Incomplete Spin Crossover Research Articles

Guest Induced Strong Cooperative One- and Two-Step Spin Transitions in Highly Porous Iron(II) Hofmann-Type Metal-Organic Frameworks.

The synthesis, crystal structure, magnetic, calorimetric, and Mössbauer studies of a series of new Hofmann-type spin crossover (SCO) metal-organic frameworks (MOFs) is reported. The new SCO-MOFs arise from self-assembly of FeII, bis(4-pyridyl)butadiyne (bpb), and [Ag(CN)2]- or [MII(CN)4]2- (MII = Ni, Pd). Interpenetration of four identical 3D networks with α-Po topology are obtained for {Fe(bpb)[AgI(CN)2]2} due to the length of the rod-like bismonodentate bpb and [Ag(CN)2]- ligands. The four networks are tightly packed and organized in two subsets orthogonally interpenetrated, while the networks in each subset display parallel interpenetration. This nonporous material undergoes a very incomplete SCO, which is rationalized from its intricate structure. In contrast, the single network Hofmann-type MOFs {Fe(bpb)[MII(CN)4]}·nGuest (MII = Ni, Pd) feature enhanced porosity and display complete one-step or two-step cooperative SCO behaviors when the pores are filled with two molecules of nitrobenzene or naphthalene that interact strongly with the pyridyl and cyano moieties of the bpb ligands via π-π stacking. The lack of these guest molecules favors stabilization of the high-spin state in the whole range of temperatures. However, application of hydrostatic pressure induces one- and two-step SCO.

A Family of Octahedral Magnetic Molecules Based on [NbIV(CN)8]4.

A building block approach has been used to prepare a new family of hexanuclear magnetic molecules Mn4Nb2, Fe4Nb2, and Co4Nb2 of general formula {[MII(tmphen)2]4[NbIV(CN)8]2}·solv (M = Mn, Fe, Co; tmphen = 3,4,7,8-tetramethyl-1,10-phenanthroline; solv = MeOH and/or H2O). Mn4Nb2 exhibits a magnetocaloric effect at temperatures close to 1.8 K, and Fe4Nb2 undergoes an incomplete gradual spin crossover and a photomagnetic response related to light-induced excited spin state trapping.

Nonanuclear Spin-Crossover Complex Containing Iron(II) and Iron(III) Based on a 2,6-Bis(pyrazol-1-yl)pyridine Ligand Functionalized with a Carboxylate Group.

The synthesis and magnetostructural characterization of [Fe(III)3(μ3-O)(H2O)3[Fe(II)(bppCOOH)(bppCOO)]6](ClO4)13·(CH3)2CO)6·(solvate) (2) are reported. This compound is obtained as a secondary product during synthesis of the mononuclear complex [Fe(II)(bppCOOH)2](ClO4)2 (1). The single-crystal X-ray diffraction structure of 2 shows that it contains the nonanuclear cluster of the formula [Fe(III)3(μ3-O)(H2O)3[Fe(II)(bppCOOH)(bppCOO)]6](13+), which is formed by a central Fe(III)3O core coordinated to six partially deprotonated [Fe(II)(bppCOOH)(bppCOO)](+) complexes. Raman spectroscopy studies on single crystals of 1 and 2 have been performed to elucidate the spin and oxidation states of iron in 2. These studies and magnetic characterization indicate that most of the iron(II) complexes of 2 remain in the low-spin (LS) state and present a gradual and incomplete spin crossover above 300 K. On the other hand, the Fe(III) trimer shows the expected antiferromagnetic behavior. From the structural point of view, 2 represents the first example in which bppCOO(-) acts as a bridging ligand, thus forming a polynuclear magnetic complex.

