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The effects of graphene oxide (GO) on the early-age hydration process and mechanical properties of Portland cement paste were experimentally investigated in this study. Based on an isothermal calorimeter measurement, the hydration rate of cement was observed to increase with the increase of GO content by nucleation effect. On the other hand, the electrical resistivity development of GO-cement paste was monitored using a non-contact electrical resistivity device. The result showed that electrical the resistivity of GO-cement paste was evidently higher than that of plain cement paste. However, cement paste with excessive amounts of GO exhibited a decreased electrical resistivity due to the massive ion diffusion caused by GO. Compared to plain cement paste, the GO-cement paste exhibited obviously higher compressive and flexural strengths, but the enhancements in compressive strength began to decline when the GO amount was greater than 0.04%. The microstructure characterization indicated that GO can apparently densify the cement pastes with less porosity and hydrates networking, which is consistent with the results of hydration acceleration and strength enhancement. © 2017 Elsevier Ltd

Zr(NR2)2[MeC(NiPr)2]2 (R = Me, 1; Et, 2) have been prepared through aminolysis and their reactions with O2 and water have been studied. Two major products from the reactions are the oxo dimer {(μ-O)Zr[MeC(NiPr)2]2}2 (3) and its insoluble polymer {(μ-O)Zr[MeC(NiPr)2]2}n (4). Over time the dimer 3 polymerizes to 4. Zr peroxo trimer {(μ-η2:η2-O2)Zr[MeC(NiPr)2]2}3 (5) was also observed from the reaction of 1 with O2 and its crystal structure is reported. DFT calculations show that the reaction of 1 with O2 follows a radical process, yielding the peroxo trimer 5. Mass spectrometric studies of the reactions of water in air with 1 and 2 show the formation of the oxo monomer (O=)Zr[MeC(NiPr)2]2 (6), oxo dimer {(μ-O)Zr[MeC(NiPr)2]2}2 (3), and the dihydroxy monomer (HO)2Zr[MeC(NiPr)2]2 (7). In addition, the cations {Zr(NR2)[MeC(NiPr)2]2}+ (R = Me, Et) were observed. 2 revealed an interesting dynamic NMR behavior. Variableerature (VT) NMR spectroscopy has been used to study the Bailar twist process in 2, giving activation parameters ΔH‡ = 10.9(1.1) kcal mol-1, ΔS‡ = -11(4) eu and ΔG‡ 303 K = 14(2) kcal mol-1. © 2015 Elsevier Ltd. All rights reserved.

(Me2N)(4)Ta-(SiBuPh2)-Ph-t (1) reacts with O-2 to give (Me2N)(4)Ta((OSiBuPh2)-Ph-t) (2), (Me2N)(3)Ta(ONMe2)((OSiBuPh2)-Ph-t) (3), and the unusualy-oxo amino (Me2N)(2)((Ph2BuSiO)-Si-t)(2)(mu,eta(2)-Me2NCH2NMe)(2)Ta-2(mu-O)(2) (4) containing two bridging chelating (aminomethyl)am ides -N(Me)CH2NMe2. The dimer 4 was characterized by X-ray crystallography. 2 also reacts with 02 to give both 3 and 4. Reaction pathways in the formation of these complexes are discussed. In reactions of O-2 with d(0) 1 and 2, oxidation of the ligands is the prevailing pathway.

Reactions of MCl5 (M = Nb, Ta) with LiNMe2 have been found to yield M(NMe2)(4)(eta(2)-MeNCH2NMe2) (M = Nb, 2a; Ta, 2b) containing a chelating ligand (dimethylaminomethylene)methylamide, as confirmed by NMR spectroscopy, DFT calculations, and their reactivity studies.

Reaction of d(0) Ta(NMe2)(5) (1) with O-2 yields two aminoxy complexes (Me2N)(n)Ta(eta(2)-ONMe2)(5-n) (n = 4, 2; 3, 3) as well as (Me2N)(4)Ta-2[eta(2)-N(Me)CH2NMe2](2)(mu-O)(2) (4) and (Me2N)(6)Ta-3[eta(2)-N(Me)CH2NMe2](2)-(eta(2)-ONMe2)(mu-O)(3) (5) containing novel chelating (aminomethyl)amide-N(Me)CH2NMe2 ligands. The crystal structures of 2-5 have been determined by X-ray crystallography. (Me2N)(4)Ta(eta(2)-ONMe2) (2) converts to (Me2N)(3)Ta(eta(2)-ONMe2)(2) (3) in its reaction with O-2. In addition, the reaction of Ta(NMe2)(5) with 3 gives 2 only at elevated temperatures. Density functional theory (DIFT) calculations have been used to investigate the mechanistic pathways in the reactions of Ta(NMe2)(5) (1) with triplet O-2-Monomeric reaction pathways in the formation of 2-5 are proposed. A key step is the oxygen insertion into a Ta-N bond in 1 through an intersystem conversion from triplet to singlet energy surface to give an active peroxide complex (Me2N)(4)-Ta(eta(2)-O-O-NMe2) (A4). The DFT studies indicate that the peroxide ligand plays an important role, including oxidizing an amide to an imine ligand through the abstraction of a hydride. Insertion of Me-N=CH2 into a Ta-amide bond yields the unusual -N(Me)CH2NMe2 ligands.