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© 2018 Elsevier B.V. The syntheses, characterizations and structures of three novel dichloro(bis{2-[1-(4-methoxyphenyl)-1H-1,2,3-triazol-4-yl-κN 3 ]pyridine-κN})metal(II), [M(L) 2 Cl 2 ], complexes (metal = Mn, Co and Ni) are presented. In the solid state the molecules are arranged in infinite hydrogen-bonded 3D supramolecular structures, further stabilized by weak intermolecular π…π interactions. The DFT results for all the different spin states and isomers of dichloro(bis{2-[1-phenyl-1H-1,2,3-triazol-4-yl-κN 3 ]pyridine-κN})metal(II) complexes, [M(L 1 ) 2 Cl 2 ], support experimental measurements, namely that (i) d 5 [Mn(L 1 ) 2 Cl 2 ] is high spin with S = 5/2; (ii) d 7 [Co(L 1 ) 2 Cl 2 ] has a spin state of S = 3/2, (iii) d 8 [Ni(L 1 ) 2 Cl 2 ] has a spin state of S = 1; and (iv) for all [M(L 1 ) 2 Cl 2 ] and [M(L) 2 Cl 2 ] comple xes, with M = Mn, Co and Ni, the cis-cis-trans and the trans-trans-trans isomers, with the pyridyl groups trans to each other, have the lowest energy.

The South African National Research Foundation and the Central Research Fund of the University of the Free State, Bloemfontein, South Africa.

The synthesis, density functional theory (DFT) conformational study and structure analysis of novel two-legged piano stool Ni N-heterocyclic carbene (NHC) complexes and square planar Ni bis-N-heterocyclic carbene complexes, all containing either bromido- or thiophenolato ligands, are described. [CpNi(SPh)(NHC)] complexes were obtained from the neutral 18-electron [CpNiBr(NHC)] complexes by substitution of a bromido ligand with SPh, using NEt3 as a base to abstract the proton of HSPh. The 16-electron biscarbene complexes [Ni(SPh)2{NHC}2] were isolated when an excess of HSPh was added to the reaction mixture. Biscarbene complexes of the type [NiBr2(NHC)2] were obtained in the reaction of NiCp2 with a slight excess of the specific imidazolium bromide salt. The molecular and electronic structures of the mono- and bis-N-heterocyclic carbene complexes have been analysed using single crystal diffraction and density functional theory (DFT) calculations, to give insight into their structural properties.

The Norwegian Supercomputing Program (NOTUR) through a grant of computer time (Grant No. NN4654K) (JC), the South African National Research Foundation (JC, ML) and the Central Research Fund of the University of the Free State, Bloemfontein (JC) and the University of Pretoria (ML).

The synthesis and selected crystal structures of a series of nine (eight are reported for the first time) Mo(0) Fischer carbene complexes of the formula [(CO) 3 (L,L′)Mo C(Y)(2-furyl)] with Y = OEt, NH 2 or NHCy; L,L′ = CO,CO; PPh 3 ,CO; dppe (1,2-bis(diphenylphosphino)ethane) are reported. DFT quantum chemical calculations on the different possible isomers and conformers of the Mo carbene complexes yielded more than one stable conformation for each complex. The small energy difference between some of the conformers of the same complex indicates that in some cases more than one conformer should be experimentally feasible. The crystal structures of the complexes in the solid state correspond favourably with the DFT calculated structures. Natural bond orbital second-order perturbation theory calculations indicated donor–acceptor interactions between a furyl oxygen lone pair and the antibonding orbital of the N H for the Mo aminocarbene complexes, in agreement with the preference for the syn conformation for the Mo aminocarbene complexes in the solid state structures.