A Family of Dinuclear Iron(II) SCO Compounds Based on a 1,3,4‐Thiadiazole Bridging Ligand

A new family of dinuclear iron(II) spin-crossover (SCO) compounds with the formula [Fe2(μ-L)2]X4, with three different counteranions [X = BF4– (1), ClO4– (2) and F3CSO3– (3)], was prepared and characterized by single-crystal X-ray diffraction, variable-temperature magnetic susceptibility and Mossbauer measurements. These are the first dinuclear iron(II) SCO complexes with a 1,3,4-thiadiazole bridging ligand L {with L = 2,5-bis[(2-pyridylmethyl)amino]methyl-1,3,4-thiadiazole}. The magnetic measurements reveal a gradual and incomplete SCO of the three compounds around room temperature, starting from a diamagnetic [LS–LS] state. The diamagnetic ground state is in agreement with the single-crystal X-ray diffraction and Mossbauer data.

Synthesis and magnetic properties of iron(II) closo-borate complexes with tris(3,5-dimethylpyrazol-1-yl)methane

Methods are developed for preparing iron(II) complexes with tris(3,5-dimethylpyrazol-1-yl)methane {HC(3,5-dmpz)3} and closo-borate(2-) ions, namely [Fe{HC(3,5-dmpz)3}2]B10H10 · H2O (I) and [Fe{HC(3,5-dmpz)3}2]B12H12 · H2O (II). These complexes were characterized by static magnetic susceptibility measurements (2–325 K), electronic spectroscopy (diffuse reflectance spectra), and IR spectroscopy. The complexes have a distorted octahedral geometry of the coordination polyhedron; the coordination core is FeN6. μeff(T) studies show low-temperature incomplete spin crossover in complex I and antiferromagnetic exchange coupling among iron(II) unpaired electrons at temperatures below 90 K in complex II. Complex I shows thermochromism; the color transition upon cooling is white ↔ pink.

A Family of Dinuclear Iron(II) SCO Compounds Based on a 1,3,4‐Thiadiazole Bridging Ligand

AbstractA new family of dinuclear iron(II) spin‐crossover (SCO) compounds with the formula [Fe2(μ‐L)2]X4, with three different counteranions [X = BF4– (1), ClO4– (2) and F3CSO3– (3)], was prepared and characterized by single‐crystal X‐ray diffraction, variable‐temperature magnetic susceptibility and Mössbauer measurements. These are the first dinuclear iron(II) SCO complexes with a 1,3,4‐thiadiazole bridging ligand L {with L = 2,5‐bis[(2‐pyridylmethyl)amino]methyl‐1,3,4‐thiadiazole}. The magnetic measurements reveal a gradual and incomplete SCO of the three compounds around room temperature, starting from a diamagnetic [LS–LS] state. The diamagnetic ground state is in agreement with the single‐crystal X‐ray diffraction and Mössbauer data.

Syntheses, hydrogen-bonded assembly structures, and spin crossover properties of [FeIII(Him)2(n-MeOhapen)]PF6 (Him = imidazole and n-MeOhapen = N,N′-bis(n-methoxy-2-oxyacetophenylidene)ethylenediamine); n = 4, 5, 6)

Three iron(III) complexes, [FeIII(Him)2(n-MeOhapen)]PF6 (1: n=4, 2: n=5, 3: n=6), where Him=imidazole and n-MeOhapen=N,N′-bis(n-methoxy-2-oxyacetophenylidene)ethylenediamine, were synthesized. Each FeIII ion was coordinated by N4O2 donor atoms of equatorial n-MeOhapen and two axial Him. The saturated FeC2N2 chelate ring involving the ethylenediamine moiety adopted a gauche conformation and the two phenylidene planes of [FeIII(Him)2(n-MeOhapen)]+ were oriented opposite to the FeO2N2 coordination plane. Two adjacent [FeIII(Him)2(4-MeOhapen)]+ cations in 1 were connected via PF6− ions by hydrogen bonds between the imidazole group and PF6− to give a one-dimensional chain. Two adjacent cations in 2 were connected via hydrogen bonds between the phenylidene oxygen and imidazole atoms to form a cyclic dimer structure. Two EtOH molecules were involved in a hydrogen-bonded cyclic dimer structure in 3. Compounds 1 and 2 showed spin crossover behavior, but 3 showed incomplete spin crossover.

