binuclear H2C2S2Mn2(CO)6 complex possessing the unusual property of complexing reversibly with ammonia to give a yellow H2C2S2Mn2(CO)6·NH3 adduct. In order to provide some insight into the nature of this adduct, density functional studies were performed on the H2C2S2Mn2(CO)n (n = 4 to 8) systems as well as their relevant ammonia and trimethylphosphine adducts. These theoretical studies support the structure of H2C2S2Mn2(CO)6 originally suggested 50 years ago involving the binding of the ethylenedithiolate C=C double bond as well as the sulfur atoms to the Mn2 unit with a bonding Mn–Mn distance of ∼2.8 Å. Complexation of H2C2S2Mn2(CO)6 with NH3 or Me3P preserves the complexed C=C double bond of the ethylenedithiolate ligand but lengthens the Mn…Mn distance to a non-bonding ∼3.6 Å. Thus H2C2S2Mn2(CO)6 represents a novel type of Lewis acid where reversible complexation with Lewis bases involves the rupture of a metal–metal bond. Carbonyl dissociation energies in the H2C2S2Mn2(CO)n series account for the formation of the hexacarbonyl H2C2S2Mn2(CO)6 as the stable product from the Mn(CO)5Br/ethylenedithiolate reaction. [ABSTRACT FROM AUTHOR]

The structures and energetics of the tetracarbaboranes C4Bn−4Hn (n = 6 to 13) have been investigated by density functional theory and coupled cluster calculations. In general, the lowest energy structures of the tetracarbaboranes C4Bn−4Hn minimize the number of C–C polyhedral edges as well as the degrees of the carbon vertices. For the C4B2H6 and C4B3H7 systems the lowest energy structures are pyramidal structures having all four carbon atoms located on the base of the pyramid. The lowest energy structure for the 9-vertex C4B5H9 system is a capped square antiprism. The frameworks of the lowest energy C4B4H8 and C4B6H10 structures resemble those of the isoelectronic experimentally known B8H12 and B10H14 structures. However, an experimentally known S4 adamantane-like 10-vertex structure found in Me4C4B6Et6 based on a tetracapped octahedron lies only ∼7 kcal mol−1 in energy above the lowest energy structure. The lowest energy structures for the 11- to 13-vertex C4Bn−4Hn (n = 11, 12, 13) systems can be derived from an (n + 1)-vertex closo deltahedron by removing a high-degree vertex. At least three of the four carbon atoms are located on edges of the resulting pentagonal or hexagonal open face in the low-energy structures. However, the structures of the experimentally known R4C4B8H8 (R = Me, Et) obtained from the dimerization of R2C2B4H42− differ from these low-energy structures. The Me4C4B8H8 polyhedron has a C4 chain and two tetragonal faces whereas the Et4C4B8H8 polyhedron has a hexagonal face with two C2 units. These structures lie within 2 kcal mol−1 of each other thereby accounting for the fluxional properties of these systems observed by NMR spectroscopy. [ABSTRACT FROM AUTHOR]

Uhl and coworkers have synthesized and characterized structurally the 11-vertex tetracarbalanes (AlMe)7(CEt)4(μ-H)2 and (AlEt)7(CCH2Ph)4(C≡CPh)(μ–H). In order to understand the nature of the unusual C4Al7 polyhedra in such systems, the complete series of permethylated tetracarbalanes C4Aln−4Men (n = 6 to 14) as model compounds have been investigated using density functional theory. An overriding factor in determining the polyhedra for the lowest energy structures of a wide range of tetracarbalanes C4Aln−4Men (n = 6 to 14) is the availability of vertices of degrees 3 and 4 for all four carbon atoms. For the 11-vertex C4Al7Me11 system the experimentally observed C4Al7 deltahedron with carbon atoms at the four degree 4 vertices is found in the lowest energy structure but severely distorted from ideal C2h to Cs symmetry. This distortion is removed by adding two bridging hydrogens to the C4Al7Me11 structure in the same locations as in the experimental structures. The lowest energy structures of the tetracarbalanes C4Aln−4Men (n = 12, 13, 14) with more than 11 vertices are deltahedra having the carbon atoms at degree 4 vertices similar to the lowest energy C4Al7Me11 structures. The lowest energy structures for the smaller tetracarbalanes C4Aln−4Men (n = 6, 7, 8) are nido structures with pentagonal or hexagonal open faces related to nido borane structures. The intermediate 9- and 10-vertex tetracarbalanes C4Aln−4Men (n = 9, 10) have relatively complicated energy surfaces. [ABSTRACT FROM AUTHOR]