Cellulose is known to have wide industrial applications because of its natural abundance and possibility of enhancing its physical properties through modification with crosslinkers. This study considers the impacts of the difunctional long chain and multifunctional epoxy crosslinkers. Strong agreement was observed between the computed and experimental properties which include low porosity, higher network, compactness and elasticity of multifunctional over the difunctional long-chain epoxy modified cellulose (called hydrogels). These consequentially affect the dynamic fluctuation of cellulose, plasticity, glass temperature, viscosity and conductivity. Hydrogels that were experimentally found to have higher porosity, swelling and loading ability were also observed to have stronger water interaction and gas absorption. The multivariance analysis and partial least squares (PLS) established a good relationship between the experimental and computational results. The general order of gases diffusion through the hydrogels is N2 > CH4 > O2 > CO2 with some slight variation in the specific hydrogels.

South African National Research Foundation and the Central Research Fund of the University of the Free State, Bloemfontein, South Africa.

Norwegian Supercomputing Program (NOTUR) (Grant No. NN4654K), the South African National Research Foundation and the Central Research Fund of the University of the Free State, Bloemfontein.

Mononuclear Ti(β-diketonato)2Cl2 complexes with CF3-containing β-diketonato ligands, exhibit a monomer-hydrolysed dinuclear complex equilibrium when dissolved in CDCl3 containing trace amounts of water. This result is in contrast to the more electron rich derivatives with non CF3-containing β-diketonato ligands, for example, Ti(acac)2Cl2, which exsists only as the monomer in CDCl3 solution. The X-ray structure of the μ-oxo bridged hydrolysed dinuclear complex {Ti(CF3COCHCOCH3)2Cl}2(μ-O) reveals that the two mononuclear Ti units forming the dinuclear structure, both adopt a cis-trans-cis configuration with the CF3 groups of the trifluoroacetylacetonate ligands in trans positions. In solution both mononuclear Ti(β-diketonato)2Cl2 and hydrolysed dinuclear {Ti(β-diketonato)2Cl}2(μ-O) complexes exist as equilibrium mixtures of isomers. DFT calculations, used to determine the stability of the isomers, showed that for monomeric bis(β-diketonato)-titanium(IV) complexes, there is agreement with experimental solid state structures, in that the most stable DFT calculated isomer, of a specific complex, formed in the solid state. However for the dinuclear {Ti(CF3COCHCOCH3)2Cl}2(μ-O) complex, DFT calculations revealed that although most of the 10 isomers are experimentally possible due to the small energy difference obtained between the isomers, an isomer of higher energy formed in the solid state, suggesting that the equilibrium reaction between the monomer and hydrolysed dinuclear complex may contribute to the formation of the less stable dinuclear isomer {Ti(CF3COCHCOCH3)2Cl}2(μ-O) (1111).

The synthesis, structure and density functional theory (DFT) calculations of two novel Ga(III) complexes, the first containing a tetradentate Schiff base ligand (L1) and the second containing a tetradentate carboxamide ligand (L2), are presented. The complexes are isolated as octahedral complexes with two water molecules attached to the axial positions. Both experimental and DFT calculations show that when [Ga(L1)(H2O)2].NO3 is dissolved in dimethyl sulfoxide (DMSO), spontaneous substitution of axial water groups by DMSO occur to form [Ga(L1)(DMSO)2].NO3.

A conformation analysis of all possible isomers of 22 differently substituted 1,5-bis(phenyl)-3-nitroformazans is presented. Results clearly showed that, except for 1,5-bis(m-OPh-phenyl)-3-nitroformazan, the closed ring trans-syn, s-cis isomer (DD) is preferred. This result agrees with available experimental structures of differently substituted 1,5-bis(phenyl)-3-nitroformazans that all exhibit the closed ring trans-syn, s-cis conformation. The preference for the closed ring trans-syn, s-cis conformation was further explored by natural bond orbital and quantum theory of atoms in molecules analysis. It was hereby shown that the donor-acceptor interaction and electron density of the bond path related to the intramolecular N–H⋯N hydrogen bond in the closed ring trans-syn, s-cis isomer (DD) is stronger and larger respectively than in other isomeric forms such as the open trans-syn, s-trans (UD and DU) and linear trans-anti, s-trans (UU) configurations.