Structural Chemistry of Tetracyanopyrrolide (Part 2): Spin Crossover in a Bis‐Tripodal Iron(II) Complex

AbstractThe mononuclear iron(II) complex [Fe(tpm)2]2+(tcp–)2 (1) containing the neutral tripodal N3‐donor ligand tris(pyrazol‐1‐yl)methane (tpm) and the mononegative tetracyanopyrrolide (tcp) as counter‐anion was characterized by X‐ray diffraction on twinned crystals and investigated in the solid state by magnetic susceptibility measurements and differential scanning calorimetry. Structural investigations at 123 K reveal Fe–N distances typical for low‐spin d6 iron(II). Compound 1 undergoes a gradual, incomplete spin crossover in the examined temperature range 1.9–400 K. Comparisons are made with known analogous [Fe(tpm)2]2+(X–)2 compounds bearing different anions X, which display similar crossover behavior.

Electronic effects of ligand substitution on spin crossover in a series of diiminoquinonoid-bridged Fe(II)2 complexes.

A series of four isostructural Fe(II)2 complexes, [(TPyA)2Fe2((X)L)](2+) (TPyA = tris(2-pyridylmethyl)amine; (X)L(2-) = doubly deprotonated form of 3,6-disubstituted-2,5-dianilino-1,4-benzoquinone; X = H, Br, Cl, and F), were synthesized to enable a systematic study of electronic effects on spin crossover behavior. Comparison of X-ray diffraction data for these complexes reveals the sole presence of high-spin Fe(II) at 225 K and mixtures of high-spin and low-spin Fe(II) at 100 K, which is indicative of incomplete spin crossover. In addition, crystal packing diagrams show that these complexes are well-isolated from one another in the solid state, owing primarily to the presence of bulky tetra(aryl)borate counteranions, such that spin crossover is likely not significantly affected by intermolecular interactions. Variable-temperature dc magnetic susceptibility data confirm the structural observations and reveal that 54(1), 56(1), 62(1), and 84(1)% of Fe(II) centers remain high-spin even below 65 K. Moreover, fits to magnetic data provide crossover temperatures of T1/2 = 160(1), 124(1), 121(1), and 110(1) K for X = H, Br, Cl, and F, respectively, along with enthalpies of ΔH = 11.4(3), 8.5(3), 8.3(3), and 7.5(2) kJ/mol, respectively. These parameters decrease with increasing electronegativity of X and thus increasing electron-withdrawing character of (X)L(2-), suggesting that the observed trends originate primarily from inductive effects of X. Moreover, when plotted as a function of the Pauling electronegativity of X, both T1/2 and ΔH undergo a linear decrease. Further analyses of the low-temperature magnetic data and variable-temperature Mössbauer spectroscopy suggest that the incomplete spin crossover behavior in [(TPyA)2Fe2((X)L)](2+) is best described as a transition from purely [FeHS-FeHS] (HS = high-spin) complexes at high temperature to a mixture of [FeHS-FeHS] and [FeHS-FeLS] (LS = low-spin) complexes at low temperature, with the number of [FeHS-FeHS] species increasing with decreasing electron-withdrawing character of (X)L(2-).

Iron(III) complexes with pentadentate Schiff-base ligands: Influence of crystal packing change and pseudohalido coligand variations on spin crossover

Two novel iron(III) complexes involving pentadentate Schiff-base ligands, [Fe(LBr)(L1)], show temperature induced incomplete spin crossover of a gradual nature. While for the L1=NCSe− coligand the transition temperature (326K or 317K) lies above room temperature, the N3− coligand causes its drop down to 143K or 140K (two values were obtained by different models). This shift is associated with a significant decrease of the enthalpy of the transition from about ΔH=6.1kJmol−1 to ca. ΔH=1.7kJmol−1, while the entropy of the transition is about ΔS=19JK−1mol−1 and ΔS=12JK−1mol−1, respectively. Two analogous complexes with Cl− and NCS− coligands remain high-spin over the whole temperature range.

Control of the spin state by charge and ligand substitution: two-step spin crossover behaviour in a novel neutral iron(II) complex.

