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4, 4'-BIPYRIDINIUM HEXACYANOFERRATE(II) AND (III) HYDRATES

Hexacyanoferrates(II) and (III) (mostly their potassium salts) are often used as analytical reagents due to their easily conducted redox reactions and high stabilities under various conditions. In structural chemistry, though, they are of much greater importance and interest not only due to their ability to form extensive hydrogen bond networks, wherein hexacyanoferrate anions are usually hydrogen bond acceptors, but also because of their potential in making new solid electrolytes and metal-organic frameworks. In present research 4, 4'-bipyridinium hexacyanoferrate(II) tetrahydrate (I) and 4, 4'-bipyridinium 4-(pyrid-4-yl)pyridinium hexacyanoferrate(III) trihydrate (II) are prepared and their crystal structures determined by single crystal X-ray diffraction analysis. Compound I crystallizes as dark blue triclinic platelets (space group P , Z = 1) with iron atoms in inversion centers. Three structure determining hydrogen bond motifs are present (shown in Figure 1), chains of hexacyanoferrate(II) anions bridged by two water molecules per anion along the b axis, and chains of same anions, bridged by two 4, 4'-bipyridinium cations in two different directions, along the a axis and the [0 1 1] direction. Thus a 3D hydrogen bond network is formed. Compound II crystallizes as light yellow monoclinic needles (space group P21/c, Z = 4). In it's structure 4, 4'-bipyridine is present in two different forms, as double protonated 4, 4'-bipyridinium cations that, together with water molecules and hexacyanoferrate(III) anions form a complex 3D hydrogen bond network where N―H∙∙∙O, O―H∙∙∙N and O―H∙∙∙O hydrogen bonds are present, and wherein, along the a axis, channels are situated, and as single protonated 4-(pyrid-4-yl)pyridinium cations that form long N―H∙∙∙N hydrogen bonded chains inside the channels.

hexacyanoferates; crystal structure; hydrogen bonding

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