Probing Hydrogen Bond Networks in Half-Sandwich Ru(II) Building Blocks by a Combined ¹H DQ CRAMPS Solid-State NMR, XRPD, and DFT Approach

The hydrogen bond network of three polymorphs (1α, 1β, and 1γ) and one solvate form (1·H₂O) arising from the hydration–dehydration process of the Ru­(II) complex [(p-cymene)­Ru­(κN-INA)­Cl₂] (where INA is isonicotinic acid), has been ascertained by means of one-dimensional (1D) and two-dimensional (2D) double quantum ¹H CRAMPS (Combined Rotation and Multiple Pulses Sequences) and ¹³C CPMAS solid-state NMR experiments. The resolution improvement provided by homonuclear decoupling pulse sequences, with respect to fast MAS experiments, has been highlighted. The solid-state structure of 1γ has been fully characterized by combining X-ray powder diffraction (XRPD), solid-state NMR, and periodic plane-wave first-principles calculations. None of the forms show the expected supramolecular cyclic dimerization of the carboxylic functions of INA, because of the presence of Cl atoms as strong hydrogen bond (HB) acceptors. The hydration–dehydration process of the complex has been discussed in terms of structure and HB rearrangements.