Water‐Soluble (Pterin)rhenium(I) Complex: Synthesis, Structural Characterization, and Two Reversible Protonation–Deprotonation Behavior in Aqueous Solutions

Abstract A new water‐soluble complex, Re(CO) 3 (pterin)(H 2 O), was synthesized and characterized by 1 H NMR and FTIR spectroscopy, and by a combination of three mass spectrometry techniques: MALDI, probe electrospray ionisation (PESI), and ESI. Because, unlike most metal‐pterin complexes, the Re I complex is quite soluble in water, appropriate single crystals could be obtained for structural X‐ray analysis. We report here the first solid state molecular structure containing a pterin ligand coordinated to the Re(CO) 3 core. This determination revealed that strong H bonds between the hydrogen atom of the 2‐amino group and crystallization water molecules give rise to a polymeric arrangement of Re(CO) 3 (pterin)(H 2 O) complexes in the lattice. Protonation studies in aqueous solutions of the Re I complex showed two acid‐base equilibriums with p K a1 = 3.9 and p K a2 = 8.8. p K a1 was assigned to the protonation equilibrium at N3 of the pterin ligand in the complex and p K a2 could be ascribed to the deprotonation of a coordinated water molecule.

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