Malcolm H. Chisholm (1945-2015).

Malcolm H. Chisholm, Distinguished Professor of Mathematical and Physical Sciences at The Ohio State University, passed away on November 20, 2015. He is best known for his pioneering work on the chemistry of metal-metal multiple bonds, the molecular and electronic structure and bonding of transition-metal compounds, and the exploration of excited states of complexes with metal-metal quadruple bonds.

Detection and Electronic Structure of Naked Actinide Complexes: Rhombic-Ring (AnN)2 Molecules Stabilized by Delocalized π-Bonding.

The major products of the reaction of laser ablated and excited U atoms and N2 are the linear N≡U≡N dinitride molecule, isoelectronic with the uranyl dication, and the diatomic nitride U≡N. These molecules form novel cyclic dimers, (UN)2 and (NUN)2, with complex electronic structures, in matrix isolation experiments, which increase on UV photolysis. In addition, (NUN)2 increases at the expense of (UN)2 upon warming the codeposited matrix samples into the 20-40 K range as attested by additional nitrogen and argon matrix infrared spectra recorded after cooling the samples back to 4 or 7 K.

Metathesis of nitrogen atoms within triple bonds involving carbon, tungsten, and molybdenum.

(ButO)3Mo triple bond N and W2(OBut)6(M triple bond M) react in hydrocarbons to form Mo2(OBut)6(M triple bond M) and (ButO)3W triple bond N via the reactive intermediate MoW(OBut)6(M triple bond M). (ButO)3W triple bond N and CH3C triple bond N15 react in tetrahydrofuran (THF) at room temperature to give an equilibrium mixture involving (ButO)3W triple bond N15 and CH3C triple bond N. The (ButO)3W triple bond N compound is similarly shown to act as a catalyst for N15-atom scrambling between MeC13 triple bond N15 and PhC triple bond N to give a mixture of MeC13 triple bond N and PhC triple bond N15.

Infrared spectrum and bonding in uranium methylidene dihydride, CH2=UH2.

Uranium atoms activate methane upon ultraviolet excitation to form the methyl uranium hydride CH3-UH, which undergoes alpha-H transfer to produce uranium methylidene dihydride, CH2=UH2. This rearrangement most likely occurs on an excited-quintet potential-energy surface and is followed by relaxation in the argon matrix. These simple U+CH4 reaction products are identified through isotopic substitution (13CH4, CD4, CH2D2) and density functional theory frequency and structure calculations for the strong U-H stretching modes.

Structure and bonding in SnWO4, PbWO4, and BiVO4: lone pairs vs inert pairs.

Three ternary oxides, SnWO4, PbWO4, and BiVO4, containing p-block cations with ns2np0 electron configurations, so-called lone pair cations, have been studied theoretically using density functional theory and UV-visible diffuse reflectance spectroscopy. The computations reveal significant differences in the underlying electronic structures that are responsible for the varied crystal chemistry of the lone pair cations. The filled 5s orbitals of the Sn2+ ion interact strongly with the 2p orbitals of oxygen, which leads to a significant destabilization of symmetric structures (scheelite and zircon) favored by electrostatic forces.

Theoretical investigation of uranyl dihydroxide: oxo ligand exchange, water catalysis, and vibrational spectra.

Density functional theory is employed to investigate uranyl dihydroxide, UO2(OH)2, isomerization reaction energy barriers, including those occurring via proton shuttles. The ground-state structure of a uranyl dihydroxide complex containing a uranyl moiety with a near 90 degrees O=U=O bond angle is reported for the first time. Furthermore, we predict the vibrational spectra of these compounds.

Speciation of the curium(III) ion in aqueous solution: a combined study by quantum chemistry and molecular dynamics simulation.

The structures of aquo complexes of the curium(III) ion have been systematically studied using quantum chemical and molecular dynamics (MD) methods. The first hydration shell of the Cm3+ ion has been calculated using density functional theory (DFT), with and without inclusion of the conductor-like polarizable continuum medium (CPCM) model of solvation. The calculated results indicate that the primary hydration number of Cm3+ is nine, with a Cm-O bond distance of 2.

Multiconfigurational theoretical study of the octamethyldimetalates of Cr(II), Mo(II), W(II), and Re(III): revisiting the correlation between the M-M bond length and the delta --> delta* transition energy.

