11 research outputs found
Crossover from Antiferromagnetic to Ferromagnetic Exchange Coupling in a New Family of Bis-(Ī¼-phenoxido)dicopper(II) Complexes: A Comprehensive MagnetoāStructural Correlation by Experimental and Theoretical Study
International audienc
Pentanuclear 3d-4f heterometal complexes of MII3LnIII2 (M = Ni, Cu, Zn and Ln = Nd, Gd and Tb) combinations: syntheses, structures, magnetism and photoluminescence properties
A new family of pentanuclear 3d-4f heterometal complexes of general composition [LnIII2(MIIL)3(Ī¼3-O)3H](ClO4)Ā·xH2O (1-5) [Ln = Nd, M = Zn, 1; Nd, Ni, 2; Nd, Cu, 3; Gd, Cu, 4; Tb, Cu, 5] have been synthesized in moderate yields (50-60%) following a self-assembly reaction involving the hexadentate phenol-based ligand, viz., N,N-bis(2-hydroxy-3-methoxy-5-methylbenzyl)-Nā²,Nā²-diethylethylenediamine (H2L). Single-crystal X-ray diffraction analyses have been used to characterize these complexes. The compounds are all isostructural, having a 3-fold axis of symmetry that passes through the 4f metal centers. The [MIIL] units in these complexes are acting as bis-bidentate metalloligands and, together with Ī¼3-oxido bridging ligands, complete the slightly distorted monocapped square antiprismatic nine-coordination environment around the 4f metal centers. The cationic complexes also contain a H+ ion that occupies the central position at the 3-fold axis. Magnetic properties of the copper(II) complexes (3-5) show a changeover from antiferromagnetic in 3 to ferromagnetic 3d-4f interactions in 4 and 5. For the isotropic CuII-GdIII compound 4, the simulation of magnetic data provides very weak Cu-Gd (J1 = 0.57 cm-1) and Gd-Gd exchange constants (J2 = 0.14 cm-1). Compound 4 is the only member of this triad, showing a tail of an out-of-phase signal in the ac susceptibility measurement. A large-spin ground state (S = 17/2) and a negative value of D (-0.12 cm-1) result in a very small barrier (8 cm-1) for this compound. Among the three NdIII2MII3 (M = ZnII, NiII, and CuII) complexes, only the ZnII analogue (1) displays an NIR luminescence due to the 4F3/2 ā 4I11/2 transition in NdIII when excited at 290 nm. The rest of the compounds do not show such NdIII/TbIII-based emission. The paramagnetic CuII and NiII ions quench the fluorescence in 2-5 and thereby lower the population of the triplet stat
Heterobimetallic Ī¼āOxido Complexes Containing Discrete V<sup>V</sup>āOāM<sup>III</sup> (M = Mn, Fe) Cores: Targeted Synthesis, Structural Characterization, and Redox Studies
Heterobimetallic compounds [Lā²OV<sup>V</sup>(Ī¼-O)ĀM<sup>III</sup>L]<sub><i>n</i></sub> (<i>n</i> = 1, M = Mn, <b>1</b>ā<b>5</b>; <i>n</i> = 2, M = Fe, <b>6</b> and <b>7</b>) containing
a discrete unsupported V<sup>V</sup>āOāM<sup>III</sup> bridge have been synthesized through a targeted synthesis route.
In the VāOāMn-type complexes, the vanadiumĀ(V) centers
have a square-pyramidal geometry, completed by a dithiocarbazate-based
tridentate Schiff-base ligand (H<sub>2</sub>Lā²), while the
manganeseĀ(III) centers have either a square-pyramidal (<b>1</b> and <b>3</b>) or an octahedral (<b>2</b> and <b>5</b>) geometry, made up of a Salen-type tetradentate ligand (H<sub>2</sub>L) as established by X-ray diffraction analysis. The VāOāMn
bridge angle in these compounds varies systematically from 155.3Ā°
to 128.1Ā° in going from <b>1</b> to <b>5</b> while
the corresponding dihedral angle between the basal planes around the
metal centers changes from 86.82Ā° to 20.92Ā°, respectively.
