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

Abstract

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 [Mn^II(dapsc)]²⁺ and anionic [Fe^II(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.