In the ionic structure of the title compound, [Fe(C12H8N2)3](C9H5N4O2)2·H2O, the octahedral tris-chelate [Fe(phen)3](2+) dications [Fe-N = 1.9647 (14)-1.9769 (14) Å; phen is 1,10-phenathroline] afford one-dimensional chains by a series of slipped π-π stacking interactions [centroid-to-centroid distances = 3.792 (3) and 3.939 (3) Å]. The 1,1,3,3-tetracyano-2-(2-hydroxyethyl)propenide anions, denoted tcnoetOH(-), reveal an appreciable delocalization of π-electron density, involving the central propenide [C-C = 1.383 (3)-1.401 (2) Å] fragment and four nitrile groups, and this is also supported by density functional theory (DFT) calculations at the B97D/6-311+G(2d,2p) level. Primary noncovalent inter-moiety interactions comprise conventional O-H...O(N) and weak C-H...O(N) hydrogen bonding [O...O(N) = 2.833 (2)-3.289 (5) Å and C...O(N) = 3.132 (2)-3.439 (2) Å]. The double anion...π interaction involving a nitrile group of tcnoetOH(-) and two cis-positioned pyridine rings (`π-pocket') of [Fe(phen)3](2+) [N...centroid = 3.212 (2) and 3.418 (2) Å] suggest the relevance of anion...π stackings for charge-diffuse polycyanoanions and common M-chelate species.
Keywords: anion...π interactions; crystal structure; density functional theory (DFT) calculations; π-pocket.