The VāOāFe-type complexes (<b>6</b> and <b>7</b>) are tetranuclear, in which the two dinuclear VĀ(Ī¼-O)ĀFe
units are connected together by apical ironĀ(III)āaryl oxide
interactions, forming a dimeric structure with a pair of FeāOāFe
bridges. The X-ray data also confirm the Vī»O ā M canonical
form to contribute predominantly on the overall VāOāM
bridge structure. The molecules in solution also retain their heterobinuclear
composition, as established by electrospray ionization mass spectrometry
and <sup>51</sup>V NMR spectroscopy. Electrochemically, these complexes
are quite interesting; the manganeseĀ(III) complexes (<b>1</b>ā<b>5</b>) display three successive reductions (processes
IāIII), each with a monoelectron stoichiometry. Process I is
due to a Mn<sup>III</sup>/Mn<sup>II</sup> reduction (<i>E</i><sub>1/2</sub> ranges between ā0.32 and ā0.05 V), process
II is a ligand-based reduction, and process III (<i>E</i><sub>1/2</sub> = ā¼1.80 V) owes its origin to a V<sup>V</sup>O/V<sup>IV</sup>O reduction; all potentials are versus Ag/AgCl. The
ironĀ(III) compounds (<b>6</b> and <b>7</b>), on the other
hand, show at least four irreversible processes, appearing at <i>E</i><sub>pc</sub> = ā0.20, ā1.0, ā1.58,
and ā1.68 V in compound <b>6</b> (processes IVāVII),
together with a reversible process (process VIII) at <i>E</i><sub>1/2</sub> = ā1.80 V (Ī<i>E</i><sub>p</sub> = 80 mV). While the first two of these are due to Fe<sup>III</sup>/Fe<sup>II</sup> reductions at the two ironĀ(III) centers of these
tetranuclear cores, the reversible reduction at a more negative potential
(ca. ā1.80 V) is due to a V<sup>V</sup>O/V<sup>IV</sup>O-based
electron transfer
Homo- and Heterometal Complexes of OxidoāMetal Ions with a Triangular [V(V)OāMOāV(V)O] [M = V(IV) and Re(V)] Core: Reporting Mixed-Oxidation OxidoāVanadium(V/IV/V) Compounds with Valence Trapped Structures
A new
family of trinuclear homo- and heterometal complexes with
a triangular [VĀ(V)ĀOāMOāVĀ(V)ĀO] (M = VĀ(IV), <b>1</b> and <b>2</b>; ReĀ(V), <b>3</b>] all-oxidoāmetal
core have been synthesized following a single-pot protocol using compartmental
Schiff-base ligands, <i>N</i>,<i>N</i>ā²-bisĀ(3-hydroxysalicylidene)-diiminoalkanes/arene
(H<sub>4</sub>L<sup>1</sup>āH<sub>4</sub>L<sup>3</sup>). The
upper compartment of these ligands with N<sub>2</sub>O<sub>2</sub> donor combination (Salen-type) contains either a VĀ(IV) or a ReĀ(V)
center, while the lower compartment with O<sub>4</sub> donor set accommodates
two VĀ(V) centers, stabilized by a terminal and a couple of bridging
methoxido ligands. The compounds have been characterized by single-crystal
X-ray diffraction analyses, which reveal octahedral geometry for all
three metal centers in <b>1</b>ā<b>3</b>. Compound <b>1</b> crystallizes in a monoclinic space group <i>P</i>2<sub>1</sub>/<i>c</i>, while both <b>2</b> and <b>3</b> have more symmetric structures with orthorhombic space group <i>Pnma</i> that renders the vanadiumĀ(V) centers in these compounds
exactly identical. In DMF solution, compound <b>1</b> displays
an 8-line EPR at room temperature with āØ<i>g</i>ā©
and āØ<i>A</i>ā© values of 1.972 and 86.61 Ć
10<sup>ā4</sup> cm<sup>ā1</sup>, respectively. High-resolution
X-ray photoelectron spectrum (XPS) of this compound shows a couple
of bands at 515.14 and 522.14 eV due to vanadium 2p<sub>3/2</sub> and
2p<sub>1/2</sub> electrons in the oxidation states +5 and +4, respectively.
