Mixed valency in polynuclear MnII/MnIII, MnIII/MnIV and MnII/MnIII/MnIV clusters: a foundation for high-spin molecules and single-molecule magnets

Templated Growth of a Spin-Frustrated Cluster Fragment of MnBr2 in a Metal-Organic Framework

The metal-organic framework Zr₆O₄(OH)₄(bpydc)₆ (bpydc^2- = 2,2'-bipyridine-5,5'-dicarboxylate) is used to template the growth of a cluster fragment of the two-dimensional solid MnBr₂, which was predicted to exhibit spin frustration. Single-crystal and powder X-ray diffraction analyses reveal a cluster with 19 metal ions arranged in a triangular lattice motif. Static magnetic susceptibility measurements indicate antiferromagnetic coupling between the high-spin (S = ⁵/₂) Mn^II centers, and dynamic magnetic susceptibility data suggest population of low-lying excited states, consistent with magnetic frustration. Density functional theory calculations are used to determine the energies for a subset of thousands of magnetic configurations available to the cluster. The Yamaguchi generalized spin-projection method is then employed to construct a model for magnetic coupling interactions within the cluster, enabling facile determination of the energy for all possible magnetic configurations. The confined cluster is predicted to possess a doubly degenerate, highly geometrically frustrated ground state with a total spin of S_Total = ⁵/₂.

Structure, DFT studies and evaluation of catechol oxidase (CO) mimic activity of mononuclear Co(II) complexes derived from aminoalcohols: an experimental and theoretical approach

The impetus to modeling of enzyme mimics comes from their potential to provide insight to the alternate mechanistic pathways of the native enzymes. The present study demonstrates the syntheses and characterization of two different cobalt(II) complexes, [Co(pdm)(Phen)Cl]Cl·H₂O (1) and [Co(pmmH)₂(SCN)₂] (2) with the aminoalcohol ligands such as pyridine-2,6-dimethanol (pdmH₂) or 2-pyridinemonomethanol (pmmH) and their assessment as catechol oxidase (CO) enzyme mimic. Single Crystal X-ray diffraction and powder X-ray diffraction data suggest the octahedral environment around the Co(II) ion and the complexes form extensive 1D or 2D propagating network as a result of non-covalent interactions (O···H and C-H···π). TD-DFT calculations were used to explain the spectral bands obtained during the UV-Vis absorption studies and it is ascertained that the transitions were mainly of the intra-ligand charge transfer (ILCT) type. The catecholase biomimetic catalytic activity of the synthesized complexes has been investigated in detail and the kinetics is also performed. The results obtained show that both the complexes catalyze the aerobic oxidation of catechol to the corresponding o-quinone. The K_cat value for 1 is 106.99 h^‒1 and for 2 is 90.32 h^‒1 in methanol. It may be mentioned here that 1 and 2 are effective catalysts, with the order of activity being 1 > 2. The order of enzymatic activity is well justified by CV and DFT studies.Communicated by Ramaswamy H. Sarma.

'Metal Complexes as Ligands' for the Synthesis of Coordination Polymers: A MnIII Monomer as a Building Block for the Preparation of an Unprecedented 1-D {MnIIMnIII}n Linear Chain

A relatively unexplored synthetic route in redox-active Mn(II/III) coordination chemistry has been employed toward the preparation of a new mixed-valence Mn^II/III 1-D linear chain from the reaction of [Mn^III(sacb)₂]⁻ precursor with a Mn^II source, where sacbH₂ is the Schiff base ligand N-salicylidene-2-amino-5-chlorobenzoic acid. The mononuclear (Pr₂NH₂)[Mn^III(sacb)₂] (1) compound was obtained in excellent yields (>85%) from the 1:2:3 reaction of Mn(O₂CMe)₂∙4H₂O, sacbH₂ and Pr₂NH, respectively. In 1, the two doubly deprotonated sacb²⁻ ligands act as O_carboxylate,N_imine,O_phenoxide-tridentate chelates, while the second carboxylate O atom of sacb²⁻ is dangling and H-bonded to the Pr₂NH₂⁺ countercation. Complex 1 was subsequently used as a ‘ligand’ to react stoichiometrically with the ‘metal’ Mn(NO₃)₂∙4H₂O, thus leading to the 1-D coordination polymer {[Mn^IIMn^III(sacb)₂(H₂O)₂(MeOH)₂](NO₃)}_n (2) in good yields (~50%). The removal of Pr₂NH₂⁺ from the vicinity of the [Mn^III(sacb)₂]⁻ metalloligand has rendered possible (vide infra) the coordination of the second O_carboxylate of sacb²⁻ to neighboring {Mn^II(H₂O)₂(MeOH)₂}²⁺ units, and consequently the formation of the 1-D polymer 2. Direct-current (dc) magnetic susceptibility studies revealed the presence of very weak antiferromagnetic exchange interactions between alternating Mn^III and Mn^II atoms with a coupling constant of J = −0.08 cm⁻¹ for g = 2.00. The combined results demonstrate the potential of the ‘metal complexes as ligands’ approach to yield new mixed-valence Mn(II/III) coordination polymers with interesting structural motifs and physicochemical properties.