The influence of the charge and steric hindrance on the spin state of a series of four monomeric Fe(II) complexes derived from the tridentate ligands 2-(1H-benzoimidazol-2-yl)-1,10-phenanthroline (Hphenbi) and 2-(1H-benzoimidazol-2-yl)-9-methyl-1,10-phenanthroline (Hmphenbi) and their deprotonated forms (phenbi(-), mphenbi(-)) are investigated. The crystal structure and magnetic properties show that [Fe(Hphenbi)2](BF4)2·1.5C6H5NO2·H2O (1) and its neutral form [Fe(phenbi)2](0)·2CHCl3·H2O (2) are low-spin complexes at 400 K due to the strong ligand field imparted by the terpyridine-like ligand. In contrast, the steric hindrance induced by the methyl group in [Fe(Hmphenbi)2](BF4)2 (3) stabilizes the high-spin state of the Fe(II) ion at all temperatures. Application of a hydrostatic pressure of 0.43 GPa shows that3 displays incomplete thermal-induced spin crossover behaviour. However, upon deprotonation of the ligand the resulting neutral complex [Fe(mphenbi)2]·2CHCl3 (4) shows a complete two-step spin crossover behaviour at ambient pressure.

An investigation of photo- and pressure-induced effects in a pair of isostructural two-dimensional spin-crossover framework materials.

Two new isostructural iron(II) spin-crossover (SCO) framework (SCOF) materials of the type [Fe(dpms)2(NCX)2] (dpms = 4,4'-dipyridylmethyl sulfide; X = S (SCOF-6(S)), X = Se (SCOF-6(Se))) have been synthesized. The 2D framework materials consist of undulating and interpenetrated rhomboid (4,4) nets. SCOF-6(S) displays an incomplete SCO transition with only approximately 30 % conversion of high-spin (HS) to low-spin iron(II) sites over the temperature range 300-4 K (T1/2 = 75 K). In contrast, the NCSe(-) analogue, SCOF-6(Se), displays a complete SCO transition (T1/2 = 135 K). Photomagnetic characterizations reveal quantitative light- induced excited spin-state trapping (LIESST) of metastable HS iron(II) sites at 10 K. The temperature at which the photoinduced stored information is erased is 58 and 50 K for SCOF-6(S) and SCOF-6(Se), respectively. Variable-pressure magnetic measurements were performed on SCOF-6(S), revealing that with increasing pressure both the T1/2 value and the extent of spin conversion are increased; with pressures exceeding 5.2 kbar a complete thermal transition is achieved. This study confirms that kinetic trapping effects are responsible for hindering a complete thermally induced spin transition in SCOF-6(S) at ambient pressure due to an interplay between close T1/2 and T(LIESST) values.

Solution and solid state properties of Fe(III) complexes bearing N-ethyl-N-(2-aminoethyl)salicylaldiminate ligands

The effect of the phenolate ring derivatisation on the magnetic properties of Fe(III) complexes bearing N-ethyl-N-(2-aminoethyl)salicylaldiminate ligands both in solid state and solution have been investigated. Two new complexes [Fe(3,5-Br-salEen)2]ClO4.EtOH (5) and [Fe(3,5-Br-salEen)2]BPh4.DMF (6) have been synthesised. SQUID magnetometry studies on these complexes showed that while complex 5 is in the low-spin (LS) state, complex 6 displays a gradual and incomplete spin crossover (SCO) transition over the temperature measured. Solution measurements on a series of six complexes – [Fe(salEen)2]ClO4 (1), [Fe(salEen)2]BPh4·0.5H2O (2), [Fe(5-Br-salEen)2]ClO4 (3), [Fe(5-Br-salEen)2]BPh4·DMF (4), [Fe(3,5-Br-salEen)2]ClO4·EtOH (5) and [Fe(3,5-Br-salEen)2]BPh4·DMF (6) – were performed by UV–vis and NMR spectroscopies and cyclic voltammetry. Solution studies show that the presence of electron withdrawing groups (bromine atoms) affect the electronic density at the phenolate ring, thus influencing the ligand field strength and the separation between the t2g and eg* energy levels. The presence of two bromide substituents at the phenolate ring has a more pronounced effect on the magnetic behaviour in solution than in the solid state, with both complexes 5 and 6 adopting preferentially the LS state. Electrochemical studies of complexes 1–6 reveal that the reduction of the metallic centres in the complexes with electron withdrawing groups is easier, with E1/2 values of iron moving to more positive potentials with the number of bromide substituents at the phenolate ring.

