Iron(II) Spin Crossover (SCO) Materials Based on Dipyridyl-N-Alkylamine

We present here a new series of spin crossover (SCO) Fe(II) complexes based on dipyridyl-N-alkylamine and thiocyanate ligands, with the chemical formulae [Fe(dpea)2(NCS)2] (1) (dpea = 2,2’-dipyridyl-N-ethylamine), I-[Fe(dppa)2(NCS)2], (2) II-[Fe(dppa)2(NCS)2], and (2’) (dppa = 2,2’-dipyridyl-N-propylamine). The three complexes displayed nearly identical discrete molecular structures, where two chelating ligands (dpea (1) and dppa (2 and 2’)) stand in the cis-positions, and two thiocyanato-κN ligands complete the coordination sphere in the two remaining cis-positions. Magnetic studies as a function of temperature revealed the presence of a complete high-spin (HS) to low-spin (LS) transition at T1/2 = 229 K for 1, while the two polymorphs I-[Fe(dppa)2(NCS)2] (2) and II-[Fe(dppa)2(NCS)2] (2’) displayed similar magnetic behaviors with lower transition temperatures (T1/2 = 211 K for 2; 212 K for 2’). Intermolecular contacts in the three complexes indicated the absence of any significant interaction, in agreement with the gradual SCO behaviors revealed by the magnetic data. The higher transition temperature observed for complex 1 agrees well with the more pronounced linearity of the Fe–N–C angles recently evidenced by experimental and theoretical magnetostructural studies.

Download Full-text

Steric Trapping of the High Spin State in FeIII Quinolylsalicylaldimine Complexes

Australian Journal of Chemistry ◽

10.1071/ch14177 ◽

2014 ◽

Vol 67 (11) ◽

pp. 1574 ◽

Cited By ~ 4

Author(s):

Darunee Sertphon ◽

David J. Harding ◽

Phimphaka Harding ◽

Keith S. Murray ◽

Boujemaa Moubaraki ◽

...

Keyword(s):

Schiff Base ◽

Electronic Properties ◽

High Spin ◽

Spin State ◽

Schiff Base Ligand ◽

Room Temperature ◽

Spin Crossover ◽

High Spin State ◽

Electrochemical Studies ◽

Magnetic Studies

A new sterically bulky Schiff base ligand, N-(8-quinolyl)-5-tert-butylsalicylaldimine (Hqsal-5-tBu) has been prepared and a series of FeIII complexes, [Fe(qsal-5-tBu)2]Y (Y = Cl 1, ClO4 2, NO3 3, BF4 4) utilising this ligand are reported and fully characterised. UV-vis spectroscopic and electrochemical studies indicate that 1–4 are high spin (HS) in solution at room temperature and further suggest that the tBu group only slightly alters the electronic properties of 1–4 compared with related [Fe(qsal-5-X)2]+ systems. The structures of [Fe(qsal-5-tBu)2]Cl·4MeOH·H2O 1, [Fe(qsal-5-tBu)2]ClO4·MeOH 2, and [Fe(qsal-5-tBu)2]NO3 3 determined at 100 K reveal HS FeIII centres in all cases. Four-fold parallel aryl embraces and π–π interactions serve to link the cations forming 2D sheets mirroring the motifs found in other [Fe(qsal-5-X)2]+ complexes. Despite this the tBu group causes strong distortions at the Fe centre which as magnetic studies reveal prevent spin crossover trapping 1–4 in the HS state.

Download Full-text

Unusual High Thermal Stablility of a 2D → 3D Polycatenated Fe(II) Metal–Organic Framework Showing Guest-Dependent Spin-Crossover Behavior and High Spin-Transition Temperature

Crystal Growth & Design ◽

10.1021/cg3007876 ◽

2012 ◽

Vol 12 (8) ◽

pp. 3845-3848 ◽

Cited By ~ 58

Author(s):

Xiu-Tang Zhang ◽

Di Sun ◽

Bao Li ◽

Li-Ming Fan ◽

Bin Li ◽

...