The structures and energetics of the complete series of hydrogen-rich dimetallaboranes Cp2M2B6H10 and Cp*2M2B6H10 (Cp = η5-C5H5; Cp* = η5-Me5C5; M = Pd, Pt; Rh, Ir; Ru, Os; Re; Mo, W; Ta), including the experimentally known Cp*2Rh2B6H10 and Cp*2W2B6H10 (Cp* = η5-Me5C5), have been investigated by density functional theory. The lowest energy structures of the hyperelectronic Cp2M2B6H10 (M = Pd, Pt; Rh, Ir) systems have central M2B6 frameworks with a hexagonal open face similar to the B8 networks in arachno-B8H14 and nido-B8H12. The two lowest energy structures for Cp2Rh2B6H10 and Cp*2Rh2B6H10, lying within 1 kcal mol−1 of energy, differ only in the locations of the bridging hydrogen atoms around the hexagonal hole consistent with the experimentally observed fluxionality of the hydrogen atoms in Cp*2Rh2B6H10. Most of the lowest energy Cp2M2B6H10 (M = Ru, Os) structures also have a central M2B6 framework similar to B8H12, typically with such additional features as an additional metal–metal bond or a formal metal–metal double bond. A common motif for the low-energy structures of the hypoelectronic Cp2M2B6H10 (M = Re; Mo, W; Ta) systems, including the experimentally known Cp*2W2B6H10, is a central M2B4 octahedron with its two M2B faces capped by the remaining boron atoms and with four M–B edges bridged by hydrogen atoms. Such structures can also be considered as oblatonido structures derived from the experimentally known 9-vertex oblatocloso Cp*2Re2B7H7 structure by removal of the unique degree 4 vertex atom. [ABSTRACT FROM AUTHOR]

The structures of five-vertex dimetallaboranes Cp2M2B3H7 (Cp = η5-C5H5) of the second and third row transition metals, including the experimentally known Cp*2Rh2B3H7 (Cp* = η5-Me5C5), have been investigated by density functional theory. The predicted low-energy structures for Cp2M2B3H7 (M = Rh, Ir) are tetragonal pyramids similar to Cp*2Rh2B3H7 and pentaborane-9 B5H9 and consistent with their 14 Wadean skeletal electrons. Two Cp*2Rh2B3H7 structures with the same central Rh2B3 tetragonal prism are found with energies within ∼1 kcal mol−1 of each other, consistent with the experimental observation of two isomers in solution. The electron-richer Cp2M2B3H7 (M = Pd, Pt) systems having 16 Wadean skeletal electrons are predicted to exhibit more open structures analogous to the known structure for the valence isoelectronic pentaborane-11 B5H11. Trigonal bipyramids with the metal atoms at equatorial vertices are typically found to be low-energy structures for the hypoelectronic Cp2M2B3H7 systems (M = Ru, Os, Re, Mo, W, Ta). In addition, the low-energy Cp2Re2B3H7 structures of the rhenium derivatives Cp2Re2B3H7 provide examples of structures based on a central Re2B2 tetrahedron with the Re–Re edge bridged by the third boron atom. Such structures can be derived from a trigonal bipyramid by the rupture of one of the axial–equatorial edges. [ABSTRACT FROM AUTHOR]