An X-ray study was conducted on tris(trifluoroacetylacetonato)-manganese(III). The two different molecules in the unit cell exhibit a distorted octahedral geometry and moderate compression Jahn–Teller distortion respectively. A number of F⋯H and F⋯F intermolecular interactions were observed in the packing of the crystals in the solid state. The crystal packing effects could lead to the observed compressed Jahn–Teller distortion, instead of the expected elongation Jahn–Teller distortion. A Quantum Theory of Atoms in Molecules (QTAIM) study on selected molecular pairs identified intermolecular bond paths (BP) between fluorine atoms with bond critical points (BCP) which have positive electron density (ρ) and Laplacian of electron density (∇2ρ) values, which are indicative of weak F···F non-covalent bonding interactions.

To date, only the trans isomers of [Cu(β-diketonato)2] complexes are isolated in the solid state. Both experimental solid state structures and density functional theory (DFT) calculations show that for [Cu(CF3COCHCO(C4H3X))2] complexes, the trans-2 conformer with X pointing towards the methine H of the β-diketonato ligand is obtained when X = O (complex 1). However, for X = S (complex 2), the trans-1 conformer with X pointing away from the methine H of the β-diketonato ligand, as well as the trans-2 conformer are possible, with trans-1 as the main conformer. A natural bond orbital (NBO) study provided new insights into the preferred orientation of the C4H3X group with respect to both the Cu(II) central atom and the β-diketonato ligand in [Cu(CF3COCHCO(C4H3X))2] complexes.

Norwegian Supercomputing Program (NOTUR) through a grant of computer time (Grant No. NN4654K).The South African National Research Foundation, HPC Warehouse Facility.The Central Research Fund of the University of the Free State, Bloemfontein and the University of Pretoria.

The synthesis and selected crystal structures of novel (M = Cr or Mo) and known (M = W) [(CO) 4 (PPh 3 )M = C(OEt)R] complexes, M = Cr, R = 2-thienyl ( 1 ), 2-furyl ( 2 ); M = Mo, R = 2-thienyl ( 3 ), 2-furyl ( 4 ); M = W, R = 2-thienyl ( 5 ), 2-furyl ( 6 ), are presented. Experimental crystal structures and DFT calculations of selected trans- and cis- triphenylphosphine-substituted Fischer carbene complexes, illustrate that the minimum energy conformation of triphenylphosphine (PPh 3 ) in octahedral [(CO) 4 (PPh 3 )ML]-complexes generally have distinct features that can be described in terms of the “ plane of nadir energy ”, a plane linking all points of minimum steric compression between the ligands. The generally observed orientation of PPh 3 involves a correlated feathering of the phenyl groups with the P C ipso bond of one phenyl group orientated near parallel to the nadir plane, and a meta carbon (C m ) of the other two phenyl groups orientated as near as possible to the nadir plane, orthogonal to the first. Although the orientation of PPh 3 in 6 - trans , [(CO) 4 (PPh 3 )W = C(OEt)2-furyl], deviates from this, DFT correctly calculated the unexpected and not generally observed PPh 3 orientation.

Different rhodium(I)/(III) diphenyl-2-pyridylphosphine complexes were isolated and successfully characterized. The [Rh(acac)(CO)(DPP)] (DPP = diphenyl-2-pyridylphosphine) complex crystallizes in the P 1 ¯ space group with four molecules per unit cell. The results clearly show that the differences between the two independent molecules are mainly centered around the orientation of the pyridyl ring within the two square planer molecules. The results also indicate that the phosphine ligands act as monodentate ligands in both molecules, with Rh–P and Rh–CO bond distances of 2.243(1); 2.235(1) and 1.791(4); 1.776(4) A respectively. A comparison of the ν(CO) stretching frequencies of a relatively large number of rhodium complexes indicated little overlap between the ν(CO) of different types of complexes (e.g. Rh(I) vs Rh(III)) and relatively small standard deviations within each type of complex. DFT calculations were used to determine the preferred pyridyl ring orientation. These calculations indicated that at least 12 areas of minimum energy, which exists as broad, low energy wells, are theoretically suitable for DPP group orientation within this kind of structure.