Iron(II) closo-borate complexes with 1,2,4-triazole derivatives: Spin crossover in the iron(II) closo-borate complexes with tris(pyrazol-1-yl)methane

Methods of synthesis of iron(II) complexes containing cluster closo-borate anions—[Fe(Htrz)3]B10Cl10 (I) (HTrz is 1,2,4-triazole), [Fe(NH2Trz)3]B10Cl10 · 2H2O (II) (NH2Trz is 4-amino-1,2,4-triazole), [Fe{HC(pz)3}2]B10Cl10 (III), [Fe{HC(pz)3}2]B10H10 (IV), and [Fe{HC(pz)3}2]B12H12 · 2H2O (V) (HC(pz)3 is tris(pyrazol-1-yl)methane)—have been developed. The compounds have been studied by the static magnetic susceptibility method (78–500 K) and electronic, IR, and EXAFS spectroscopy. Complexes I and II in the temperature range under consideration remain in the high-spin state. Low-spin complex III shows incomplete spin crossover and decomposes on heating above 440 K. Complexes IV and V are characterized by reversible spin crossover 1 A 1 ⇔ 5 T 2 accompanied by thermochromism (the pink ⇔ white color change). The crossover temperature (T c) for IV and V is 375 and 405 K, respectively.

Reprint of “Facial and meridional geometrical isomers of tris(2-methylimidazol-4-yl-methylideneaminobenzyl)iron(II) with Δ- and Λ-configurations and their enantio-discriminative assembly via imidazole⋯chloride hydrogen bonding and spin cross-over properties”

A bidentate 2-methylimidazol-4-yl-methylideneaminobenzyl ligand (HLMe-Benz) reacts with FeIICl2·4H2O and NaPF6 at a 3:1:1 molar ratio to yield a tris(2-methylimidazol-4-yl-methylideneaminobenzyl)iron(II) chloride hexafluorophosphate solvate with the formula of [FeII(HLMe-Benz)3]Cl·PF6·solvent. Meridional and facial geometrical isomers, i.e., mer-[FeII (HLMe-Benz)3]Cl·PF6·1.5H2O (1·PF6·1.5H2O) and fac-[FeII(HLMe-Benz)3]Cl·PF6·EtOH·H2O (2·PF6·EtOH·H2O), were selectively crystallized from methanol and ethanol solutions, respectively. fac-[FeII(HLMe-Benz)3]Cl·SbF6·H2O (2·SbF6·H2O) and fac-[FeII(HLMe-Benz)3]Cl·ClO4·EtOH·H2O (2·ClO4·EtOH·H2O) are synthesized in ethanol, using the corresponding anions. Each FeII ion has an octahedral coordination geometry with N6 donor atoms from three bidentate ligands. All three imidazole groups in both the fac- and mer-[FeII(HLMe-Benz)3]2+ cations are hydrogen-bonded to neighboring three Cl− ions, and each Cl− ion is hydrogen-bonded to three imidazole groups of three neighboring complex cations; this results in the formation of hydrogen-bonded assembly structures. mer-Complex 1·PF6·1.5H2O forms a heterochiral two-dimensional (2D) network structure comprised of cyclic {mer-[FeII(HLMe-Benz)3]2+⋯Cl−}3 units with an ΔΔΛ or ΛΛΔ configuration; the PF6− ions occupy the spaces between the 2D layers. All the fac-complexes have isomorphous cubane-like tetrameric structures, i.e., {fac-[FeII(HLMe-Benz)3]2+⋯Cl−}4. The tetranuclear structure comprises four homo-chiral fac-Δ- or fac-Λ-[FeII(HLMe-Benz)3]2+ cations and four Cl− ions interconnected by twelve imidazole-chloride hydrogen bonds to form a chiral cubane supramolecule that encapsulates one counter anion. In the crystal lattice, the cubane-like tetramers with opposite chiralities are alternately arrayed. The temperature dependence of the magnetic susceptibilities and Mössbauer spectra reveal that the fac-complexes show incomplete spin crossover behavior, while the mer-complex shows a gradual spin crossover between high-spin (HS, S=2) and low-spin (LS, S=0) states.

