The crystal structures of eight new copper chloride coordination complexes with substituted pyridines have been determined through a combination of single crystal X-ray diffraction and ab initio structure solution from X-ray powder diffraction data. The polymeric compounds [CuCl2(INAc)(2)](n) (1), [CuCl2(INAm)(2)](n), (2), and [CuCl2(NAm)(2)](n), (3) (INAc = isonicotinic acid; INAm = isonicotinamide; NAm = nicotinamide) consist of chains of CuCl4 edge-sharing rhombi decorated by the pyridine-based ligands. All three compounds display similar hydrogen bonding interactions but differ in the arrangement of the polymeric chains. 1, 2, and 3 react reversibly with hydrochloric acid in solution/vapor form to produce the corresponding tetrachlorocuprate salts [CuCl4](H-INAc)(2)(H2O) (4a), [CuCl4](H-INAc)(2) (4b), [CuCl4] (H-INAm)(2) (form I/form II 5a/5b), and [CuCl4] (H-NAm)(2) (form I/form II 6a/6b). 4a exhibits discrete square planar [CuCl4](2-) ions, whereas the Cu in 4b, 5a, and 5b is in a 4 + 2 coordination. All four compounds display hydrogen bonding arrangements similar to those found in 1 and 2. 6a and 6b differ substantially from these compounds in both the hydrogen bonding contacts and the coordination geometry of the cuprate ion (flattened tetrahedral), though they differ from each other only in the orientation of the amide groups and packing arrangements. The formation of 6a/6b depends on the configuration of nicotinamide in the starting material.

Lacustrine carbonate deposits with spherulitic facies are poorly understood, but are key to understanding the economically important “Pre-Salt” Mesozoic strata of the South Atlantic. A major barrier to research into these unique and spectacular facies is the lack of good lacustrine spherulite-dominated deposits which are known in outcrop. Stratigraphy and petrography suggest one of the best analogue systems is found in the Carboniferous of Scotland: the East Kirkton Limestone. Here we propose a hydrogeochemical model that explains why the CaCO3, SiO2, Mg-Si-Al mineral suite associated with spherular radial calcite facies forms in alkaline lakes above basaltic bedrock. Demonstrating links between igneous bedrock chemistry, lake and spring water chemistry and mineral precipitation, this model has implications for studies of lacustrine sediments in rift basins of all ages. Using empirical and theoretical approaches, we analyze the relationship between metal mobilization from sub-surface volcaniclastic rocks and the potential for precipitation of carbonate minerals, various Mg-bearing minerals and chalcedony in a lacustrine spherulitic carbonate setting. This suite of minerals is most likely formed by in-gassing of CO2 to a carbon-limited alkaline spring water, consistent with the reaction of alkali igneous rocks in the subsurface with meteoric groundwater. We suggest that an analogous system to that at East Kirkton caused development of the ‘Pre-Salt’ spherulitic carbonate deposits.

The hydrochloride salt of isonicotinamide, C6H7N2O+·Cl−, has been synthesized from a dilute solution of hydrochloric acid in acetonitrile. The compound displays monoclinic symmetry (space groupC2/c) at 150 K, similar to the related hydrochloride salt of nicotinamide. The asymmetric unit contains one protonated isonicotinamide molecule and a chloride anion. An array of hydrogen-bonding interactions, including a peculiar bifurcated pyridinium–chloride interaction, results in linear chains running almost perpendicularly in the [150] and [1-50] directions within the structure. A description of the hydrogen-bonding network and comparison with similar compounds are presented.

The origin of spherical-radial calcite bodies – spherulites – in sublacustrine, hyperalkaline and saline systems is unclear, and therefore their palaeoenvironmental significance as allochems is disputed. Here, we experimentally investigate two hypotheses concerning the origin of spherulites. The first is that spherulites precipitate from solutions super-saturated with respect to magnesium-silicate clays, such as stevensite. The second is that spherulite precipitation happens in the presence of dissolved, organic acid molecules. In both cases, experiments were performed under sterile conditions using large batches of a synthetic and cell-free solution replicating waters found in hyperalkaline, saline lakes (such as Mono Lake, California). Our experimental results show that a highly alkaline and highly saline solution supersaturated with respect to calcite (control solution) will precipitate euhedral to subhedral rhombic and trigonal bladed calcite crystals. The same solution supersaturated with respect to stevensite precipitates sheet-like stevensite crystals rather than a gel, and calcite precipitation is reduced by ~50% compared to the control solution, producing a mixture of patchy prismatic subhedral to euhedral, and minor needle-like, calcite crystals. Enhanced magnesium concentration in solution is the likely the cause of decreased volumes of calcite precipitation, as this raised equilibrium ion activity ratio in the solution. On the other hand, when alginic acid was present then the result was widespread development of micron-size calcium carbonate spherulite bodies. With further growth time, but falling supersaturation, these spherules fused into botryoidal-topped crusts made of micron-size fibro-radial calcite crystals. We conclude that the simplest tested mechanism to deposit significant spherical-radial calcite bodies is to begin with a strongly supersaturated solution that contains specific but environmentally-common organic acids. Furthermore, we found that this morphology is not a universal consequence of having organic acids dissolved in the solution, but rather spherulite development requires specific binding behaviour. Finally, we found that the location of calcite precipitation was altered from the air:water interface to the surface of the glassware when organic acids were present, implying that attached calcite precipitates reflect precipitation via metal–organic intermediaries, rather than direct forcing via gas exchange.