All of these, together with bond valence sum (BVS) calculation, confirm
the trapped-valence nature of mixed-oxidation in compounds <b>1</b> and <b>2</b>. Electrochemically, compound <b>1</b> undergoes
two one-electron oxidations at <i>E</i>
<sub>1/2</sub> =
0.52 and 0.83 V vs Ag/AgCl reference. While the former is due to a
metal-based VĀ(IV/V) oxidation, the latter one at higher potential
is most likely due to a ligand-based process involving one of the
catecholate centers. A larger cavity size in the upper compartment
of the ligand H<sub>4</sub>L<sup>3</sup> is spacious enough to accommodate
ReĀ(V) with larger size to generate a rare type of all-oxido heterotrimetallic
compound (<b>3</b>) as established by X-ray crystallography
Homo- and Heterometal Complexes of OxidoāMetal Ions with a Triangular [V(V)OāMOāV(V)O] [M = V(IV) and Re(V)] Core: Reporting Mixed-Oxidation OxidoāVanadium(V/IV/V) Compounds with Valence Trapped Structures
A new
family of trinuclear homo- and heterometal complexes with
a triangular [VĀ(V)ĀOāMOāVĀ(V)ĀO] (M = VĀ(IV), <b>1</b> and <b>2</b>; ReĀ(V), <b>3</b>] all-oxidoāmetal
core have been synthesized following a single-pot protocol using compartmental
Schiff-base ligands, <i>N</i>,<i>N</i>ā²-bisĀ(3-hydroxysalicylidene)-diiminoalkanes/arene
(H<sub>4</sub>L<sup>1</sup>āH<sub>4</sub>L<sup>3</sup>). The
upper compartment of these ligands with N<sub>2</sub>O<sub>2</sub> donor combination (Salen-type) contains either a VĀ(IV) or a ReĀ(V)
center, while the lower compartment with O<sub>4</sub> donor set accommodates
two VĀ(V) centers, stabilized by a terminal and a couple of bridging
methoxido ligands. The compounds have been characterized by single-crystal
X-ray diffraction analyses, which reveal octahedral geometry for all
three metal centers in <b>1</b>ā<b>3</b>. Compound <b>1</b> crystallizes in a monoclinic space group <i>P</i>2<sub>1</sub>/<i>c</i>, while both <b>2</b> and <b>3</b> have more symmetric structures with orthorhombic space group <i>Pnma</i> that renders the vanadiumĀ(V) centers in these compounds
exactly identical. In DMF solution, compound <b>1</b> displays
an 8-line EPR at room temperature with āØ<i>g</i>ā©
and āØ<i>A</i>ā© values of 1.972 and 86.61 Ć
10<sup>ā4</sup> cm<sup>ā1</sup>, respectively. High-resolution
X-ray photoelectron spectrum (XPS) of this compound shows a couple
of bands at 515.14 and 522.14 eV due to vanadium 2p<sub>3/2</sub> and
2p<sub>1/2</sub> electrons in the oxidation states +5 and +4, respectively.
All of these, together with bond valence sum (BVS) calculation, confirm
the trapped-valence nature of mixed-oxidation in compounds <b>1</b> and <b>2</b>. Electrochemically, compound <b>1</b> undergoes
two one-electron oxidations at <i>E</i>
<sub>1/2</sub> =
0.52 and 0.83 V vs Ag/AgCl reference. While the former is due to a
metal-based VĀ(IV/V) oxidation, the latter one at higher potential
is most likely due to a ligand-based process involving one of the
catecholate centers. A larger cavity size in the upper compartment
of the ligand H<sub>4</sub>L<sup>3</sup> is spacious enough to accommodate
ReĀ(V) with larger size to generate a rare type of all-oxido heterotrimetallic
compound (<b>3</b>) as established by X-ray crystallography
Ligand-Induced Tuning of the Oxidase Activity of Ī¼āHydroxidodimanganese(III) Complexes Using 3,5-Di-<i>tert</i>-butylcatechol as the Substrate: Isolation and Characterization of Products Involving an Oxidized Dioxolene Moiety
Oxidase activities
of a Ī¼-hydroxidodimanganeseĀ(III) system involving a series of
tetradentate capping ligands H<sub>2</sub>L<sup>R<sub>1</sub>,R<sub>2</sub></sup> with a pair of phenolate arms have been investigated
