Trends in the Structures and Energetics of the Group 14 Metallocenes (C5H5)2M (M = Si−Pb): A Density Functional Theory Study

The molecular structure of [Sn(P2C2But2)] using gas-phase electron diffraction and DFT calculations

The molecular structure of 2,4-di-tert-butyl-eta4-1,3-diphosphacyclobutadiene tin has been determined in the gas phase by electron diffraction using both the DYNAMITE and SARACEN methods. The suitability of many different theoretical methods for the calculation of structures of half-sandwich main-group metal complexes has been investigated, and, by comparison of the results with the experimental structures, suggestions have been made as to the most suitable methods for this class of compound.

Group 14 triple-decker cations

The triple-decker cations trans-[(Cp*Sn)(2)(mu-eta(5):eta(5)-Cp*)](+) and trans-[(Cp*Pb)(2)(mu-eta(5):eta(5)-Cp*)](+) have been prepared and structurally characterized as their [B(C(6)F(5))(4)](-) salts from the reactions of [Cp*M][B(C(6)F(5))(4)](M = Sn, Pb) with the appropriate decamethylmetallocene. Both triple-decker cations adopt a cisoid arrangement of terminal Cp* groups, whereas the two known triple-decker main-group anions possess a transoid arrangement of terminal Cp groups. The reason for this conformational difference has been probed on the basis of DFT calculations.

Do penta- and decaphospha analogues of lithocene anion and beryllocene exist? Analysis of stability, structure, and bonding by hybrid density functional study

Stability in penta- and decaphospha analogues of lithocene anion and beryllocene is investigated by complete structural optimization at the B3LYP/6-31G level. Natural bond orbital analysis is carried out to examine the bonding between the metal and the ligands. The heterolytic dissociation energies of 667 and 608 kcal/mol predicted by B3LYP/6-311+G//B3LYP/6-31G calculations for CpBeP(5) and (P(5))(2)Be are comparable with the observed value of 635 +/- 15 kcal/mol in ferrocene. The high stability in CpBeP(5) and (P(5))(2)Be shows that these species are isolable under appropriate conditions. Lithocene anion and its phospha analogues possess lower stability toward dissociation into ionic fragments. A novel observation of the present study is that CpBeP(5) and (P(5))(2)Be have lowest energies when the two planar ligands are arranged perpendicular to each other such that one of the ligands, cyclo-P(5), is eta(1)-coordinated while the second ligand is eta(5)-coordinated to Be. The resulting structure having C(s)() point group (denoted as C(s)()(p)) is predicted to be 22 and 28 kcal/mol lower than the staggered sandwich geometry in CpBeP(5) and (P(5))(2)Be, respectively, at the B3LYP/6-311+G//B3LYP/6-31G level. In the analogous lithocene anions [CpLiP(5)](-) and [(P(5))(2)Li](-) also the C(s)()(p) structures are found to be the lowest energy structures, though their relative stabilities are small. We also characterized the geometry with both ligands eta(1)-coordinated to the metal in a linear arrangement having the D(2)(h)() point group in the decaphospha analogues [(P(5))(2)Li](-) and (P(5))(2)Be. This structure is found to be higher in energy than the C(s)()(p) structure. The D(2)(h)() structure could not be located as a potential minimum in the biscyclopentadienyl complexes and their pentaphospha analogues. Both the C(s)()(p) and D(2)(h)() structures are characterized for the first time in metallocenes. The D(2)(h)() structure seems to be a unique feature in the decaphospha metallocenes under consideration. Covalent bond formation between beryllium and phosphorus atom P(1) of eta(1)-(cyclo-P(5)) is more pronounced (bond orders 0.43-0.49) than that between Be and C(1) of eta(1)-Cp (bond orders 0.24-0.27). Though both eta(1)-coordinated cyclo-P(5) and Cp exhibit C(2)(v)() point groups, bond alternation is less pronounced in the former. The Wiberg P-P bond orders in the eta(1)-(cyclo-P(5)) of CpBeP(5) and (P(5))(2)Be having C(s)()(p) structures are in the range 1.29-1.47. These ring bond orders indicate that the P(5) ring retains aromaticity to a large extent in the eta(1)-mode of bonding with Be. Second-order perturbational energy analysis of the Fock matrix in the natural bond orbital basis reveals that there is a significant stabilizing interaction of approximately 123 kcal/mol between the lone pair orbital of P(1) and the 2s orbital of Be in the C(s)()(p) structures.