Keyword(s):

Transition Temperature ◽

High Spin ◽

Spin Crossover ◽

Metal Organic Framework ◽

Spin Transition ◽

Crossover Behavior ◽

Metal Organic ◽

Organic Framework

Download Full-text

Magnetic Properties of Fe(II) Complexes of Cyclam Derivative with One p-Aminobenzyl Pendant Arm

Metals ◽

10.3390/met10030366 ◽

2020 ◽

Vol 10 (3) ◽

pp. 366

Author(s):

Bohuslav Drahoš ◽

Peter Antal ◽

Ivan Šalitroš ◽

Radovan Herchel

Keyword(s):

Crystal Structure ◽

Magnetic Properties ◽

High Spin ◽

Spin Crossover ◽

Crystal Packing ◽

Theoretical Calculations ◽

High Spin State ◽

Magnetic Data ◽

Pendant Arm ◽

Pendant Arms

In order to prepare an Fe(II) spin crossover (SCO) complex that could be consequently modified to a bimetallic coordination compound that possesses another magnetic property of interest, a specially designed ligand L-NH2 (1-(4-aminobenzyl)-4,11-bis(pyridine-2-ylmethyl)- 1,4,8,11-tetraazacyclotetradecane) was prepared. This ligand consists of a macrocyclic cyclam part containing two 2-pyridylmethyl pendant arms (expecting SCO upon Fe(II) complexation) and one p-aminobenzyl pendant arm with an NH2 group. The presence of this group enables the consequent transformation to various functional groups for the selective complexation of other transition metals or lanthanides (providing the second property of interest). Furthermore, the performed theoretical calculations (TPSSh/def2-TZVP) predicted SCO behavior for the Fe(II) complex of L-NH2. Thus, Fe(II) complexes [Fe(L-NH2)](ClO4)2 (1) and [Fe(L-NH2)]Cl2·6H2O (2) were synthesized and thoroughly characterized. Based on the crystal structure of an isostructural analogous Ni(II) complex [Ni(L-NH2)]Cl2·6H2O (3), the coordination number six was confirmed with an octahedral coordination sphere and a cis-arrangement of the pyridine pendant arms. The measured magnetic data confirmed the high-spin behavior of both compounds with large magnetic anisotropy (D = 17.8 for 1 and 20.9 cm−1 for 2 complemented in both cases also with large rhombicity), though unfortunately without any indication of the SCO behavior with decreasing temperature. The lack of SCO can be ascribed to the crystal packing and/or the non-covalent intermolecular interactions stabilizing the high-spin state in the solid state.

Download Full-text

Anion Influence on Spin State in Two Novel Fe(III) Compounds: [Fe(5F-sal2333)]X

Crystals ◽

10.3390/cryst9010019 ◽

2018 ◽

Vol 9 (1) ◽

pp. 19 ◽

Cited By ~ 5

Author(s):

Sriram Sundaresan ◽

Irina Kühne ◽

Conor Kelly ◽

Andrew Barker ◽

Daniel Salley ◽

...

Keyword(s):

High Spin ◽

Spin State ◽

Spin Crossover ◽

Structural Investigation ◽

Variable Temperature ◽

Magnetic Data ◽

Crystallographic Site ◽

Hydrogen Atoms ◽

High Spin Complex ◽

Spin Complex

Structural and magnetic data on two iron (III) complexes with a hexadentate Schiff base chelating ligand and Cl− or BPh4− counterions are reported. In the solid state, the Cl− complex [Fe(5F-sal2333)]Cl, 1, is high spin between 5–300 K while the BPh4− analogue [Fe(5F-sal2333)]BPh4, 2, is low spin between 5–250 K, with onset of a gradual and incomplete spin crossover on warming to room temperature. Structural investigation reveals different orientations of the hydrogen atoms on the secondary amine donors in the two salts of the [Fe(5F-sal2333)]+ cation: high spin complex [Fe(5F-sal2333)]Cl, 1, crystallizes with non-meso orientations while the spin crossover complex [Fe(5F-sal2333)]BPh4, 2, crystallizes with a combination of meso and non-meso orientations disordered over one crystallographic site. Variable temperature electronic absorption spectroscopy of methanolic solutions of 1 and 2 suggests that both are capable of spin state switching in the solution.

