New 3d–4f supramolecular systems constructed by [Fe(bipy)(CN)4]− and partially blocked lanthanide cations

The reaction of acetonitrile (1–5) and mixed acetonitrile/water 1:1 (6–9) solutions containing the cyanide-bearing [Fe(bipy)(CN)4]− building block (bipy = 2,2′-bipyridine) and the partially blocked [Ln(bpym)]3+ cation (Ln = lanthanide trivalent cation and bpym = 2,2′-bipyrimidine) has afforded two new families of 3d–4f supramolecular assemblies of formula [Ln(bpym)(NO3)2(H2O)3][Fe(bipy)(CN)4] · H2O · CH3CN [Ln = Sm (1), Gd (2), Tb (3), Dy (4) and Ho (5)] and [Ln(bpym)(NO3)2(H2O)4][Fe(bipy)(CN)4] [Ln = Pr (6), Nd (7), Sm (8), Gd (9)]. They crystallize in the P21/c (1–5) and P2/c (6–9) space groups and their structures are made up of [Fe(bipy)(CN)4]− anions (1–9) and [Ln(bpym)(NO3)2(H2O)n]+ cations [n = 3 (1–5) and 4 (6–9)] with uncoordinated water and acetonitrile molecules (1–5) which are interlinked through an extensive network of hydrogen bonds and π–π stacking into three-dimensional motifs. Both families have in common the occurrence of the low-spin iron(III) unit [Fe(bipy)(CN)4]− where two bipy–nitrogen and four cyanide–carbon atoms build a somewhat distorted octahedral surrounding around the iron atom [Fe–N = 1.980(3)–1.988(3) Å (1–5) and 1.988(2)–1.992(2) Å (6–9); Fe–C = 1.904(5)–1.952(4) Å (1–5) and 1.911(2)–1.948(3) Å (6–9)]. The main structural difference between both families concerns the environment of the lanthanide atom which is nine- (1–5)/10-coordinated (6–9) with a chelating bpym, two bidentate nitrate and three (1–5)/four (6–9) water molecules building distorted monocapped (1–5)/bicapped (6–9) square antiprisms. This different lanthanide environment is at the origin of the different hydrogen bonding pattern of the two families of compounds.

The two different 3D supramolecular arrangements in the 3d–4f isostructural series [Fe(bipy)(CN)4][Ln(bpym)(NO3)2(H2O)3] · H2O · CH3CN [Ln = Sm (1), Gd (2), Tb (3), Dy (4) and Ho (5)] (left) and [Fe(bipy)(CN)4][Ln(bpym)(NO3)2(H2O)4] [Ln = Pr (6), Nd (7), Sm (8) and Gd (9)] (right) are dictated by the lanthanide geometry (mono- or bicapped square antiprism) which is in turn influenced by the nature of the solvent used in the synthesis and the distinct ionic radii of the trivalent rare-earth ions.Figure optionsDownload as PowerPoint slide