The first photochromic bimetallic assemblies based on Mn(III) and Mn(II) Schiff-base (salpn, dapsc) complexes and pentacyanonitrosylferrate

Four cyano-bridged bimetallic complexes, {[Mn(salpn)]2[Fe(CN)5NO]}n (1), {[Mn(salpn)(CH3OH)]4[Mn(CN)5NO]}[C(CN)3]·3H2O (2), {[Mn(dapsc)][Fe(CN)5NO]·0.5CH3OH·0.25H2O}n (3) and {[Mn(salpn)(CH3OH)]4[Fe(CN)5NO]}(ClO4)2·4H2O (4), where salpn2− = N,N′-1,3-propylene-bis(salicylideneiminato) dianion and dapsc = 2,6-diacetylpyridine-bis(semicarbazone), have been synthesized and structurally characterized by single crystal X-ray diffraction. In 1, the nitroprusside anion [Fe(CN)5NO]2− coordinates with four [Mn(salpn)]+via four co-planar CN− groups, whereas each [Mn(salpn)]+ links two [Fe(CN)5NO]2− ions, which results in a two-dimensional network. The structure of 3 contains two independent neutral infinite chains {[Mn(dapsc)][Fe(CN)5(NO)]}∞ consisting of alternating cationic [MnII(dapsc)]2+ and anionic [FeII(CN)5(NO)]2− units connected through cyanide bridges. The cation complexes 2 and 4 have a pentanuclear molecular structure in which four [Mn(salpn)(MeOH)]+ fragments are linked by the [Mn(CN)5NO]3− or [Fe(CN)5(NO)]2− moieties, respectively. The magnetic and photochromic properties of 1 and 3 have been studied. The thermal magnetic behaviour of the complexes indicates the presence of weak antiferromagnetic interactions between Mn3+ or Mn2+ mediated by diamagnetic [Fe(CN)5NO]2− bridges. Irradiation of 1 and 3 with light gives birth to the long-lived metastable states of nitroprusside.