Exploring solvent dependent catecholase activity in transition metal complexes: an experimental and theoretical approach

Four coordination compounds are designed with pyridinemethanol ligands, characterized with spectral, magnetic and X-ray analyses, and assessed for catecholase activity in various solvents.

Organic chelate-free and azido-rich metal clusters and coordination polymers from the use of Me3SiN3: a new synthetic route to complexes with beautiful structures and diverse magnetic properties

A new synthetic route to structurally novel and magnetically interesting 3d-metal azido clusters and coordination polymers is presented; the key reagent for the preparation of solely azido-bridged molecule-based species is the organic azide precursor Me₃SiN₃.

Transition Metal Single-Molecule Magnets: A {Mn31} Nanosized Cluster with a Large Energy Barrier of ∼60 K and Magnetic Hysteresis at ∼5 K

The first {Mn₃₁} cluster (1) has been prepared from carboxylate ions and the chelating/bridging ligand α-methyl-2-pyridine-methanol. Compound 1 possesses a unique nanosized structural topology with one of the largest energy barriers reported to-date for high-nuclearity 3d-metal clusters. Single-crystal magnetic hysteresis studies reveal the presence of hysteresis loops below 5 K, one of the highest temperatures below which molecular hysteresis has been observed for 3d-based SMMs.

Switchable Multiple Spin States in the Kondo description of Doped Molecular Magnets

We show that introducing electrons in magnetic clusters and molecular magnets lead to rich phase diagrams with a variety of low-spin and high-spin states allowing for multiple switchability. The analysis is carried out for a quantum spin-fermion model using the exact diagonalization, and the cluster mean-field approach. The model is relevant for a number of molecular magnets with triangular motifs consisting of transition metal ions such as Cr, Cu and V. Re-entrant spin-state behavior and chirality on-off transitions exist over a wide parameter regime. A subtle competition among geometrical frustration effects, electron itinerancy, and Kondo coupling at the molecular level is highlighted. Our results demonstrate that electron doping provides a viable mean to tame the magnetic properties of molecular magnets towards potential technological applications.

Enhancement of Tb(III) -Cu(II) Single-Molecule Magnet Performance through Structural Modification

We report a series of 3d-4f complexes {Ln2 Cu3 (H3 L)2 Xn } (X=OAc(-) , Ln=Gd, Tb or X=NO3 (-) , Ln=Gd, Tb, Dy, Ho, Er) using the 2,2'-(propane-1,3-diyldiimino)bis[2-(hydroxylmethyl)propane-1,3-diol] (H6 L) pro-ligand. All complexes, except that in which Ln=Gd, show slow magnetic relaxation in zero applied dc field. A remarkable improvement of the energy barrier to reorientation of the magnetisation in the {Tb2 Cu3 (H3 L)2 Xn } complexes is seen by changing the auxiliary ligands (X=OAc(-) for NO3 (-) ). This leads to the largest reported relaxation barrier in zero applied dc field for a Tb/Cu-based single-molecule magnet. Ab initio CASSCF calculations performed on mononuclear Tb(III) models are employed to understand the increase in energy barrier and the calculations suggest that the difference stems from a change in the Tb(III) coordination environment (C4v versus Cs ).