Two Mononuclear Iron(II) Spin‐Crossover Complexes with a N4O2 Coordination Sphere

AbstractTwo mononuclear spin‐crossover compounds Fe(L1)2 (1) and Fe(L2)2 (2) {HL1 = 2‐hydroxy‐3‐methyl‐N′‐[1‐(pyridine‐2‐yl)butylidene]benzohydrazide, HL2 = 2‐hydroxy‐N′‐[1‐(pyridine‐2‐yl)butylidene]benzohydrazide} were successfully synthesized. The magnetic measurements of the compounds revealed different thermal magnetic behavior. Compound 1 undergoes a gradual complete thermal spin crossover (SCO) with T1/2↑/↓ = 243/240 K and a hysteresis loop of 3 K. Compound 2 shows a gradual incomplete SCO during the measurable temperature region with T1/2 ≈ 330 K. Through the comparison of the magnetic and structural results for 1 and 2 with previously reported related compounds, the alkyl substitutions of the ligand were considered to affect the ligand‐field strength and hydrogen‐bonding interactions. In addition, photomagnetism results showed an 87 % photoconversion and 36 K of T(LIESST) (LIESST = light‐induced excited spin‐state trapping) for compound 1. The results enrich the knowledge on how to control the spin‐crossover behavior in the new system.

2D iron(II) spin crossover complex with 3,5-lutidine

2D coordination polymer iron(II) spin crossover complexes containing 3,5-lutidine with host framework Fe(3,5-lutidine)2Ni(CN)4were synthesized. Their spin crossover properties were studied by temperature dependent 57Fe Mossbauer spectroscopy. Materials show gradual incomplete spin crossover with distinct thermochromism, while only 25 % of iron(II) ions are switched to the low spin state at 80 K, as determined by a detailed 57Fe Mossbauer study.

Supramolecular modulation of spin crossover profile in manganese(III)

Six salts of mononuclear manganese(III) complexes with Schiff-base ligands L3–L5 are reported. Solvated complexes with L3, [MnL3]ClO4·0.5MeOH, 3a, and [MnL3]NO3·EtOH, 3b, are low spin (LS) at 80 K and exhibit a gradual and incomplete spin crossover (SCO) on warming to 281 K. Complexes with L4, [MnL4]ClO4, 4a, and [MnL4]NO3, 4b, are predominantly high spin (HS) at RT and undergo gradual and incomplete SCO on cooling. Complexes [MnL5]NO3, 5b, and [MnL5]PF6, 5c, are fully HS over the measured temperature range. Both salts with the dihalogenated ligand L3, 3a and 3b, crystallise with alcohol solvent molecules and exhibit discrete cation–counterion hydrogen bonding and a hydrogen-bonded macrocyclic anion–cation–solvent dimer, respectively. Complex 4a contains two unique complex sites, each with internal rotation symmetry, which assemble into 1D hydrogen-bonded chains at 100 K, which persist on warming to RT. Complex 4b also contains two unique cation sites, without internal symmetry, one of which shows a discrete cation–anion hydrogen bond similar to that of 3a, which dissociates on warming. Complex 5c forms a weak hydrogen bond between complex and counterion, whereas 5b does not participate in any hydrogen bonding.