The neutral ferratricarbaboranes (η5-RC3B8H10)Fe(η5-C5H5) (R = aryl), analogues of ferrocene, have recently (2013) been synthesized by Štíbr and co-workers and structurally characterized by X-ray crystallography. We have now used density functional theory to study the structures of the complete series of related ferratricarbaboranes CpFeC3Bn-4Hn-1 (n = 8 to 12). The lowest energy structures are found to have the maximum number of carbon atoms at degree 4 rather than at degree 5 vertices and avoid adjacent carbon atoms, i.e., C-C edges. This can lead to structures deviating from the most spherical closo deltahedra. For the 8-vertex CpFeC3B4H7 system, hexagonal bipyramidal structures are found to be of comparable energy to the closo bisdisphenoidal structures. For the 9-vertex CpFeC3B5H8 system the unique closo tricapped trigonal prismatic structure having carbon atoms at the three non-adjacent degree 4 vertices lies ∼16 kcal mol-1 below the next lowest energy structure. The 10-vertex CpFeC3B6H9 system has the most complicated potential energy surface of the CpFeC3Bn-4Hn-1 structures with nine structures within 13 kcal mol-1 of the global minimum. Six of these nine structures are based on the closo bicapped square antiprism, which has only two degree 4 vertices for carbon atoms. The remaining three lowenergy CpFeC3B6H9 structures are derived from the isocloso 10-vertex deltahedron with the iron atom at the unique degree 6 vertex and all three carbon atoms at degree 4 vertices. The low-energy 11-vertex CpFeC3B7H10 structures are based on the 11-vertex closo/isocloso deltahedron with the unique structure having the iron atom at the degree 6 vertex, carbon atoms at the two degree 4 vertices, and no C-C edge being the lowest energy structure. The lowest energy 12-vertex CpFeC3B8H11 structures are all based on the regular icosahedron with the three lowest energy structures having no C-C edges. The two lowest energy CpFeC3B8H11 structures correspond to those recently found experimentally in the (η5-RC3B8H10)- Fe(η5-C5H5) (R = aryl) systems. [ABSTRACT FROM AUTHOR]

Theoretical studies on Co2(CO)6(PX)2derivatives (X = H, Cl, OH, OMe, NH2, NMe2) predict the lowest energy structures to be butterfly structures containing five two-electron two-center bonds in the central Co2P2unit. Among these butterfly structures the energy increases as the unique bond forming the “body” of the butterfly changes from Co–Co to Co–P and then P–P. Higher energy rhombus structures are also found for Co2(CO)6(PX)2with only Co–P bonds in the Co2P2framework without any Co–Co or P–P bonds. In addition, for Co2(CO)6(POR)2(R = H, Me) still higher energy “diphosphine” structures are also found containing only three rather than four Co–P bonds, one P–P bond, and no CoCo bond. For the isoelectronic Co2(CO)6S2a rhombus structure is competitive in energy with the butterfly structures with five structures lying within ∼4 kcal/mol thereby predicting a fluxional system. A tetrahedrane structure was not found for Co2(CO)6S2in contrast to the tetrahedrane structure known experimentally for the related Fe2(CO)6S2with one less electron per metal atom. [ABSTRACT FROM AUTHOR]

The structures of the mononuclear derivatives HMn(CO)n (n = 4 and 3) are shown by density functional theory (B3LYP and PB86) to derive from octahedral HMn(CO)5 by losses of various combinations of carbonyl groups with relatively little change in the C-Mn-C angles involving the remaining carbonyl groups. The binuclear H2Mn2(CO)n structures are predicted to have bridging hydrogen atoms in preference to bridging carbonyl groups. Thus, two structures are found for the binuclear H2Mn2(CO)9, isoelectronic with Fe2(CO)9, in which all nine of the carbonyl groups are terminal carbonyl groups. The lowest lying H2Mn2(CO)9 structure is the dihydrogen complex (OC)5Mn-Mn(CO)4(η2-H2), in which one of the equatorial CO groups of Mn2(CO)10 is replaced by a dihydrogen ligand. A slightly higher energy H2Mn2(CO)9 structure by ∼6 kcal mol1- has an Mn-Mn bond bridged by a single hydrogen and all terminal carbonyl groups as well as a single terminal hydrogen. The H2Mn2(CO)8 molecule is predicted to have a structure with a central Mn(μ-H)2Mn core related to diborane. In this structure the manganese-manganese bond of length 2.703Å (BP86) can be considered the diprotonated formal double bond required to give both manganese atoms the favoured 18-electron configuration. The more highly unsaturated H2Mn2(CO)n (n = 7, 6) derivatives have similar structures derived from the H2Mn2(CO)8 structure by loss of one or two carbonyl groups. In many cases the Mn=Mn distance in the central Mn(μ-H)2Mn unit shortens to ∼2.4Å suggesting a diprotonated triple bond. [ABSTRACT FROM AUTHOR]

