Bimetallic Cyanide-Bridged Complexes Based on the Photochromic Nitroprusside Anion and Paramagnetic Metal Complexes. Syntheses, Structures, and Physical Characterization of the Coordination Compounds [Ni(en)₂]₄[Fe(CN)₅NO]₂[Fe(CN)₆]·5H₂O, [Ni(en)₂][Fe(CN)₅NO]·3H₂O, [Mn(3-MeOsalen)(H₂O)]₂[Fe(CN)₅NO], and [Mn(5-Brsalen)]₂[Fe(CN)₅NO]

Abstract

The synthesis, crystal structure, and physical characterization of the coordination compounds [Ni(en) 2 ] 4 [Fe(CN) 5 NO] 2 [Fe(CN) 6 ]·5H 2 O ( 1 ), [Ni(en) 2 ][Fe(CN) 5 NO]·3H 2 O ( 2 ), [Mn(3-MeOsalen)(H 2 O)] 2 [Fe(CN) 5 NO] ( 3 ), and [Mn(5-Brsalen)] 2 [Fe(CN) 5 NO] ( 4 ) are presented. 1 crystallizes in the monoclinic space group P 2 1 / n ( a = 7.407(4) Å, b = 28.963(6) Å, c = 14.744(5) Å, α = 90°, β = 103.26(4)°, γ = 90°, Z = 2). Its structure consists of branched linear chains formed by cis -[Ni(en) 2 ] 2+ cations and ferrocyanide and nitroprusside anions. The presence of two kinds of iron(II) sites has been demonstrated by Mössbauer spectroscopy. 2 crystallizes in the monoclinic space group P 2 1 / c ( a = 11.076(3) Å, b = 10.983(2) Å, c = 17.018(5) Å, α = 90°, β = 107.25(2)°, γ = 90°, Z = 4). Its structure consists of zigzag chains formed by an alternated array of cis -[Ni(en) 2 ] 2+ cations and nitroprusside anions. 3 crystallizes in the triclinic space group P 1̄ ( a = 8.896(5) Å, b = 10.430(5) Å, c = 12.699(5) Å, α = 71.110(5)°, β = 79.990(5)°, γ = 89.470(5)°, Z = 1). Its structure comprises neutral trinuclear bimetallic complexes in which a central [Fe(CN) 5 NO] 2 - anion is linked to two [Mn(3-MeOsalen)] + cations. 4 crystallizes in the tetragonal space group P 4/ ncc ( a = 13.630(5) Å, c = 21.420(8) Å, Z = 4). Its structure shows an extended 2D neutral network formed by cyclic octameric [−Mn−NC−Fe−CN−] 4 units. The magnetic properties of these compounds indicate the presence of quasi-isolated paramagnetic Ni 2+ and Mn 3+ . Irradiated samples of the four compounds have been studied by differential scanning calorimetry to detect the existence of the long-lived metastable states of nitroprusside.