Facial and meridional geometrical isomers of tris(2-methylimidazol-4-yl-methylideneaminobenzyl)iron(II) with Δ- and Λ-configurations and their enantio-discriminative assembly via imidazole⋯chloride hydrogen bonding and spin cross-over properties

A bidentate 2-methylimidazol-4-yl-methylideneaminobenzyl ligand (HLMe-Benz) reacts with FeIICl2·4H2O and NaPF6 at a 3:1:1 molar ratio to yield a tris(2-methylimidazol-4-yl-methylideneaminobenzyl)iron(II) chloride hexafluorophosphate solvate with the formula of [FeII(HLMe-Benz)3]Cl·PF6·solvent. Meridional and facial geometrical isomers, i.e., mer-[FeII (HLMe-Benz)3]Cl·PF6·1.5H2O (1·PF6·1.5H2O) and fac-[FeII(HLMe-Benz)3]Cl·PF6·EtOH·H2O (2·PF6·EtOH·H2O), were selectively crystallized from methanol and ethanol solutions, respectively. fac-[FeII(HLMe-Benz)3]Cl·SbF6·H2O (2·SbF6·H2O) and fac-[FeII(HLMe-Benz)3]Cl·ClO4·EtOH·H2O (2·ClO4·EtOH·H2O) are synthesized in ethanol, using the corresponding anions. Each FeII ion has an octahedral coordination geometry with N6 donor atoms from three bidentate ligands. All three imidazole groups in both the fac- and mer-[FeII(HLMe-Benz)3]2+ cations are hydrogen-bonded to neighboring three Cl− ions, and each Cl− ion is hydrogen-bonded to three imidazole groups of three neighboring complex cations; this results in the formation of hydrogen-bonded assembly structures. mer-Complex 1·PF6·1.5H2O forms a heterochiral two-dimensional (2D) network structure comprised of cyclic {mer-[FeII(HLMe-Benz)3]2+⋯Cl−}3 units with an ΔΔΛ or ΛΛΔ configuration; the PF6− ions occupy the spaces between the 2D layers. All the fac-complexes have isomorphous cubane-like tetrameric structures, i.e., {fac-[FeII(HLMe-Benz)3]2+⋯Cl−}4. The tetranuclear structure comprises four homo-chiral fac-Δ- or fac-Λ-[FeII(HLMe-Benz)3]2+ cations and four Cl− ions interconnected by twelve imidazole-chloride hydrogen bonds to form a chiral cubane supramolecule that encapsulates one counter anion. In the crystal lattice, the cubane-like tetramers with opposite chiralities are alternately arrayed. The temperature dependence of the magnetic susceptibilities and Mössbauer spectra reveal that the fac-complexes show incomplete spin crossover behavior, while the mer-complex shows a gradual spin crossover between high-spin (HS, S=2) and low-spin (LS, S=0) states.

Lattice Effects on the Spin‐Crossover Profile of a Mononuclear Manganese(III) Cation

Six solvated salts of a mononuclear manganese(III) complex with a chelating hexadentate Schiff base ligand are reported. One member of the series, [MnL]PF(6)⋅0.5 CH(3)OH (1), shows a rare low-spin (LS) electronic configuration between 10-300 K. The remaining five salts, [MnL]NO(3)⋅C(2)H(5)OH(2), [MnL]BF(4)⋅C(2)H(5)OH(3), [MnL]CF(3)SO(3)⋅C(2)H(5)OH (4), [MnL]ClO(4)⋅C(2)H(5)OH (5) and [MnL]ClO(4)⋅0.5 CH(3)CN (6), all show gradual incomplete spin-crossover (SCO) behaviour. The structures of all were determined at 100 K, and also at 293 K in the case of 3-6. The LS salt [MnL]PF(6)⋅0.5 CH(3)OH is the only member of the series that does not exhibit strong hydrogen bonding. At 100 K two of the four SCO complexes (2 and 4) assemble into 1D hydrogen-bonded chains, which weaken or rupture on warming. The remaining SCO complexes 3, 5 and 6 do not form 1D hydrogen-bonded chains, but instead exhibit discrete hydrogen bonding between cation/counterion, cation/solvent or counterion/solvent and show no significant change on warming.