Download Full-text

Abrupt spin crossover in iron(iii) complexes with aromatic anions

Dalton Transactions ◽

10.1039/c9dt02373a ◽

2019 ◽

Vol 48 (41) ◽

pp. 15515-15520 ◽

Cited By ~ 5

Author(s):

Sharon E. Lazaro ◽

Adil Alkaş ◽

Seok J. Lee ◽

Shane G. Telfer ◽

Keith S. Murray ◽

...

Keyword(s):

Transition Temperature ◽

Spin Crossover ◽

Spin Transition ◽

Halogen Bonds ◽

Aromatic Anions

Two iron(iii) complexes, [Fe(qsal-X)2]OTs·nH2O, are found to exhibit abrupt spin crossover with the spin transition temperature substituent dependent, and X⋯O halogen bonds linking the spin centres.

Download Full-text

Spin Balls and Spin Barbells. Preparation and Magnetic Studies of S = 7/2 Dendritic Heptaradical and Progress Toward Very High Spin Dendrimers1

Molecular Crystals and Liquid Crystals Science and Technology Section A Molecular Crystals and Liquid Crystals ◽

10.1080/10587259308035720 ◽

1993 ◽

Vol 232 (1) ◽

pp. 305-312 ◽

Cited By ~ 5

Author(s):

Andrzej Rajca ◽

Suchada Utamapanya

Keyword(s):

High Spin ◽

Magnetic Studies ◽

Very High

Download Full-text

The Flexibility of Long Chain Substituents Influences Spin-Crossover in Isomorphous Lipid Bilayer Crystals

Chemical Communications ◽

10.1039/d1cc01073e ◽

2021 ◽

Author(s):

Iurii Galadzhun ◽

Rafal Kulmaczewski ◽

Namrah Shahid ◽

Oscar Cespedes ◽

Mark J Howard ◽

...

Keyword(s):

Lipid Bilayer ◽

High Spin ◽

Room Temperature ◽

Spin Crossover ◽

Pyridine Derivatives ◽

Long Chain

[Fe(bpp)2][BF4]2 (bpp = 2,6-di{pyrazol-1-yl}pyridine) derivatives bearing a bent geometry of hexadec-1-ynyl or hexadecyl substituents pyrazole are isomorphous, and high-spin at room temperature. However, only the latter compound undergoes an abrupt,...

Download Full-text

Solvent-Induced Hysteresis Loop in Anionic Spin Crossover (SCO) Isomorph Complexes

Magnetochemistry ◽

10.3390/magnetochemistry7060075 ◽

2021 ◽

Vol 7 (6) ◽

pp. 75

Author(s):

Emmelyne Cuza ◽

Samia Benmansour ◽

Nathalie Cosquer ◽

Françoise Conan ◽

Carlos J. Gómez-García ◽

...

Keyword(s):