Four compounds containing metal-metal quadruple bonds, the [M2(CH3)8]n- ions (M = Cr, Mo, W, Re and n = 4, 4, 4, 2, respectively), have been studied theoretically using multiconfigurational quantum-chemical methods. The molecular structure of the ground state of these compounds has been determined and the energy of the delta --> delta* transition has been calculated and compared with previous experimental measurements. The high negative charges on the Cr, Mo, and W complexes lead to difficulties in the successful modeling of the ground-state structures, a problem that has been addressed by the explicit inclusion of four Li+ ions in these calculations.

Oxalate-bridged dinuclear M2 units: dimers of dimers, cyclotetramers, and extended sheets (m = Mo, W, Tc, Ru, and Rh).

The electronic structures of D(4h)-M(2)(O(2)CH)(4) and the oxalate-bridged complexes D(2h)-[(HCO(2))(3)M(2)](2)(mu-O(2)CCO(2)) and D(4h)-[(HCO(2))(2)M(2)](4)(mu-O(2)CCO(2))(4) have been investigated by a symmetry analysis of their MM and oxalate-based frontier orbitals, as well as by electronic structure calculations on the model formate complexes (M = Mo and W {d(4)-d(4)}, Tc, Ru {d(6)-d(6)}, and Rh {d(7)-d(7)}). Significant changes in the ordering, interactions, and electronic occupation of the molecular orbitals (MOs) arise through both the progression from d(4) to d(7) metals and the change from second to third row transition metals. For M = Mo and W, the highest-occupied orbitals are delta based, while the lowest-unoccupied orbitals are oxalate pi based; for M = Tc, the highest-occupied orbitals are an energetically tight delta-based set of MOs, while the lowest-unoccupied orbitals are MM-based pi.

Theoretical investigations of uranyl-ligand bonding: four- and five-coordinate uranyl cyanide, isocyanide, carbonyl, and hydroxide complexes.

The coordination and bonding of equatorial hydroxide, carbonyl, cyanide (CN-), and isocyanide (NC-) ligands with uranyl dication, [UO2]2+, has been studied using density functional theory with relativistic effective core potentials. Good agreement is seen between experimental and calculated geometries of [UO2(OH)4]2-. Newly predicted ground-state structures of [UO2(OH)5]3-, [UO2(CO)4]2+, [UO2(CO)5]2+, [UO2(CN)4]2-, [UO2(CN)5]3-, [UO2(NC)4]2-, and [UO2(NC)5]3- are reported.

Reactions of laser-ablated uranium atoms with H2O in excess argon: a matrix infrared and relativistic DFT investigation of uranium oxyhydrides.

Laser-ablated U atoms react with H2O during condensation in excess argon. Infrared absorptions at 1416.3, 1377.

On the electronic structure of molecular UO2 in the presence of Ar atoms: evidence for direct U-Ar bonding.

Calculations via scalar-relativistic density functional theory (DFT) and ab initio CCSD(T) methodologies are used to explore the possibility of direct interactions between molecular UO2 and Ar atoms. The 3Hg electronic state of UO2, which is an excited state of the isolated molecule, exhibits significant bonding to Ar in the model complexes UO2(Ar) and UO2(Ar)5. The calculated vibrational frequencies of ground-state 3Phiu UO2 and UO2(Ar)5 with an (fphi)1(fdelta)1 electron configuration agree well with the observed frequencies of UO2 in solid neon and solid argon, respectively.

On the noble-gas-induced intersystem crossing for the CUO molecule: experimental and theoretical investigations of CUO(Ng)n (Ng = Ar, Kr, Xe; n = 1, 2, 3, 4) complexes in solid neon.

Uranium atoms excited by laser ablation react with CO in excess neon to produce the novel CUO molecule, which forms distinct Ng complexes (Ng = Ar, Kr, Xe) when the heavier noble gases are added. The CUO(Ng) complexes are identified through CO isotopic and Ng substitution on the neon matrix infrared spectra and by comparison to DFT frequency calculations. The U-C and U-O stretching frequencies of CUO(Ng) complexes are slightly red-shifted from frequencies for the (1)Sigma(+) CUO ground state, which identifies singlet ground state CUO(Ng) complexes.

Bonding of multiple noble-gas atoms to CUO in solid neon: CUO(Ng)n (Ng=Ar, Kr, Xe; n=1, 2, 3, 4) complexes and the singlet-triplet crossover point.

Laser-ablated U atoms co-deposited with CO in excess neon produce the novel CUO molecule, which forms distinct Ng complexes (Ng=Ar, Kr, Xe) with the heavier noble gases. The CUO(Ng) complexes are identified through CO isotopic and Ng reagent substitution and comparison to results of DFT frequency calculations. The U[bond]C and U[bond]O stretching frequencies of CUO(Ng) complexes are slightly red-shifted from neon matrix (1)Sigma(+) CUO values, which indicates a (1)A' ground state for the CUO(Ng) complexes.

