Syntheses, Structures and Magnetic Properties of Two Mixed-Valent Disc-like Hepta-nuclear Compounds of [FeIIFeIII6(tea)6](ClO4)2 and [MnII3MnIII4(nmdea)6(N3)6]·CH3OH (tea = N(CH2CH2O)33−,nmdea = CH3N(CH2CH2O)22−)

Triethanolaminate iron perchlorate revisited: change of space group, chemical composition and oxidation states in [Fe7(tea)3(tea-H)3](ClO4)2 (tea-H3 is triethanolamine)

The X-ray crystal structure of tris[N-(2-hydroxyethyl)-2,2'-iminodiethanolato]tris(2,2',2''-nitrilotriethanolato)tetrairon(II)triiron(III) bis(perchlorate), [Fe₇(C₆H₁₂NO₃)₃(C₆H₁₃NO₃)₃](ClO₄)₂ or [Fe₇(tea)₃(tea-H)₃](ClO₄)₂ (tea-H₃ is triethanolamine), is known from the literature [Liu et al. (2008). Z. Anorg. Allg. Chem. 634, 778-783] as a heptanuclear coordination cluster. The space group was given as I2₁3 and is reinvestigated in the present study. We find a new space-group symmetry of Pa-3 and could detect O-H hydrogens, which were missing in the original publication. Consequences on the Fe oxidation states are investigated with the bond-valence method, resulting in a mixed-valence core of four Fe^II and three Fe^III centres. Symmetry relationships between the two space groups and the average supergroup Ia-3 are discussed in detail.

A one dimensional coordination polymer composed of antiferromagnetically coupled disk-like [Mn7] units

A single-chain magnet (SCM) was constructed from disk-like Mn₇ clusters linked by azide units.

Structural isomers of iron(iii) N-methyl diethanolaminate as sol–gel precursors for iron-based oxide nanomaterials

New aminoalkoxides of Fe(iii) were synthesized, evaluated for different sol–gel parameters to stabilize nano-sized colloidal suspensions, and employed for the elaboration of magnetic Fe₂O₃ and BiFeO₃ NPs and thin films.

Magnetic Behavior of Heterometallic Wheels Having a [Mn(IV)6M2O9](10+) Core with M = Ca(2+) and Sr(2+)

Two new heterometallic Mn(IV)-M(2+) compounds with formula [Mn6M2O9(4-(t)BuC6H4COO)10(4-(t)BuC6H4COOH)5] (M = Ca(2+) (1), Sr(2+) (2)) have been crystallized. The core of both compounds consists of a planar Mn6 ring, where the Mn(IV) ions are alternatively bridged by (μ3-O)2(μ-RCOO) and (μ4-O)(μ-RCOO)2 ligands, and the two alkaline earth ions are located to both sides of the wheel, linked to the oxo bridges, generating three fused [Mn2M2O4](4+) cuboids. These compounds show a net antiferromagnetic behavior, more important for 2 (Sr(2+)) than for 1 (Ca(2+)). The fitting of the experimental data was performed with the support of DFT calculations, considering four different exchange pathways: two between adjacent Mn(IV) ions (J1 and J2) and two between nonadjacent Mn(IV) ions (J3 and J4). The results of the analysis show that J1 and J2 are of the opposite sign, the ferromagnetic contribution corresponding to the [Mn2(μ4-O)(μ-RCOO)2](4+) unit (J2). The influence of the M(2+) ions in the magnetic behavior is analyzed for 1 and 2 and for three hypothetical models with the structural parameters of 1 containing Mg(2+), Sr(2+) or without the M(2+) ions. In spite of the diamagnetic character of the alkaline earth ions, their influence on the magnetic behavior has been evidenced and correlated with their polarizing effect. Moreover, the magnetic interactions between nonadjacent ions are non-negligible.

What controls the magnetic exchange interaction in mixed- and homo-valent Mn7 disc-like clusters? A theoretical perspective

Density functional theory (DFT) studies have been undertaken to compute the magnetic exchange and to probe the origin of the magnetic interactions in two hetero- and two homo-valent heptanuclear manganese disc-like clusters, of formula [Mn(II) 4 Mn(IV) 3 (tea)(teaH2 )3 (peolH)4 ] (1), [Mn(II) 4 Mn(III) 3 F3 (tea)(teaH)(teaH2 )2 (piv)4 (Hpiv)(chp)3 ] (2), [Mn(II) 7 (pppd)6 (tea)(OH)3 ] (3) and [Mn(II) 7 (paa)6 (OMe)6 ] (4) (teaH3 =triethanolamine, peolH4 =pentaerythritol, Hpiv=pivalic acid, Hchp=6-chloro-2-hydroxypyridine, pppd=1-phenyl-3-(2-pyridyl) propane-1,3-dione; paaH=N-(2-pyridinyl)acetoacetamide). DFT calculations yield J values, which reproduce the magnetic susceptibility data very well for all four complexes; these studies are also highlighting the likely ageing/stability problems in two of the complexes. It is found that the spin ground states, S, for complexes 1-4 are drastically different, varying from S=29/2 to S=1/2. These values are found to be controlled by the nature of the oxidation state of the metal ions and minor differences present in the structures. Extensive magneto-structural correlations are developed for the seven building unit dimers present in the complexes, with the correlations unlocking the reasons behind the differences in the magnetic properties observed. Independent of the oxidation state of the metal ions, the Mn-O-Mn/Mn-F-Mn angles are found to be the key parameters, which significantly influence the sign as well as the magnitude of the J values. The magneto-structural correlations developed here, have broad applicability and can be utilised to understand the magnetic properties of other Mn clusters.

