Magnetic behavior and Mössbauer spectra of spin-crossover pyrazolate bridged dinuclear diiron(ii) complexes: X-ray structures of high-spin and low-spin [{Fe(NCBH₃)(py)}₂(μ-bpypz)₂]

Abstract

The synthesis and characterization of new spin-crossover pyrazolato bridged dinuclear [(FeII(NCS)(py))2(mu-bpypz)2] and the corresponding cyanotrihydroborato-kappaN complexes are described together with the X-ray crystal analysis of the latter in both the high-spin and low-spin states as well as the variable temperature magnetic susceptibility and/or Mossbauer spectra demonstrating the spin-crossover which exhibits an one-step process, but not a two-step one characteristic of the known bpym bridged dinuclear complexes.

Mössbauer Investigation of the Photoexcited Spin States and Crystal Structure Analysis of the Spin‐Crossover Dinuclear Complex [{Fe(bt)(NCS)2}2bpym] (bt=2,2′‐Bithiazoline, bpym=2,2′‐Bipyrimidine)

“…Another possible explanation to justify the lack of broken symmetry in the plateau region could be associated with the fact that the HS-LS species are disordered in the crystal, so that the X-ray diffraction analysis only sees the average structure of the HS and LS centres. The structural changes noted between 293 and 30 K in the Fe II coordination environment for 1 are similar to those reported in references [9][10][11].…”

“…The iron atom is in a severely distorted octahedral FeN 6 environment. The thiocyanate FeÀN bond lengths are noticeably shorter than the other four FeÀN distances: FeÀN(6) = 2.042 (13) and FeÀ N(5) = 2.070(14) , compared with Fe À N(1) = 2.112(12), Fe À N(2) = 2.112(12), Fe À N(3) = 2.256 (11) and Fe À N(4) = 2.194 (13) . The average Fe À N bond length of 2.15 (9) indicates that at 293 K compound 1 is in the high-spin state, which is in agreement with magnetic and Mçssbauer data.…”

“…[8] A series of new dinuclear iron(II) SCO systems based on pyrazolate and triazolate bridges reported by Murray, [9] Brooker, [10] Kaizaki [11,12] and co-workers has added new interesting results to this topic. The spin conversion in these complexes takes place by means of the HS-HSQLS-LS transformation.…”

“…At 30 K, the average FeÀN distance is 1.958(4) , showing that the structure is clearly low spin (LS-LS). At 175 K the average Fe À N bond length of 2.052 (11) suggests that there is an intermediate phase. Mçss-bauer investigations of the light-induced excited spin state trapping (LIESST) effect (l = 514 nm, 25 mW cm Keywords: bistability · cooperative effects · dinuclear complexes · iron · photoswitching · spin crossover simultaneously involved, a new wide range of applications and even new fields of research often appear, such as opto-A C H T U N G T R E N N U N G electronics, magnetooptics and spintronics.…”

A Novel Dinuclear FeII Spin‐Crossover Complex Based on a 2,2‐Bipyrimidine Bridge Ligand: [Fe(CH3bipy)(NCS)2]2bpym

“…In this respect, a very gradual SCO behaviour without a plateau has been observed in the {[Fe(dpa)(NCS) 2 ] 2 bpym} derivative, [5] the lack of such a plateau being ascribed to interdimer interactions. Murray [6] and Kaizaki [7] and their groups have reported new dinuclear iron() SCO systems based on pyrazolate bridges in which the conversion takes place through [HSϪHS] …”