Spiers memorial lecture. The quantum chemistry of d- and f-element complexes: from an approximate existence to functional happiness.

The field of modern quantum inorganic chemistry is just over 50 years old, dating back to 1951, when quantitative LCAO molecular orbital theory was developed and ferrocene was discovered. This Lecture provides a survey of the development of the field through about 1980, which has led to its current state. The application of modern quantum chemical techniques are illustrated via two disparate examples from the authors' research group.

Noble gas-actinide complexes of the CUO molecule with multiple Ar, Kr, and Xe atoms in noble-gas matrices.

Laser-ablated U atoms react with CO in excess argon to produce CUO, which is trapped in a triplet state in solid argon at 7 K, based on agreement between observed and relativistic density functional theory (DFT) calculated isotopic frequencies ((12)C(16)O, (13)C(16)O, (12)C(18)O). This observation contrasts a recent neon matrix investigation, which trapped CUO in a linear singlet state calculated to be about 1 kcal/mol lower in energy. Experiments with krypton and xenon give results analogous to those with argon.

Perfluoroterephthalate bridged complexes with M-M quadruple bonds: ((t)BuCO(2))(3)M(2)(mu-O(2)CC(6)F(4)CO(2))M(2)(O(2)C(t)Bu)(3), where M = Mo or W. Studies of solid-state, molecular, and electronic structure and correlations with electronic and Raman spectral data.

The compounds [((t)BuCO(2))(3)M(2)(mu-O(2)CC(6)F(4)CO(2))M(2)(O(2)C(t)Bu)(3)], M(4)PFT, where M = Mo or W, are shown by model fitting of the powder X-ray diffraction data to have an infinite "twisted" structure involving M.O intermolecular interactions in the solid state. The dihedral angle between the M(2) units of each molecule is 54 degrees.

Noble gas-actinide compounds: evidence for the formation of distinct CUO(Ar)(4-n)(Xe)(n) and CUO(Ar)(4-n)(Kr)(n) (n = 1, 2, 3, 4) complexes.

Laser-ablated U atoms react with CO in excess argon to produce CUO, which gives rise to 852.5 and 804.3 cm-1 infrared absorptions for the triplet state CUO(Ar)n complex in solid argon at 7 K.

Experimental and theoretical studies of the products of laser-ablated thorium atom reactions with H2O in excess argon.

Reactions of laser-ablated Th atoms with H2O during condensation in excess argon have formed a variety of intriguing new Th, H, O species. Infrared absorptions at 1406.0 and 842.

Oxalate-bridged complexes of dimolybdenum and ditungsten supported by pivalate ligands: ((t)BuCO(2))(3)M(2)(mu-O(2)CCO(2))M(2)(O(2)C(t)Bu)(3). Correlation of the solid-state, molecular, and electronic structures with Raman, resonance Raman, and electronic spectral data.

The compounds ((t)BuCO(2))(3)M(2)(mu-O(2)CCO(2))M(2)(O(2)C(t)Bu)(3) (M(4)OXA), where M = Mo or W, are shown by analysis of powder X-ray diffraction data to have extended lattice structures wherein oxygen atoms from the oxalate and pivalate ligands of one M(4)OXA molecule are linked to metal atoms of neighboring molecules. Raman, resonance Raman, electronic absorption (2-325 K in 2-MeTHF), and emission spectra are reported, together with corresponding spectra of the mu-O(2)(13)C(13)CO(2) isotopomers. To aid in the assignment, the Raman spectra of K(2)C(2)O(4).

Noble gas-actinide compounds: complexation of the CUO molecule by Ar, Kr, and Xe atoms in noble gas matrices.

The CUO molecule, formed from the reaction of laser-ablated U atoms with CO in a noble gas, exhibits very different stretching frequencies in a solid argon matrix [804.3 and 852.5 wave numbers (cm(-1))] than in a solid neon matrix (872.

Spin-Orbit Effects, VSEPR Theory, and the Electronic Structures of Heavy and Superheavy Group IVA Hydrides and Group VIIIA Tetrafluorides. A Partial Role Reversal for Elements 114 and 118.

Relativistic effective core potentials and spin-orbit operators are used in relativistic configuration interaction calculations to explore the effects of spin-orbit coupling on the electronic structures of atoms and molecules of elements 114 and 118. The monohydrides of group IVA and the tetrafluorides of group VIIIA are examined in order to provide examples of trends within families among the various periods. The spin-orbit effect is found to play a dominant role in the determination of atomic and molecular properties.