Structural variation from heterometallic heptanuclear or heptanuclear to cubane clusters based on 2-hydroxy-3-ethoxy-benzaldehyde: effects of pH and temperature

Five novel clusters were reported, with results showing that pH and reaction temperatures have a key role in the self-assembly process.

Heptanuclear antiferromagnetic Fe(III)-D-(-)-quinato assemblies with an S = 3/2 ground state-pH-specific synthetic chemistry, spectroscopic, structural, and magnetic susceptibility studies

Iron is an essential metal ion with numerous roles in biological systems and advanced abiotic materials. D-(-)-quinic acid is a cellular metal ion chelator, capable of promoting reactions with metal M(II,III) ions under pH-specific conditions. In an effort to comprehend the chemical reactivity of well-defined forms of Fe(III)/Fe(II) toward α-hydroxycarboxylic acids, pH-specific reactions of: (a) [Fe3O(CH3COO)6(H2O)3]·(NO3)·4H2O with D-(-)-quinic acid in a molar ratio 1:3 at pH 2.5 and (b) Mohr's salt with D-(-)-quinic acid in a molar ratio 1:3 at pH 7.5, respectively, led to the isolation of the first two heptanuclear Fe(III)-quinato complexes, [Fe7O3(OH)3(C7H10O6)6]·20.5H2O (1) and (NH4)[Fe7(OH)6(C7H10O6)6]·(SO4)2·18H2O (2). Compounds 1 and 2 were characterized by analytical, spectroscopic (UV-vis, FT-IR, EPR, and Mössbauer) techniques, CV, TGA-DTG, and magnetic susceptibility measurements. The X-ray structures of 1 and 2 reveal heptanuclear assemblies of six Fe(III) ions bound by six doubly deprotonated quinates and one Fe(III) ion bound by oxido- and hydroxido-bridges (1), and hydroxido-bridges (2), all in an octahedral fashion. Mössbauer spectroscopy on 1 and 2 suggests the presence of Fe(III) ions in an all-oxygen environment. EPR measurements indicate that 1 and 2 retain their structure in solution, while magnetic measurements reveal an overall antiferromagnetic behavior with a ground state S = 3/2. The collective physicochemical properties of 1 and 2 suggest that the (a) nature of the ligand, (b) precursor form of iron, (c) pH, and (d) molecular stoichiometry are key factors influencing the chemical reactivity of the binary Fe(II,III)-hydroxycarboxylato systems, their aqueous speciation, and ultimately through variably emerging hydrogen bonding interactions, the assembly of multinuclear Fe(III)-hydroxycarboxylato clusters with distinct lattice architectures of specific dimensionality (2D-3D) and magnetic signature.

Unusual oxidation state distributions observed for two mixed-valence heptanuclear manganese disc-like clusters

The synthesis, structures and magnetic properties of two new mixed-valence heptanuclear manganese clusters are described. Both complexes utilize triethanolamine (teaH(3)) as a bridging ligand, displaying near planar, disc-like metal topologies and are of formulae [Mn(II)(4)Mn(IV)(3)(tea)(teaH(2))(3)(peolH)(4)](BF(4))(2)·solv (1) and [Mn(II)(4)Mn(III)(3)F(3)(tea)(teaH)(teaH(2))(2)(piv)(4)(Hpiv)(chp)(3)]·0.5MeCN (2). Compound 1 is a rare mixed-valence compound containing Mn(II) and Mn(IV) ions only and is the first example of a heptanuclear disc with a {Mn(II)(4)Mn(IV)(3)} oxidation state distribution. Compound 2 is a {Mn(II)(4)Mn(III)(3)} complex and displays a unique arrangement of oxidation states within the disc, when compared to other known {Mn(II)(4)Mn(III)(3)} examples. Variable temperature DC and AC magnetic susceptibility studies were carried out for 1 and 2 in the 2-300 K temperature range. Compound 1 displayed an increase in the χ(M)T susceptibility values as the temperature is decreased indicating dominant ferromagnetic interactions are present within the cluster. Fits of the χ(M)T vs. T data reveals an S = 23/2 ground state, with several close lying excited states within 1 cm(-1). Compound 2 displays an overall decrease in the χ(M)T value as the temperature is decreased down to 2 K indicating dominant antiferromagnetic interactions present with a probable S = 4 ground state as determined from the DC and AC susceptibility data.

Azido-{2-[bis-(2-hy-droxy-eth-yl)amino]-ethano-lato-κN,O,O',O''}cobalt(II)

In the title complex, [Co(C₆H₁₄NO₃)(N₃)] or [Co(teaH₂)N₃], the Co^II atom resides in a trigonal–bipymidal O₃N₂ environment formed by three O atoms and one N atom from a simply deprotonated tetra­dentate triethano­lamine ligand, and one N atom from an azide ligand. The O atoms define the equatorial plane whereas both N atoms are in axial positions. The mononuclear units are linked through O—H⋯O hydrogen-bonding inter­actions between the ethanol OH groups and the ethano­late O atom of a neighbouring complex into chains running parallel to [010].