Crystal structures of three anhydrous nitroprussides: M[Fe(CN)₅NO] (M=Mn, Zn, Cd)

Abstract

The crystal structures of Mn, Zn, and Cd nitroprussides in their anhydrous state, M͓Fe͑CN͒ 5 NO͔ ͑M =Mn,Zn,Cd͒, were refined from XRD powder patterns using the Rietveld method. These compounds have a porous framework useful for adsorption and storage of small molecules. Water crystallization can be removed by heating below 100°C without disrupting the 3D network by introducing certain structural modification mainly around the M site ͑Mn, Zn, Cd͒. For M = Mn and Cd, the compounds were found to be orthorhombic with space group Pnma ͓Mn: a = 13.7844͑1͒, b = 7.3750͑2͒, c = 10.9470͑2͒ Å, V = 1112.8͑1͒ Å 3 , Z =4; Cd:a = 13.9566͑3͒, b = 7.5040͑4͒, c = 11.0230͑2͒ Å, V = 1154.4͑1͒ Å 3 , Z =4͔. Anhydrous zinc nitroprusside crystallizes in rhombohedral with space group R3 ͓a = b = 19.2525͑1͒ , c = 17.7107͑2͒ Å,␥ = 120.0°, V = 5685.1͑1͒ Å 3 , Z =18͔. When exposed to humid air, these anhydrous compounds become hydrated. The XRD powder patterns were recorded under vacuum on samples dehydrated in situ. The structural information from XRD was complemented with thermo-gravimetric, infrared, and Mössbauer data. © 2007 International Centre for Diffraction Data.

Hydrogen Storage in Porous Transition Metals Nitroprussides

“…The obtained spectral parameters are available from the Supporting Information. The estimated values for the Mössbauer parameters and the observed frequencies for ν(CN) and ν(NO) vibrations in the IR spectra reproduce those results already reported for divalent transition metal nitroprussides. – Mössbauer spectra of nitroprussides reveal that the electronic structure of this family of compounds is dominated by the bonding properties of the NO group …”

“…The XRD powder patterns for this series correspond to the reported crystal structures for the hydrated phases of divalent transition metals nitroprussides: Mn and Cd (orthorhombic, Pnma ); Cu (orthorhombic, Amm 2); Fe, Co, and Ni (cubic, Fm 3̅ m ); and Zn (rhombohedral, R 3̅). – For adsorption studies these compounds must be dehydrated in order to liberate the available free space in the structure from water molecules. The crystal structures for the anhydrous phases of this series of compounds are known. – Except for Cu, upon water removal the material framework is preserved with certain cell contraction, which for cubic phases is the largest, and amounts to 2% of cell volume reduction . For Cu, the water removal leads to a structural transformation to form a tetragonal phase also of porous nature .…”

“…In the hydrated phases these available coordination sites are occupied by coordinated waters. For the orthorhombic phases (Mn, Cd), neighboring building blocks are accommodated maintaining antiparallel their NO groups, whereas the axial cyanide behaves as a bridge group shared by the two metal centers (Figure ) . From such an arrangement of building units, a ripple sheet framework results.…”

“…These channels have a hydrophilic surface because of the unsaturated coordination sphere for the metal situated at the channels surface. For zinc, the building units are accommodated in such a way that six NO groups of neighboring blocks form a hexagonal opening of about 4 Å (diameter) . Two of these NO openings delimit an ellipsoidal cavity of about 15 × 10.35 Å (Figure ).…”

Topological Motifs in Cyanometallates: From Building Units to Three-Periodic Frameworks

“…In particular, nitroprusside [Fe­(CN) 5 NO] 2– ion falls into this category and results in 5-coordinated underlying nets of a noy topology in [{Fe­(H 2 O)}­{Fe­(CN) 5 (NO)}]·2H 2 O [71228], [{Mn­(H 2 O)}­{Fe­(CN) 5 (NO)}]·2H 2 O 69137], [ M {Fe­(CN) 5 NO}] (M = Cd, Pb, Mn) [109420, 152063, 109421] , (Figure left, middle) and other complexes. This net is known to be related to pcu , which is characteristic for the Prussian Blue analogues (Figures top, right).…”