New structural motifs in Mn cluster chemistry from the ketone/gem-diol and bis(gem-diol) forms of 2,6-di-(2-pyridylcarbonyl)pyridine: {MnII4MnIII2} and {MnII4MnIII6} complexes

The ketone/gem-diol (L1H₂) and bis(gem-diol) (L2H₄) forms of the ligand 2,6-di-(2-pyridylcarbonyl)pyridine in Mn cluster chemistry have afforded the new complexes [MnII4MnIII2(N₃)₆Cl₄(L1)₂(DMF)₄] and [MnII4MnIII6O₂(N₃)₁₂(L1)₂(L2H)₂(DMF)₆].

Metal oxidation states in biological water splitting

A central question in biological water splitting concerns the oxidation states of the manganese ions that comprise the oxygen-evolving complex of photosystem II.

A central question in biological water splitting concerns the oxidation states of the manganese ions that comprise the oxygen-evolving complex of photosystem II. Understanding the nature and order of oxidation events that occur during the catalytic cycle of five S_i states (i = 0–4) is of fundamental importance both for the natural system and for artificial water oxidation catalysts. Despite the widespread adoption of the so-called “high-valent scheme”—where, for example, the Mn oxidation states in the S₂ state are assigned as III, IV, IV, IV—the competing “low-valent scheme” that differs by a total of two metal unpaired electrons (i.e. III, III, III, IV in the S₂ state) is favored by several recent studies for the biological catalyst. The question of the correct oxidation state assignment is addressed here by a detailed computational comparison of the two schemes using a common structural platform and theoretical approach. Models based on crystallographic constraints were constructed for all conceivable oxidation state assignments in the four (semi)stable S states of the oxygen evolving complex, sampling various protonation levels and patterns to ensure comprehensive coverage. The models are evaluated with respect to their geometric, energetic, electronic, and spectroscopic properties against available experimental EXAFS, XFEL-XRD, EPR, ENDOR and Mn K pre-edge XANES data. New 2.5 K ⁵⁵Mn ENDOR data of the S₂ state are also reported. Our results conclusively show that the entire S state phenomenology can only be accommodated within the high-valent scheme by adopting a single motif and protonation pattern that progresses smoothly from S₀ (III, III, III, IV) to S₃ (IV, IV, IV, IV), satisfying all experimental constraints and reproducing all observables. By contrast, it was impossible to construct a consistent cycle based on the low-valent scheme for all S states. Instead, the low-valent models developed here may provide new insight into the over-reduced S states and the states involved in the assembly of the catalytically active water oxidizing cluster.

Switching nuclearity and Co(ii) content through stoichiometry adjustment: {CoII6CoIII3} and {CoIICo4III} mixed valent complexes and a study of their magnetic properties

Controlling the Co^II content in polynuclear systems: {Co^II₆Co^III₃} and {Co^IICo₄^III} mixed valent complexes with distinct magnetic behaviours is reported.

Two-dimensional molecular magnets with weak topological invariant magnetic moments: mathematical prediction of targets for chemical synthesis

An open problem in applied mathematics is to predict interesting molecules that are realistic targets for chemical synthesis. In this paper, we use a spin Hamiltonian-type model to predict molecular magnets (MMs) with magnetic moments that are intrinsically robust under random shape deformations to the molecule. Using the concept of convergence in probability, we show that for MMs in which all spin centres lie in-plane and all spin centre interactions are ferromagnetic, the total spin of the molecule is a 'weak topological invariant' when the number of spin centres is sufficiently large. By weak topological invariant, we mean that the total spin of the molecule depends only upon the arrangement of spin centres in the molecule, and is unlikely to change under shape deformations to the molecule. Our calculations show that only between 20 and 50 spin centres are necessary for the total spin of these MMs to be a weak topological invariant. The robustness effect is particularly enhanced for two-dimensional ferromagnetic MMs that possess a small number of spin rings in the structure.