Metal Ion ◽

Spin Crossover ◽

Magnetic Behaviour ◽

Magnetic Studies ◽

Tridentate Ligands ◽

Tripodal Ligand ◽

Single Crystal Structures ◽

One Step ◽

Lower Temperature ◽

Step Transition

Reaction of Fe(II) with the tris-(pyridin-2-yl)ethoxymethane (py3C-OEt) tripodal ligand in the presence of the pseudohalide ancillary NCSe- (E = S, Se, BH3) ligand leads to the mononuclear complex [Fe(py3C-OEt)2][Fe(py3C-OEt)(NCSe)3]2·2CH3CN (3), which has been characterised as an isomorph of the two previously reported complexes, Fe(py3C-OEt)2][Fe(py3C-OEt)(NCE)3]2·2CH3CN, with E = S (1), BH3 (2). X-ray powder diffraction of the three complexes (1–3), associated with the previously reported single crystal structures of 1–2, revealed a monomeric isomorph structure for 3, formed by the spin crossover (SCO) anionic [Fe(py3C-OEt)(NCSe)3]− complex, associated with the low spin (LS) [Fe(py3C-OEt)2]2+ cationic complex and two solvent acetonitrile molecules. In the [Fe(py3C-OEt)2]2+ complex, the metal ion environment involves two py3C-OEt tridentate ligands, while the [Fe(py3C-OEt)(NCSe)3]− anion displays a hexacoordinated environment involving three N-donor atoms of one py3C-OEt ligand and three nitrogen atoms arising from the three (NCSe)− coligands. The magnetic studies for 3 performed in the temperature range 300-5-400 K, indicated the presence of a two-step SCO transition centred around 170 and 298 K, while when the sample was heated at 400 K until its complete desolvation, the magnetic behaviour of the high temperature transition (T1/2 = 298 K) shifted to a lower temperature until the two-step behaviour merged with a gradual one-step transition at ca. 216 K.

Download Full-text

Donor Atom Preference of Organoruthenium and Organorhodium Cations on the Interaction with Novel Ambidentate (N,N) and (O,O) Chelating Ligands in Aqueous Solution

Molecules ◽

10.3390/molecules26123586 ◽

2021 ◽

Vol 26 (12) ◽

pp. 3586

Author(s):

Sándor Nagy ◽

András Ozsváth ◽

Attila Cs. Bényei ◽

Etelka Farkas ◽

Péter Buglyó

Keyword(s):

Aqueous Solution ◽

Metal Ion ◽

Platinum Group Metal ◽

Molecular Structures ◽

Chelating Ligands ◽

Metal Ion Binding ◽

Biologically Relevant ◽

X Ray Crystallography ◽

Ligand Ratio ◽

Ph Range

Two novel, pyridinone-based chelating ligands containing separated (O,O) and (Namino,Nhet) chelating sets (Namino = secondary amine; Nhet = pyrrole N for H(L3) (1-(3-(((1H-pyrrole-2-yl)methyl)amino)propyl)-3-hydroxy-2-methylpyridin-4(1H)-one) or pyridine N for H(L5) (3-hydroxy-2-methyl-1-(3-((pyridin-2-ylmethyl)amino)propyl)pyridin-4(1H)-one)) were synthesized via reduction of the appropriate imines. Their proton dissociation processes were explored, and the molecular structures of two synthons were assessed by X-ray crystallography. These ambidentate chelating ligands are intended to develop Co(III)/PGM (PGM = platinum group metal) heterobimetallic multitargeted complexes with anticancer potential. To explore their metal ion binding ability, the interaction with Pd(II), [(η6-p-cym)Ru]2+ and [(η5-Cp*)Rh]2+ (p-cym = 1-methyl-4-isopropylbenzene, Cp* = pentamethyl-cyclopentadienyl anion) cations was studied in aqueous solution with the combined use of pH-potentiometry, NMR and HR ESI-MS. In general, organorhodium was found to form more labile complexes over ruthenium, while complexation of the (N,N) chelating set was slower than the processes of the pyridinone unit with (O,O) coordination. Formation of the organoruthenium complexes starts at lower pH (higher thermodynamic stabilities of the corresponding complexes) than for [(η5-Cp*)Rh]2+ but, due to the higher affinity of [η6-p-cym)Ru]2+ towards hydrolysis, the complexed ligands are capable of competing with hydroxide ion in a lesser extent than for the rhodium systems. As a result, under biologically relevant conditions, the rhodium binding effectivity of the ligands becomes comparable or even slightly higher than their effectivity towards ruthenium. Our results indicate that H(L3) is a less efficient (N,N) chelator for these metal ions than H(L5). Similarly, due to the relative effectivity of the (O,O) and (N,N) chelates at a 1:1 metal-ion-to-ligand ratio, H(L5) coordinates in a (N,N) manner to both cations in the whole pH range studied while, for H(L3), the complexation starts with (O,O) coordination. At a 2:1 metal-ion-to-ligand ratio, H(L3) cannot hinder the intensive hydrolysis of the second metal ion, although a small amount of 2:1 complex with [(η5-Cp*)Rh]2+ can also be detected.

Download Full-text