in the presence of 3,5-di-<i>tert</i>-butylcatechol (H<sub>2</sub>DBC) as a coligand cum-reductant. The reaction follows two
distinctly different paths, decided by the substituent combinations
(R<sub>1</sub> and R<sub>2</sub>) present in the capping ligand. With
the ligands H<sub>2</sub>L<sup><i>t</i>āBu,<i>t</i>āBu</sup> and H<sub>2</sub>L<sup><i>t</i>āBu,OMe</sup>, the products obtained are semiquinonato compounds
[Mn<sup>III</sup>(L<sup><i>t</i>āBu,<i>t</i>āBu</sup>)Ā(DBSQ)]Ā·2CH<sub>3</sub>OH (<b>1</b>)
and [Mn<sup>III</sup>(L<sup><i>t</i>āBu,OMe</sup>)Ā(DBSQ)]Ā·CH<sub>3</sub>OH (<b>2</b>), respectively. In
the process, molecular oxygen is reduced by two electrons to generate
H<sub>2</sub>O<sub>2</sub> in the solution, as confirmed by iodometric
detection. With the rest of the ligands, viz., H<sub>2</sub>L<sup>Me,Me</sup>, H<sub>2</sub>L<sup><i>t</i>āBu,Me</sup>, H<sub>2</sub>L<sup>Me,<i>t</i>āBu</sup>, and H<sub>2</sub>L<sup>Cl,Cl</sup>, the products initially obtained are believed
to be highly reactive quinonato compounds [Mn<sup>III</sup>(L<sup>R<sub>1</sub>,R<sub>2</sub></sup>)Ā(DBQ)]<sup>+</sup>, which undergo
a domino reaction with the solvent methanol to generate products of
composition [Mn<sup>III</sup>(L<sup>R<sub>1</sub>,R<sub>2</sub></sup>)Ā(BMOD)] (<b>3</b>ā<b>6</b>) involving a nonplanar
dioxolene moiety, viz., 3,5-di-<i>tert</i>-butyl-3-methoxy-6-oxocyclohexa-1,4-dienolate
(BMOD<sup>ā</sup>). This novel dioxolene derivative is formed
by a Michael-type nucleophilic 1,4-addition reaction of the methoxy
group to the coordinated quinone in [Mn<sup>III</sup>(L<sup>R<sub>1</sub>,R<sub>2</sub></sup>)Ā(DBQ)]<sup>+</sup>. During this reaction,
molecular oxygen is reduced by four electrons to generate water. The
products have been characterized by single-crystal X-ray diffraction
analysis as well as by spectroscopic methods and magnetic measurements.
Density functional theory calculations have been made to address the
observed influence of the secondary coordination sphere in tuning
the two-electron versus four-electron reduction of dioxygen. The semiquinone
form of the dioxolene moiety is stabilized in compounds <b>1</b> and <b>2</b> because of extended electron delocalization via
participation of the appropriate metal orbital(s)
Tetranuclear Hetero-Metal [Co<sup>II</sup><sub>2</sub>Ln<sup>III</sup><sub>2</sub>] (Ln = Gd, Tb, Dy, Ho, La) Complexes Involving Carboxylato Bridges in a Rare Ī¼<sub>4</sub>āĪ·<sup>2</sup>:Ī·<sup>2</sup> Mode: Synthesis, Crystal Structures, and Magnetic Properties
A new
family of 3dā4f heterometal 2 Ć 2 complexes [Co<sup>II</sup><sub>2</sub>(L)<sub>2</sub>(PhCOO)<sub>2</sub>Ln<sup>III</sup><sub>2</sub>(hfac)<sub>4</sub>] (<b>1</b>ā<b>5</b>)
(Ln = Gd (compound <b>1</b>), Tb (compound <b>2</b>),
Dy (compound <b>3</b>), Ho (compound <b>4</b>), and
La (compound <b>5</b>)) have been synthesized in moderate yields
(48ā63%) following a single-pot protocol using stoichiometric
amounts (1:1 mol ratio) of [Co<sup>II</sup>(H<sub>2</sub>L)Ā(PhCOO)<sub>2</sub>] (H<sub>2</sub>L = <i>N</i>,<i>N</i>ā²-dimethyl-<i>N</i>,<i>N</i>ā²-bisĀ(2-hydroxy-3,5-dimethylbenzyl)Āethylenediamine)
as a metalloligand and [Ln<sup>III</sup>(hfac)<sub>3</sub>(H<sub>2</sub>O)<sub>2</sub>] (Hhfac = hexafluoroacetylacetone) as a lanthanide
precursor compound. Also reported with this series is the ZnāDy
analog [Zn<sup>II</sup><sub>2</sub>(L)<sub>2</sub>(PhCOO)<sub>2</sub>Dy<sup>III</sup><sub>2</sub>(hfac)<sub>4</sub>] <b>6</b> to
help us in understanding the magnetic properties of these compounds.
The compounds <b>1</b>ā<b>6</b> are isostructural.