Role of Oxido Incorporation and Ligand Lability in Expanding Redox Accessibility of Structurally Related Mn4 Clusters

Photosystem II supports four manganese centers through nine oxidation states from manganese(II) during assembly through to the most oxidized state before O₂ formation and release. The protein-based carboxylate and imidazole ligands allow for significant changes of the coordination environment during the incorporation of hydroxido and oxido ligands upon oxidation of the metal centers. We report the synthesis and characterization of a series of tetramanganese complexes in four of the six oxidation states from Mn^II₃Mn^III to Mn^III₂ Mn^IV₂ with the same ligand framework (L) by incorporating four oxido ligands. A 1,3,5-triarylbenzene framework appended with six pyridyl and three alkoxy groups was utilized along with three acetate anions to access tetramanganese complexes, Mn₄O _x , with x = 1, 2, 3, and 4. Alongside two previously reported complexes, four new clusters in various states were isolated and characterized by crystallography, and four were observed electrochemically, thus accessing the eight oxidation states from Mn^II₄ to Mn^IIIMn^IV₃. This structurally related series of compounds was characterized by EXAFS, XANES, EPR, magnetism, and cyclic voltammetry. Similar to the ligands in the active site of the protein, the ancillary ligand (L) is preserved throughout the series and changes its binding mode between the low and high oxido-content clusters. Implications for the rational assembly and properties of high oxidation state metal-oxido clusters are presented.

Comproportionation reactions to manganese(III/IV) pivalate clusters: a new half-integer spin single-molecule magnet

The comproportionation reaction between Mn(II) and Mn(VII) reagents under acidic conditions has been investigated in the presence of pivalic acid as a route to new high oxidation state manganese pivalate clusters containing some Mn(IV). The reaction of Mn(O(2)CBu(t))(2) and NBu(n)(4)MnO(4) with an excess of pivalic acid in the presence of Mn(ClO(4))(2) and NBu(n)(4)Cl in hot MeCN led to the isolation of [Mn(8)O(6)(OH)(O(2)CBu(t))(9)Cl(3)(Bu(t)CO(2)H)(0.5)(MeCN)(0.5)] (1). In contrast, the reaction of Mn(NO(3))(2) and NBu(n)(4)MnO(4) in hot MeCN with an excess of pivalic acid gave a different octanuclear complex, [Mn(8)O(9)(O(2)CBu(t))(12)] (2). The latter reaction but with Mn(O(2)CBu(t))(2) in place of Mn(NO(3))(2), and in a MeCN/THF solvent medium, gave [Mn(9)O(7)(O(2)CBu(t))(13)(THF)(2)] (3). Complexes 1-3 possess rare or unprecedented Mn(x) topologies: 1 possesses a [Mn(III)(7)Mn(IV)(μ(3)-O)(4)(μ(4)-O)(2)(μ(3)-OH)(μ(4)-Cl)(μ(2)-Cl)](8+) core consisting of two body-fused Mn(4) butterfly units attached to the remaining Mn atoms via bridging O(2-), OH(-), and Cl(-) ions. In contrast, 2 possesses a [Mn(6)(IV)Mn(2)(III)(μ(3)-O)(6)(μ-O)(3)](12+) core consisting of two [Mn(3)O(4)] incomplete cubanes linked by their O(2-) ions to two Mn(III) atoms. The cores of 1 and 2 are unprecedented in Mn chemistry. The [Mn(III)(9)(μ(3)-O)(7)](13+) core of 3 also contains two body-fused Mn(4) butterfly units, but they are linked to the remaining Mn atoms in a different manner than in 1. Solid-state direct current (dc) and/or alternating current (ac) magnetic susceptibility data established S = (15)/(2), S = 2, and S = 1 ground states for 1·MeCN, 2·(1)/(4)MeCN, and 3, respectively. The ac susceptibility data also revealed nonzero, frequency-dependent out-of-phase (χ″(M)) signals for 1·MeCN at temperatures below 3 K, suggesting possible single-molecule magnet behavior, which was confirmed by single-crystal magnetization vs dc field scans that exhibited hysteresis loops. The combined work thus demonstrates the continuing potential of comproportionation reactions for isolating high oxidation state Mn(x) clusters, and the sensitivity of the product identity to minor changes in the reaction conditions.

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.

