Most Cited Hydrate Paper

The most cited paper on a crystalline hydrate is a report from 1948 entitled "Nuclear Resonance Absorption in Hydrated Crystals: Fine Structure of the Proton Line" published in the Journal of Chemical Physics. While it has been cited over 1100 times, this paper actually isn't about organic or pharmaceutical hydrates at all but about an inorganic material, gypsum (CaSO4.2H2O) - something we might call a water coordination complex, aquo complex or hydrated metal complex. Gypsum is a hugely well known material of course found in alabaster, platerboard, cement and fertilizer. While the X-ray crystal structure of gypsum was published in 1936, it was not known with significant precision until 1974, this much earlier NMR study allowed the measurement of the H...H distance in the water molecules coordinated to the calcium ion by means of fine structure observed in the NMR data determined on a single crystal. Moreover, the variation of this peak splitting with field direction allowed the determination of the orientation of the line joining protons in the water molecule. The result was deemed consistent with "positions ascribed to hydrogen nuclei in the lattice through simple considerations of chemical bonding" - an early illustration of alternative structure determination techniques.