Both hexafluoroacetylacetonate and benzoate play crucial roles in
these structures as coligands in generating a tetranuclear core of
high thermodynamic stability through a self-assembly process. The
metal centers are arranged alternately at the four corners of this
rhombic core, and the carboxylato oxygen atoms of each benzoate moiety
bind all of the four metal centers of this core in a rare Ī¼<sub>4</sub>āĪ·<sup>2</sup>:Ī·<sup>2</sup> bridging mode
as confirmed by X-ray crystallography. The magnetic susceptibility
and magnetization data confirm a paramagnetic behavior, and no remnant
magnetization exists in any of these compounds at vanishing magnetic
field. The metal centers are coupled in an antiferromagnetic manner
in these compounds. The [Co<sup>II</sup><sub>2</sub>Dy<sup>III</sup><sub>2</sub>] compound exhibits a slow magnetic relaxation below
6 K, as proven by the AC susceptibility measurements; the activation
energy reads <i>U</i>/<i>k</i><sub>B</sub> = 8.8
K (Ļ<sub>0</sub> = 2.0 Ć 10<sup>ā7</sup> s) at <b>B</b><sub>DC</sub> = 0, and <i>U</i>/<i>k</i><sub>B</sub> = 7.8 K (Ļ<sub>0</sub> = 3.9 Ć 10<sup>ā7</sup> s) at <b>B</b><sub>DC</sub> = 0.1 T. The [Zn<sup>II</sup><sub>2</sub>Dy<sup>III</sup><sub>2</sub>] compound also behaves as a single-molecule
magnet with <i>U</i>/<i>k</i><sub>B</sub> = 47.9
K and Ļ<sub>0</sub> = 2.75 Ć 10<sup>ā7</sup> s
Pentanuclear 3dā4f Heterometal Complexes of M<sup>II</sup><sub>3</sub>Ln<sup>III</sup><sub>2</sub> (M = Ni, Cu, Zn and Ln = Nd, Gd, Tb) Combinations: Syntheses, Structures, Magnetism, and Photoluminescence Properties
A new family of pentanuclear 3dā4f
heterometal complexes of general composition [Ln<sup>III</sup><sub>2</sub>(M<sup>II</sup>L)<sub>3</sub>(Ī¼<sub>3</sub>-O)<sub>3</sub>H]Ā(ClO<sub>4</sub>)Ā·<i>x</i>H<sub>2</sub>O (<b>1</b>ā<b>5</b>) [Ln = Nd, M = Zn, <b>1</b>;
Nd, Ni, <b>2</b>; Nd, Cu, <b>3</b>; Gd, Cu, <b>4</b>; Tb, Cu, <b>5</b>] have been synthesized in moderate yields
(50ā60%) following a self-assembly reaction involving the hexadentate
phenol-based ligand, viz., <i>N</i>,<i>N</i>-bisĀ(2-hydroxy-3-methoxy-5-methylbenzyl)-<i>N</i><sup>ā²</sup>,<i>N</i><sup>ā²</sup>-diethylethylenediamine (H<sub>2</sub>L). Single-crystal X-ray diffraction
analyses have been used to characterize these complexes. The compounds
are all isostructural, having a 3-fold axis of symmetry that passes
through the 4f metal centers. The [M<sup>II</sup>L] units in these
complexes are acting as bis-bidentate metalloligands and, together
with Ī¼<sub>3</sub>-oxido bridging ligands, complete the slightly
distorted monocapped square antiprismatic nine-coordination environment
around the 4f metal centers. The cationic complexes also contain a
H<sup>+</sup> ion that occupies the central position at the 3-fold
axis. Magnetic properties of the copperĀ(II) complexes (<b>3</b>ā<b>5</b>) show a changeover from antiferromagnetic
in <b>3</b> to ferromagnetic 3dā4f interactions in <b>4</b> and <b>5</b>. For the isotropic Cu<sup>II</sup>āGd<sup>III</sup> compound <b>4</b>, the simulation of magnetic data
provides very weak CuāGd (<i>J</i><sub>1</sub> =
0.57 cm<sup>ā1</sup>) and GdāGd exchange constants (<i>J</i><sub>2</sub> = 0.14 cm<sup>ā1</sup>). Compound <b>4</b> is the only member of this triad, showing a tail of an out-of-phase
signal in the ac susceptibility measurement. A large-spin ground state