Carboxylate-free Mn(III)2Ln(III)2 (Ln = lanthanide) and Mn(III)2Y(III)2 complexes from the use of (2-hydroxymethyl)pyridine: analysis of spin frustration effects

The initial employment of 2-(hydroxymethyl)pyridine for the synthesis of Mn/Ln (Ln = lanthanide) and Mn/Y clusters, in the absence of an ancillary organic ligand, has afforded a family of tetranuclear [Mn(III)(2)M(III)(2)(OH)(2)(NO(3))(4)(hmp)(4)(H(2)O)(4)](NO(3))(2) (M = Dy, 1; Tb, 2; Gd, 3; Y; 4) anionic compounds. 1-4 possess a planar butterfly (or rhombus) core and are rare examples of carboxylate-free Mn/Ln and Mn/Y clusters. Variable-temperature dc and ac studies established that 1 and 2, which contain highly anisotropic Ln(III) atoms, exhibit slow relaxation of their magnetization vector. Fitting of the obtained magnetization (M) versus field (H) and temperature (T) data for 3 by matrix diagonalization and including only axial anisotropy (zero-field splitting, ZFS) showed the ground state to be S = 3. Complex 4 has an S = 0 ground state. Fitting of the magnetic susceptibility data collected in the 5-300 K range for 3 and 4 to the appropriate van Vleck equations revealed, as expected, extremely weak antiferromagnetic interactions between the paramagnetic ions; for 3, J(1) = -0.16(2) cm(-1) and J(2) = -0.12(1) cm(-1) for the Mn(III)···Mn(III) and Mn(III)···Gd(III) interactions, respectively. The S = 3 ground state of 3 has been rationalized on the basis of the spin frustration pattern in the molecule. For 4, J = -0.75(3) cm(-1) for the Mn(III)···Mn(III) interaction. Spin frustration effects in 3 have been quantitatively analyzed for all possible combinations of sign of J(1) and J(2).

Combining azide, carboxylate, and 2-pyridyloximate ligands in transition-metal chemistry: ferromagnetic Ni(II)5 clusters with a bowtie skeleton

The combined use of the anion of phenyl(2-pyridyl)ketone oxime (ppko(-)) and azides (N(3)(-)) in nickel(II) carboxylate chemistry has afforded two new Ni(II)(5) clusters, [Ni(5)(O(2)CR')(2)(N(3))(4)(ppko)(4)(MeOH)(4)] [R' = H (1), Me (2)]. The structurally unprecedented {Ni(5)(μ-N(3))(2)(μ(3)-N(3))(2)}(6+) cores of the two clusters are almost identical and contain the five Ni(II) atoms in a bowtie topology. Two N(3)(-) ions are end-on doubly bridging and the other two ions end-on triply bridging. The end-on μ(3)-N(3)(-) groups link the central Ni(II) atoms with the two peripheral metal ions on either side of the molecule, while the Ni···Ni bases of the triangles are each bridged by one end-on μ-N(3)(-) group. Variable-temperature, solid-state direct- (dc) and alternating-current (ac) magnetic susceptibility, and magnetization studies at 2.0 K were carried out on both complexes. The data indicate an overall ferromagnetic behavior and an S = 5 ground state for both compounds. The ac susceptibility studies on 1 reveal nonzero, frequency-dependent out-of-phase (χ(M)") signals at temperatures below ~3.5 K; complex 2 reveals no χ(M)" signals. However, single-crystal magnetization versus dc field scans at variable temperatures and variable sweep rates down to 0.04 K on 1 reveal no noticeable hysteresis loops, except very minor ones at 0.04 K assignable to weak intermolecular interactions propagated by nonclassical hydrogen bonds.

Unusual structural types in nickel cluster chemistry from the use of pyridyl oximes: Ni5, Ni12Na2, and Ni14 clusters