Trinuclear cyclopentadienylniobium carbonyls are of interest since Cp3Nb3(CO)7 (Cp = η5-C5H5) is a stable molecule having a unique face-bridging carbonyl group formally donating six electrons to the Nb3 triangle through one Nb-C σ-bond and two orthogonal π-bonds. In this connection, the molecules Cp3Nb3(CO)n (n = 9, 8, 7, 6) have been examined by density functional theory. The saturated derivative Cp3Nb3(CO)9 is predicted to have a structure with all terminal carbonyl groups and a singly bonded Nb3 triangle with 3.361Å edges. The singly bonded Nb3 triangle is retained in the lowest energy structure for Cp3Nb3(CO)8, which has a four-electron donor edge-bridging carbonyl group in addition to seven terminal carbonyl groups. An alternative structure for Cp3Nb3(CO)8 at ∼8 kcal mol-1 above this global minimum has an unusual four-electron donor carbonyl group bridging all three niobium atoms. The two lowest energy structures found for Cp3Nb3(CO)7 are a pair of stereoisomers within ∼1 kcal mol-1 of energy, having a six-electron donor carbonyl group bridging all three niobium atoms, in addition to six terminal carbonyl groups. The structure and n(CO) frequencies of one of these stereoisomers, including the unusually low n(CO) frequency of ∼1330 cm-1 for the six electron donor carbonyl group, are in close agreement with experiment. In contrast to Cp3Nb3(CO)8 and Cp3Nb3(CO)7, the lowest energy structure for the even more unsaturated Cp3Nb3(CO)6 has only two-electron donor carbonyl groups, three of which are edge-bridging and three of which are terminal. However, in this Cp3Nb3(CO)6 structure, two of the Nb=Nb distances in the Nb3 triangle are shortened to ∼2.8Å , suggesting a formal bond order of at least two. [ABSTRACT FROM AUTHOR]

Trinuclear cyclopentadienylniobium carbonyls are of interest since Cp3Nb3(CO)7(Cp = η5-C5H5) is a stable molecule having a unique face-bridging carbonyl group formally donating six electrons to the Nb3triangle through one Nb–C σ-bond and two orthogonal π-bonds. In this connection, the molecules Cp3Nb3(CO)n(n= 9, 8, 7, 6) have been examined by density functional theory. The saturated derivative Cp3Nb3(CO)9is predicted to have a structure with all terminal carbonyl groups and a singly bonded Nb3triangle with 3.361 edges. The singly bonded Nb3triangle is retained in the lowest energy structure for Cp3Nb3(CO)8, which has a four-electron donor edge-bridging carbonyl group in addition to seven terminal carbonyl groups. An alternative structure for Cp3Nb3(CO)8at ∼8 kcal mol−1above this global minimum has an unusual four-electron donor carbonyl group bridging all three niobium atoms. The two lowest energy structures found for Cp3Nb3(CO)7are a pair of stereoisomers within ∼1 kcal mol−1of energy, having a six-electron donor carbonyl group bridging all three niobium atoms, in addition to six terminal carbonyl groups. The structure and ν(CO) frequencies of one of these stereoisomers, including the unusually low ν(CO) frequency of ∼1330 cm−1for the six electron donor carbonyl group, are in close agreement with experiment. In contrast to Cp3Nb3(CO)8and Cp3Nb3(CO)7, the lowest energy structure for the even more unsaturated Cp3Nb3(CO)6has only two-electron donor carbonyl groups, three of which are edge-bridging and three of which are terminal. However, in this Cp3Nb3(CO)6structure, two of the NbNb distances in the Nb3triangle are shortened to ∼2.8 , suggesting a formal bond order of at least two. [ABSTRACT FROM AUTHOR]

