Nonempirical wave functions for very large molecules. I. The PRDDO/M method

We describe enhancements to the method of partial retention of diatomic differential overlap (PRDDO ). The new method, denoted PRDDO/M , employs a basis set of not quite orthogonal atomic orbitals (NQOAOS ) and utilizes sparse matrix techniques to greatly increase the computational efficiency for large molecules. Other modifications, including a complete reparametrization of the method against ab initio STO -3G calculations and implementation of integral screening/damping algorithms, are described. The method is an order of magnitude or more faster than are STO 3G single-point calculations using modern ab initio codes, with little loss in accuracy. © 1996 John Wiley & Sons, Inc.     

A unique coplanar multi-center bonding network in doubly acetylide-bridged binuclear zirconocene complexes: A density functional theory study

A unique π-conjugative interaction pattern was experimentally revealed in the doubly acetylide-bridged binuclear group 4 metallocene complexes, which was involved in C-C coupling/cleavage reactions of acetylides and σ-alkynyl migrations. To elucidate how this multi-center bonding network affects the structural and reaction properties of these complexes, density functional theory (DFT) calculations and molecular orbital (MO) analysis were carried out on the electronic structure and σ-alkynyl migration mechanisms of the doubly acetylide-bridged binuclear Zr complexes, (L₂Zr)₂(μ-CCH)₂ (L = Cp, Cl). The B3LYP calculations suggested that the doubly [σ,π] acetylide-bridged complex C_2h-(L₂Zr)₂(μ-CCH)₂ was produced by the reaction of L₂Zr(CCH)₂ with L₂Zr through a C_2v-(L₂Zr)₂(μ-CCH)₂ intermediate followed by an isomerization process. In particular, the isomerization of C_2h- or C_2v-(L₂Zr)₂(μ-CCH)₂ is almost thermoneutral through a low barrier of 15.3-17.0 kcal/mol. The MO Walsh diagram revealed that the two isomers have a very similar six-center-six-electron bonding network. The coplanar π-conjunctive interaction by the electron donating and back-donating interactions between the metal centers and acetylide ligands significantly stabilizes the doubly acetylide-bridged binuclear group 4 metallocene complexes and the isomerization transition state.     

4,4-Difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) dyes modified for extended conjugation and restricted bond rotations

Five new, constrained, aryl-substituted 4,4-difluoro-4-bora-3a, 4a-diaza-s-indacene (BODIPY) dyes (3f,g and 4h-j) were prepared and investigated to see if they have more favorable fluorescence characteristics than the unconstrained systems 2 that were prepared in previous studies. Dye types 3 and 4 have relatively rigid conformations caused by the heteroatom (3f and 3g) or ethylene bridge (4h-j) linkers that preclude free rotation of the substituted-benzene molecular fragments. In the event, the new dye types 3 and 4 have longer lambda(max abs) (620-660 nm) and lambda(max)(fluor) (630-680 nm) values than compounds 2. They also exhibit higher extinction coefficients (>100 000 M(-1) cm(-1), except for 3g). Their fluorescent quantum yields are high (up to 0.72 for 4j), with the exception of compound 3g, which has a quantum yield of only 0.05. The redox properties of dyes 3 and 4 have also been examined.     

Unique reactivity of a tetradentate N(2)S(2) complex of nickel: intermediates in the production of sulfur oxygenates

Complex 1 [(N,N'-dimethyl-N,N'-bis(2-sulfanylethyl)ethylenediamine)nickel(II)], previously shown to react with H(2)O(2) to produce the fully oxygenated disulfonate 5 [diaqua(N,N'-dimethyl-N,N'-bis(2-sulfonatoethyl)ethylenediamine)nickel(II)], has been explored in detail to explain the observed reactivity of this compound and to discern intermediates in the oxygenation reaction. Reaction of 1 with 1 equiv of methyl iodide results in the monomethylated square-planar nickel complex 2 [[(N,N'-dimethyl-N-(2-sulfanylethyl)-N'-(2-methylthioethyl)(ethylenediamine)nickel(II)] iodide], while a slight excess of methyl iodide results in the dimethylated complex 3 [diiodo(N,N'-dimethyl-N,N'-bis(2-methylthioethyl)ethylenediamine)nickel(II)], an X-ray structure of which has shown that the nickel ion is in an octahedral N(2)S(2)I(2) environment. Crystal data of 3: monoclinic, a = 8.865(3) A, b = 14.419(4) A, c = 14.389(6) A, beta = 100.19(3) degrees, V = 1810.2(12) A(3), space group P2(1)/n, Z = 4. The equatorial positions are occupied by the two cis-amine N-atoms and the coordinated iodides, while the axial positions are occupied by the thioether sulfur atoms. In organic solvents, the dithiolate complex 1 reacts with molecular oxygen or H(2)O(2) to produce the mixed sulfinato/thiolato complex 4 [(N,N'-dimethyl-N-(2-sulfanylethyl)-N'-(2-sulfinatoethyl)(ethylenediamine)nickel(II)], and the fully oxidized product 5. X-ray analysis of complex 4 reveals a square-planar geometry in which the nickel ion is coordinated by two cis-amine nitrogens, one thiolate sulfur donor, and one sulfinato sulfur donor. Crystal data of 4: orthorhombic, a = 11.659(2) A, b = 13.119(3) A, c = 16.869(3) A, V = 2580.2(9) A(3), space group Pbca, Z = 8. This complex is the only intermediate in the oxygenation reaction that could be isolated, and it is shown to be further reactive toward O(2) to yield the fully oxidized product 5. For a better understanding of the reactivity observed for 4, DFT calculations have been undertaken, which show a possible reaction path toward the fully oxidized product 5.     

Nonempirical wave functions for very large molecules. II. The PRDDO/M/FCP method

A variation of the frozen-core potential (FCP) method is developed and implemented within the modified version of the method of partial retention of diatomic differential overlap (PRDDO/M). The explicit treatment of core electrons is replaced with a potential based on the actual core-valence integrals rather than upon an arbitrary model potential. The core-valence orthogonality requirement is replaced by an energy shift operator. PRDDO/M/FCP calculations exhibit good agreement with ab initio calculations with the same basis set, while reducing the computational cost significantly. © 1997 John Wiley & Sons, Inc.     

The origin of endocyclic bond length variations in disubstituted cyclotriphosphazenes

Intraannular ring alternation in heterogeneously substituted cyclotriphosphazenes is investigated using both ab initio and density functional methods. Comparisons of the calculated geometries for N3P3X6 (X = H, F, Cl, Me, Ph) and N3P3X4Y2 (X = F, Cl; Y = Me, Ph, X, Cl) with experimental X-ray data establish the utility of the 6-31G* basis for use with both Hartree-Fock and the B3LYP and B3PW91 functionals. Analysis of orbitals and charges shows that the bonding is best described using a polarized bond model rather than the previous explanation of asymmetric nitrogen-lone-pair donation into the phosphorus-nitrogen bond.     

New volatile strontium and barium imidazolate complexes for the deposition of group 2 metal oxides

We report the synthesis, characterization, and experimental density function theory-derived properties of new volatile strontium and barium imidazolate complexes, which under atomic layer deposition conditions using ozone as a reagent can deposit crystalline strontium oxide at 375 °C.