Syntheses, crystal structures, and magnetochemical characterization are reported for the three new nickel(II) clusters [Ni(14)(OH)(4)(N(3))(8)(pao)(14)(paoH)(2)(H(2)O)(2)](ClO(4))(2) (1), [Ni(12)Na(2)(OH)(4)(N(3))(8)(pao)(12)(H(2)O)(10)](OH)(2) (2), and [Ni(5)(ppko)(5)(H(2)O)(7)](NO(3))(5) (3) (paoH = pyridine-2-carbaldehyde oxime, ppkoH = di-2-pyridyl ketone oxime). The reaction of Ni(ClO(4))(2).6H(2)O with paoH and NBu(n)(4)N(3) in H(2)O/MeCN in the presence of NEt(3), gave 1 in 65% yield. Complex 2 was obtained in 60% yield from the reaction of NiCl(2).6H(2)O with paoH and NaN(3) in H(2)O/MeCN in the presence of NaOH. The reaction of Ni(NO(3))(2).6H(2)O with ppkoH in EtOH in the presence of LiOH afforded complex 3 in 75% yield. The complexes all contain novel core topologies. The core of 1 comprises a central Ni(4) rhombus between two Ni(5). Complex 1 is the largest metal/oxime cluster discovered to date, as well as the first Ni(II)(14) coordination complex and the largest Ni(II)/N(3)(-) cluster. Complex 2 has a Ni(12)Na(2) topology that is very similar to that of 1, but with two central Ni(II) atoms of 1 replaced with Na(I) atoms. The core of 3 consists of four Ni(II) atoms forming a highly distorted tetrahedron, with the fifth Ni(II) atom lying almost on one of the edges. Variable-temperature, solid-state dc susceptibility and magnetization studies were carried out on complexes 1-3, and these were complemented with ac susceptibility data for 1 and 2. Fitting of the obtained M/(Nmu(B)) vs H/T data by matrix diagonalization and including axial zero-field splitting (D) gave ground-state spin (S) and D values of S = 6, D = -0.12(3) cm(-1) for 1 and S = 3, D = -0.20(5) cm(-1) for each of the two essentially noninteracting S = 3 Ni(6) subunits of 2. The data for 3 indicate antiferromagnetic exchange interactions and an S = 1 ground state. A simple 2-J model was found to be adequate to describe the variable-temperature dc susceptibility data. The combined work demonstrates the ligating flexibility of pao(-) and ppko(-), and their usefulness in the synthesis of polynuclear Ni(x) clusters with or without the presence of ancillary ligands.

Azide groups in higher oxidation state manganese cluster chemistry: from structural aesthetics to single-molecule magnets

This Forum Article overviews the recent amalgamation of two long-established areas, manganese/oxo coordination cluster chemistry involving the higher Mn(II)/Mn(IV) oxidation states and transition-metal azide (N(3)(-)) chemistry. The combination of azide and alkoxide- or carboxylate-containing ligands in Mn chemistry has led to a variety of new polynuclear clusters, high-spin molecules, and single-molecule magnets, with metal nuclearities ranging from Mn(4) to Mn(32) and with ground-state spin values as large as S = 83/2. The organic bridging/chelating ligands are discussed separately as follows: (i) pyridyl alkoxides [the anions of 2-(hydroxymethyl)pyridine (hmpH), 2,6-pyridinedimethanol (pdmH(2)), and the gem-diol form of di-2-pyridyl ketone (dpkdH(2))]; (ii) non-pyridyl alkoxides [the anions of 1,1,1-tris(hydroxymethyl)ethane (thmeH(3)), triethanolamine (teaH(3)), and N-methyldiethanolamine (mdaH(2))]; (iii) other alcohols [the anions of 2,6-dihydroxymethyl-4-methylphenol (LH(3)) and Schiff bases]; (iv) pyridyl monoximes/dioximes [the anions of methyl-2-pyridyl ketone oxime (mpkoH), phenyl-2-pyridyl ketone oxime (ppkoH), and 2,6-diacetylpyridine dioxime (dapdoH(2))]; (v) non-pyridyl oximes [the anions of salicylaldoxime (saoH(2)) and its derivatives R-saoH(2)]. The large structural diversity of the resulting complexes stems from the combined ability of the azide and organic ligands to adopt a variety of ligation and bridging modes. The combined work demonstrates the synthetic novelty that arises when azide is used in conjunction with alcohol-based chelates, the aesthetic beauty of the resulting molecules, and the often fascinating magnetic properties that these compounds possess. This continues to emphasize the extensive and remarkable ability of Mn chemistry to satisfy a variety of different tastes.

The Drosophila of single-molecule magnetism: [Mn12O12(O2CR)16(H2O)4]

Single-molecule magnets (SMMs) are individual molecules that can function as nanoscale magnetic particles. The [Mn12O12(O2CR)16(H2O)4] (Mn12; R=Me, Et, etc.) family of SMMs was the first one discovered; it is also the one whose study has provided the majority of current knowledge on this interesting magnetic phenomenon, prompting its description here as the Drosophila of the field. This tutorial review will survey the various chemical studies that have been carried out to date on this family. This will include a discussion of methods that have been developed for their structural and redox transformation, and the effect of the latter on the magnetic and SMM properties.