(<i>S</i> = 17/2) and a negative value of <i>D</i> (ā0.12 cm<sup>ā1</sup>) result in a very small barrier
(8 cm<sup>ā1</sup>) for this compound. Among the three Nd<sup>III</sup><sub>2</sub>M<sup>II</sup><sub>3</sub> (M = Zn<sup>II</sup>, Ni<sup>II</sup>, and Cu<sup>II</sup>) complexes, only the Zn<sup>II</sup> analogue (<b>1</b>) displays an NIR luminescence due
to the <sup>4</sup>F<sub>3/2</sub> ā <sup>4</sup>I<sub>11/2</sub> transition in Nd<sup>III</sup> when excited at 290 nm. The rest
of the compounds do not show such Nd<sup>III</sup>/Tb<sup>III</sup>-based emission. The paramagnetic Cu<sup>II</sup> and Ni<sup>II</sup> ions quench the fluorescence in <b>2</b>ā<b>5</b> and thereby lower the population of the triplet state
Dinuclear Iron(III) and Cobalt(III) Complexes Featuring a Biradical Bridge: Their Molecular Structures and Magnetic, Spectroscopic, and Redox Properties
Bis-bidentate ligand
H<sub>4</sub>L<sup><i>B</i></sup> featuring two <i>o</i>-amidophenol noninnocent units was used to synthesize novel
binuclear complexes [(L<sup><i>R</i></sup>)ĀM<sup>III</sup>(ā¢L<sup><i>B</i></sup>ā¢)ĀM<sup>III</sup>(L<sup><i>R</i></sup>)]Ā(ClO<sub>4</sub>)<sub>2</sub>, M = Fe (<b>1</b>) and Co (<b>2</b>, <b>3</b>), with HL<sup><i>R</i></sup> (R = CH<sub>3</sub>, Cl) being the facially coordinating
tetradentate coligands. Upon the synthesis, the fully reduced amidophenolate
form of the ligand (L<sup><i>B</i></sup>)<sup>4ā</sup> becomes oxidized, resulting in the formation of a rare example of
a biradical (ā¢L<sup><i>B</i></sup>ā¢)<sup>2ā</sup> bridge connecting two metal ions, as supported by X-ray crystallography.
The electronic structures of the complexes have been probed by MoĢssbauer
spectroscopy, magnetic susceptibility measurements, and electron paramagnetic
resonance (EPR) spectroscopy. Species <b>1</b> contains two
high-spin FeĀ(III) ions (<i>S</i> = 5/2) each coupled strongly
antiferromagnetically (|<i>J</i>| > 150 cm<sup>ā1</sup>; <b>HĢ</b> = ā<i>2J</i><b>SĢ</b><sub>1</sub><b>SĢ</b><sub>2</sub>) with a semiquinone
Ļ-radical (<i>S</i> = 1/2) form of the bridging (ā¢L<sup><i>B</i></sup>ā¢)<sup>2ā</sup> ligand. The
effective <i>S</i> = 2 spins of each [FeĀ(III)+R<sup>ā</sup>] monomeric unit are then weakly ferromagnetically coupled with <i>J</i> = +0.22 cm<sup>ā1</sup>. Species <b>2</b> and <b>3</b> reveal very similar electronic structures: the
low-spin CoĀ(III) ion is diamagnetic, which leaves the two-spin carriers
at the bridging (ā¢L<sup><i>B</i></sup>ā¢)<sup>2ā</sup> biradical to display an isotropic EPR signal at <i>g</i> = 1.995 for <b>2</b> (1.993 for <b>3</b>)
in solution at room temperature and in the frozen state with no hyperfine
structure. The weak half-field signal at <i>g</i> = 3.988
for <b>2</b> (3.978 for <b>3</b>) was also observed at
17 K for the spin-forbidden |Ī<i>M</i><sub>S</sub>| = 2 transition due to ferromagnetically coupled <i>S</i> = 1/2 spins (<i>J</i> = +47 cm<sup>ā1</sup>) of
the bridging biradical. The compounds show rich electrochemistry,
displaying two (<b>1</b>) or four (<b>2</b>, <b>3</b>) one-electron reversible processes. Normal and differential pulse
voltammetry as well as constant potential coulometry, combined with
EPR experiments, confirmed that the observed electron transfers are
all localized at the bridging noninnocent (ā¢L<sup><i>B</i></sup>ā¢)<sup>2ā</sup> ligand