The binuclear homoleptic rhodium carbonyls Rh2(CO)n (n = 8, 7, 6, 5) have been examined theoretically. Three energetically low-lying equilibrium structures of Rh2(CO)8 were found, i.e., one doubly bridged C2v singlet structure and two unbridged singlet structures with D3d and D2d symmetry. The doubly bridged structure is the global minimum predicted to lie 3.4 kcal/mol below the D2d structure and 6.4 kcal/mol below the D3d structure. For Rh2(CO)7 the global minimum is either a singlet C2v unbridged structure or a singlet doubly bridged Cs structure within 1.8 kcal/mol depending upon the theoretical method. For Rh2(CO)6, the global minimum is either a singlet doubly bridged D2 structure or a singlet unbridged D2d structure depending upon the method. Triplet structures for Rh2(CO)7 and Rh2(CO)6 are predicted to be of high energies relative to the low energy singlet structures. For Rh2(CO)5 the C2v singlet singly bridged structure lies below the C2 or C2v triplet structures. [ABSTRACT FROM AUTHOR]

The binuclear homoleptic rhodium carbonyls Rh2(CO)n(n= 8, 7, 6, 5) have been examined theoretically. Three energetically low-lying equilibrium structures of Rh2(CO)8were found, i.e., one doubly bridged C2vsinglet structure and two unbridged singlet structures with D3dand D2dsymmetry. The doubly bridged structure is the global minimum predicted to lie 3.4 kcal/mol below the D2dstructure and 6.4 kcal/mol below the D3dstructure. For Rh2(CO)7the global minimum is either a singlet C2vunbridged structure or a singlet doubly bridged Csstructure within 1.8 kcal/mol depending upon the theoretical method. For Rh2(CO)6, the global minimum is either a singlet doubly bridged D2structure or a singlet unbridged D2dstructure depending upon the method. Triplet structures for Rh2(CO)7and Rh2(CO)6are predicted to be of high energies relative to the low energy singlet structures. For Rh2(CO)5the C2vsinglet singly bridged structure lies below the C2or C2vtriplet structures. [ABSTRACT FROM AUTHOR]

Comparison of theoretical and experimental structural parameters as well as v(CO) frequencies for Os3(CO)12 suggests that the density functional theory (DFT) method MPW1PW91 with a suitable ECP basis set including relativistic effects is a reliable method for predicting structures and vibrational frequencies of third row transition metal carbonyl derivatives. Using this method the structures of the unsaturated trinuclear osmium carbonyl derivatives Os3(CO)n (n = 11, 10, 9) have been investigated for comparison with their iron carbonyl analogues. For Os3(CO)11 the global minimum has µ-CO groups bridging each edge of the Os3 triangle in contrast to its iron analogue predicted to have two µ3-CO groups bridging all three iron atoms. An alternative Os3(CO)11 structure having only terminal CO groups, similar to that observed experimentally by Bentsen and Wrighton (J. G. Bentsen and M. S. Wrighton, J. Am. Chem. Soc., 1987, 109, 4518) in the photolysis of Os3(CO)12 in low temperature hydrocarbon matrices, is predicted to lie ~7 kcal mol−1 above this global minimum. The global minimum for Os3(CO)10 has one face-bridging µ3-CO group and one edge-bridging µ-CO group. For Os3(CO)9 the global minimum has an Os3 scalene triangle with different metal-metal distances suggesting one single, one double, and one triple metal-metal bond similar to its iron analogue. [ABSTRACT FROM AUTHOR]