The complexes [(C-N-C)MX(n)(thf)(m)] with the 'pincer' 2,6-bis(imidazolylidene)pyridine, (C-N-C) = 2,6-bis(arylimidazol-2-ylidene)pyridine, aryl = 2,6-Pr(i)2C6H3, M = V, X = Cl, n = 2, m = 1 1a; M = Cr, X = Cl, n = 2, m = 0, 2a, X = Br, 2b; M = Mn, X = Br, n = 2, m = 0, 3; M = Nb, X = Cl, n = 3, m = 0, 4; and M = U, X = Cl, n = 4, m = 0, 5, were synthesised by (a) substitution of labile tmed (1a), thf (2a, 3, 5) or dme (4) by free (C-N-C) or by (b) reaction of the bisimidazolium salt (CH-N-CH)Br2 with {Cr[N(SiMe3)2]2(thf)2} followed by amine elimination (2b). Attempted alkylation of 1a, 2, 3a and 4 with Grignard or alkyl lithiums gave intractable mixtures, and in one case [reaction of 1a with (mesityl)MgBr] resulted in exchange of Cl by Br (1b). Oxidation of 1a or [(C-N-C)VCl3] with 4-methylmorpholine N-oxide afforded the trans-V(C-N-C)(=O)Cl2, 6, which by reaction with AgBF4 in MeCN gave trans-[V(C-N-C)(=O)(MeCN)2][BF4]2, 7. Reaction of 1a with p-tolyl azide gave trans-V(C-N-C)(=N-p-tolyl)Cl2 8. The complex trans-Ti(C-N-C)(=NBu(t))Cl2, 9, was prepared by substitution of the pyridine ligands in Ti(NBu(t))Cl2(py)3 by C-N-C.

Barium sulfate is a common scale in oil production installations that is treated and controlled with phosphonate inhibitors. A fundamental understanding of how these inhibitors operate, however, is only slowly emerging. In this paper, we investigate the effect on barium sulfate crystallization of two very similar phosphonate molecules that only differ in their backbone spacing, ethylenediamine-N,N,N′,N′-tetra(methylenephosphonic acid) (EDTMP) and hexamethylenediamine-N,N,N′,N′-tetra(methylenephosphonic acid) (HDTMP). It was found that the inhibitory efficacy of the organic molecules depends on their structural differences but also on the presence of other cations such as Zn 2+ . It appears that both stereochemical considerations and complexation strength differences between the two phosphonate additives result in different inhibitory powers. In the presence of zinc cations and EDTMP, it is found that inhibition is related to the concentration of uncomplexed ("free") organic.

The effect of various benzoic acids on the precipitation of barite and calcite was investigated. The acids varied in the number of carboxylate groups, from di-benzoic acids (phthalic, isophthalic and terephthalic) through to the hexabenzoic acid (mellitic acid). It was found that the stereochemistry of the di-benzoic acids was important, as was the pH of the solution (trimesic acid was used as a test case and showed greatest inhibition was achieved with all carboxylate groups deprotonated). Interestingly, for both the calcite and barite systems, mellitic acid was found to be both a potent inhibitor and a significant crystal growth modifier. In the case of barite, the presence of mellitic acid produced nanoparticles that agglomerated. The nanoparticles were found to be ~20 nm in size from XRD linewidth analysis and 20-50nm from TEM. Humic acid was also tested and found to form bundled fibres of barium sulfate.

Dipositive cation substitution in sulfate minerals has been a topic of investigation both experimentally and computationally. Here the possibility of tripositive cation substitution with accompanying vacancy formation is considered, specifically lanthanum ion substitution in barium sulfate. Experimentally, the lanthanum ions impact “bulk” crystallization in a way that is best explained by considering the solution phase ion-pair interactions. However, morphological results suggest that lanthanum ions do more than impact the free sulfate levels. Atomic force microscopy results showed that both lanthanum and calcium ions are strong inhibitors of barite growth. X-ray diffraction on bulk samples showed that lanthanum ions do indeed incorporate, as determined by lattice parameter changes. Finally, computational modeling suggests that while calcium incorporation is more energetically favorable, lanthanum ions prefer to substitute on the surface more so than calcium ions.