Reactions between M+ (M = Si, Ge, Sn and Pb) and benzene in the gas phase

Using a laser ablation/inert buffer gas ion source coupled with a reflectron time-of-flight mass spectrometer, the gas-phase reactions between the IVA group element ions M(+) (M = Si, Ge, Sn and Pb) and benzene seeded in argon gas were studied. In addition to the association reaction pathway (forming [M(C(6)H(6))(x)](+), x = 1, 2, etc.), benzene was dissociated to form complex ions [M(C(5)H(5))](+), [M(C(7)H(5))](+) and [M(C(9)H(x))](+) (x = 5, 7 and 9), etc. DFT theoretical calculations indicated that, in the association products [M(C(6)H(6))](+), the M atom is close to one carbon atom of benzene, while in most of the dissociation complexes, pentagonal structures (M/cyclopentadienyl derivatives) were formed, with the M atom situated near the fivefold axis of the five-membered ring. The bond patterns in these complexes are discussed.

Interpreting molecular crystal disorder in plumbocene, Pb(C5H5)2: insight from theory

Plane-wave density functional theory has been applied in a novel way to help interpret the molecular crystal structure disorder observed in the orthorhombic zigzag phase of plumbocene, Pb(C5H5)2. A crystal lattice comprising uniformly staggered C5H5 rings was found to be lower in energy by 2.8 kJ mol-1 per unit cell, compared to a uniformly eclipsed packing arrangement. This energy difference has been attributed to the difference in the strength of intermolecular interactions between the Pb(C5H5)2 chains for the two different lattices. The calculations performed allowed the determination of the crystallographic occupancy factors by a quantum mechanical technique for the first time.

Syntheses and solid state structures of tris(pyrazolyl)methane complexes of sodium, potassium, calcium, and strontium: comparison of structures with analogous complexes of lead(II)

The reaction of NaI with 2 equiv of HC(pz)(3) or HC(3,5-Me(2)pz)(3) (pz = pyrazolyl ring) leads to the formation of [[HC(pz)(3)](2)Na](I) (1) and [[HC(3,5-Me(2)pz)(3)](2)Na](I) (2), respectively. Both compounds have trigonally distorted octahedral arrangements about the sodium. A similar reaction of KPF(6) with HC(3,5-Me(2)pz)(3) results in the formation of [[HC(3,5-Me(2)pz)(3)](2)K](PF(6)) (3), a complex also shown crystallographically to have a trigonally distorted octahedral arrangement about the potassium, which is an unusually low coordination number for this large metal ion. The complex [[HC(pz)(3)](2)Sr](BF(4))(2) (4) forms in the reaction of Sr(acac)(2) (acac = acetylacetonate) with HBF(4).Et(2)O followed by 2 equiv of HC(pz)(3). The structure is highly distorted, showing kappa(3) bonding of both tris(pyrazolyl)methane ligands and, in addition, interactions with the metal from three fluorine atoms from the BF(4)(-) counterions. The symmetrical structure of 1 and the nine-coordinate structure of 4 are both very different from the distorted, six-coordinate structure [[HC(pz)(3)](2)Pb](BF(4))(2), indicating that for this compound the lone pair on lead(II) is influencing the structure. The reaction of M(acac)(2) (M = Sr, Ca) with H[B[3,5-(CF(3))(2)C(6)H(3)](4)] followed by 2 equiv of HC(pz)(3) produces [[HC(pz)(3)](2)(Hacac)Sr][B[3,5-(CF(3))(2)C(6)H(3)](4)](2) (5) (when the reaction is done in CH(2)Cl(2)), [[HC(pz)(3)](2)(Me(2)CO)(2)Sr][B[3,5-(CF(3))(2)C(6)H(3)](4)](2) (6) (when the reaction is done in acetone), and [[HC(pz)(3)](2)(Hacac)Ca][B[3,5-(CF(3))(2)C(6)H(3)](4)](2)(7), respectively. The structures of all three complexes show a distorted eight-coordinate arrangement of the ligands about the metal. Crystal data: 1 is orthorhombic, Pnma, a = 16.931(1), b = 22.368(3), c = 7.937(2) A, alpha = 90, beta = 90, gamma = 90 degrees, Z = 4; 2 is trigonal, R3, a = 10.7483(8), b = 10.7483(8), c = 35.395(4) A, alpha = 90, beta = 90, gamma = 120 degrees, Z = 3; 3 is monoclinic, P2(1)/c, a = 9.144(4), b = 13.377(6), c = 15.988(7) A, alpha = 90, beta = 92.291(10), gamma = 90 degrees, Z = 2; 4 is hexagonal, P6(5), a = 9.42530(10), b = 9.42530(10), c = 55.3713(5) A, alpha = 90, beta = 90, gamma = 120 degrees, Z = 6; 5 is monoclinic, P2/n, a = 14.1601(3), b = 13.1756(3), c = 27.1826(6) A, alpha = 90, beta = 90.1744(7), gamma = 90 degrees, Z = 2; 6 is monoclinic, P2/n, a = 14.2709(7), b = 13.2646(7), c = 27.4189(13) A, alpha = 90, beta = 90.3850(10), gamma = 90 degrees, Z = 2; 7 is monoclinic, P2/n, a = 14.2388(2), b = 13.1919(2), c = 26.7879(3) A, alpha = 90, beta = 90.0650(8), gamma = 90 degrees, Z = 2.