Four‐Site Cooperative Spin Crossover in a Mononuclear Fe^II Complex

Abstract

Four-site cooperative spin crossover (SCO) in a mononuclear Fe(II) complex has been observed for the isoselenocyanate complex [(bpte)Fe II (NCSe) 2 ] (bpte = S,S'-bis(2-pyridylmethyl)-1,2-thioethane). The compound has been characterised in four polymorphic crystalline phases. One is SCO-inactive (b phase), one exhibits one-step SCO (g phase) and two exhibit four-site cooperative SCO (a and d phases) as a function of temperature. Crystal structures have been determined over the temperature range 300-100 K for all four polymorphs, and at intervals of 5 K for the most interesting a and d phases. Of the five potentially addressable local spin configurations in a four-site cooperative system, four are observed as ordered crystal structures amongst the polymorphs. The d phase exhibits a remarkable ordered 1HS:3LS structure (HS = high-spin Fe(II), LS = low-spin Fe(II)) below ca 130 K, which establishes conclusively the four-site cooperative nature of the system. The a and d phases are polytypes, but it is difficult to link conclusively the associated two-dimensional structural similarity with the four-site cooperativity. Keywords: spin crossover; polymorphism; magnetism MS27-O4 Synthesis and crystal structure of few new decavanadates. Wieslaw £asocha ab , Vanadates and peroxovanadates are used as valuable catalysts. They can be also applied in medicine thanks to their enzymo-imitative properties. During our studies of new peroxo-vanadates and poli-vanadates we have synthesized three new compounds which belong to the group of deca-vanadates: two organic decavanadates and a rubidium decavanadate. The obtained compounds have the same, island-like type of anion, which is built of VO 6 octahedra. The structure of deca-vanadates can be described on the basis of the structures of b-octamolybdates. If in a-octamolybdate anion, Mo(VI) ions are replaced by V(V) ions V 8 O 26-12 ions will be obtained. When to the V 8 O 26 12 ion two VO 6 octahedra (or VO 3+ after removal of the redundant O atoms) are attached V 10 O 28 6-anion is created. The syntheses were carried out in 30% H 2 O 2. After crystallization, which lasted several days, deca-vanadates without O 2-2 groups were obtained. Explanation of this phenomenon will be the subject of our further research. Lattice parameters and chemical formulas of the obtained compounds: 1. Rb 6 V 10 O 28 .8H 2 O: P2 1 /c, 13.974, 10.595, 34.291 Å, 90, 97.437, 90°, V= 5034.23 Å 3 , Z=6. 2. 5(1-ammoniumpropane)(H 3 O +)V 10 O 28 .H 2 O, P-1, 14.507, 15.502, 15.858Å, 88.22, 81.53, 83.94°, V=3507.21Å 3. Z=3, 3. 2(1,2-diammoniumpropane).2(H 3 O +)V 10 O 28 .4H 2 O, P-1, 8.636, 10.394, 10.959Å, 68.86, 78.92, 66.99°, V= 843.Å 3 .Z=1. Fig. 1. Asymmetric unit of compound 3. Properties and geometry of the synthesized compounds will be compared with the properties and structures of several decavanadates described in a comprehensive survey recently published [1]. The investigated compounds form complex structures often with several molecules in an asymmetric unit. For example, in the structure of the de...

First Cobalt(II) Spin Crossover Compound with N4S2-Donorset

“…The average Fe-N bond length of 1.990 Å and Fe-S bond length of 2.264 Å in C1 (@173 K) are in accordance with those reported in literature and account for an iron(II) ion in the [LS] state [23][24][25][26][27][28][29]. Figure S7 shows the crystal structure/asymmetric unit of C1 (@173 K).…”

Two‐Step Spin Transition in a 1D FeII 1,2,4‐Triazole Chain Compound

“…[25][26][27][28][29] This is illustrated, for example, in the mononuclear Fe II complexes [Fe(2-pic) 3 ]Cl 2 ·EtOH (2-pic = 2-picolylamine) [30] and Fe 4,7,10)],i nw hich 5-NO 2 -sal-N(1,4,7,10)i sahexadentate ligand obtained from the condensation of 5-NO 2 -salicylaldehyde with 1,4,7,10-tetraazadecane. In the case of mononuclear complexes,t he intermediate phase at the plateau region results from symmetry breaking and al ong-or short-range ordering of an intermediate spin state (HS-LS).…”

“…[21] Intriguingly,a ll transitions for this family proceed in one step between the high-spin (HS) and low-spin (LS) states. [25][26][27][28][29][30][31][32][33] The rare examples of 1D chains displayingatwo-step transition present, however,a1:1r atio of LS/HS on the plateau region. [23,24] Over the last decade such two-step events in Fe II and Fe III mononuclear complexes have been shown to be accompanied by as tructural phase transition with crystallographic ordering of HS and LS complexes in the intermediate (INT) phase in various ratios.…”

Synthesis, crystal structures and properties of Ni(NCS)2-4-(hydroxymethyl)pyridine coordination compounds

“…In this case the cations can be linked by pairs of anionic ligands into dimers or chains or can be connected by single anionic ligands into layers [8][9][10][11][12][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46]. Even if for some compounds with terminal N-bonded ligands spin-crossover is observed [5][6][47][48][49][50], the coordination polymers with bridging anionic ligands show a more versatile magnetic behavior [32][33][34][35][36][37][38][39][40].…”