3 research outputs found
A Nonheme Iron(III) Superoxide Complex Leads to Sulfur Oxygenation
A new alkylthiolate-ligated nonheme iron complex, FeII(BNPAMe2S)Br (1), is reported. Reaction
of 1 with O2 at −40 °C, or reaction
of
the ferric form with O2•– at −80
°C, gives a rare iron(III)-superoxide intermediate, [FeIII(O2)(BNPAMe2S)]+ (2), characterized by UV–vis, 57Fe Mössbauer,
ATR-FTIR, EPR, and CSIMS. Metastable 2 then converts
to an S-oxygenated FeII(sulfinate) product via a sequential
O atom transfer mechanism involving an iron-sulfenate intermediate.
These results provide evidence for the feasibility of proposed intermediates
in thiol dioxygenases
Controlling Spin Crossover in a Family of Dinuclear Fe(III) Complexes via the Bis(catecholate) Bridging Ligand
Spin
crossover (SCO) complexes can reversibly switch between low
spin (LS) and high spin (HS) states, affording possible applications
in sensing, displays, and molecular electronics. Dinuclear SCO complexes
with access to [LS–LS], [LS–HS], and [HS–HS]
states may offer increased levels of functionality. The nature of
the SCO interconversion in dinuclear complexes is influenced by the
local electronic environment. We report the synthesis and characterization
of [{FeIII(tpa)}2spiro](PF6)2 (1), [{FeIII(tpa)}2Br4spiro](PF6)2 (2), and [{FeIII(tpa)}2thea](PF6)2 (3) (tpa = tris(2-pyridylmethyl)amine, spiroH4 =
3,3,3′,3′-tetramethyl-1,1′-spirobi(indan)-5,5′,6,6′-tetraol,
Br4spiroH4 = 3,3,3′,3′-tetramethyl-1,1′-spirobi(indan)-4,4′,7,7′-tetrabromo-5,5′,6,6′-tetraol,
theaH4 = 2,3,6,7-tetrahydroxy-9,10-dimethyl-9,10-dihydro-9,10-ethanoanthracene),
utilizing non-conjugated bis(catecholate) bridging ligands. In the
solid state, magnetic and structural analysis shows that 1 remains in the [HS–HS] state, while 2 and 3 undergo a partial SCO interconversion upon cooling from
room temperature involving the mixed [LS–HS] state. In solution,
all complexes undergo SCO from [HS–HS] at room temperature,
via [LS–HS] to mixtures including [LS–LS] at 77 K, with
the extent of SCO increasing in the order 1 2 3. Gas phase density functional theory
calculations suggest a [LS–LS] ground state for all complexes,
with the [LS–HS] and [HS–HS] states successively destabilized.
The relative energy separations indicate that ligand field strength
increases following spiro4– 4spiro4– 4–, consistent with solid-state
magnetic and EPR behavior. All three complexes show stabilization
of the [LS–HS] state in relation to the midpoint energy between
[LS–LS] and [HS–HS]. The relative stability of the [LS–HS]
state increases with increasing ligand field strength of the bis(catecholate)
bridging ligand in the order 1 2 3. The bromo substituents of Br4spiro4– increase the ligand field strength relative to spiro4–, while the stronger ligand field provided by thea4– arises from extension of the overlapping π-orbital system
across the two catecholate units. This study highlights how SCO behavior
in dinuclear complexes can be modulated by the bridging ligand, providing
useful insights for the design of molecules that can be interconverted
between more than two states
Controlling Spin Crossover in a Family of Dinuclear Fe(III) Complexes via the Bis(catecholate) Bridging Ligand
Spin
crossover (SCO) complexes can reversibly switch between low
spin (LS) and high spin (HS) states, affording possible applications
in sensing, displays, and molecular electronics. Dinuclear SCO complexes
with access to [LS–LS], [LS–HS], and [HS–HS]
states may offer increased levels of functionality. The nature of
the SCO interconversion in dinuclear complexes is influenced by the
local electronic environment. We report the synthesis and characterization
of [{FeIII(tpa)}2spiro](PF6)2 (1), [{FeIII(tpa)}2Br4spiro](PF6)2 (2), and [{FeIII(tpa)}2thea](PF6)2 (3) (tpa = tris(2-pyridylmethyl)amine, spiroH4 =
3,3,3′,3′-tetramethyl-1,1′-spirobi(indan)-5,5′,6,6′-tetraol,
Br4spiroH4 = 3,3,3′,3′-tetramethyl-1,1′-spirobi(indan)-4,4′,7,7′-tetrabromo-5,5′,6,6′-tetraol,
theaH4 = 2,3,6,7-tetrahydroxy-9,10-dimethyl-9,10-dihydro-9,10-ethanoanthracene),
utilizing non-conjugated bis(catecholate) bridging ligands. In the
solid state, magnetic and structural analysis shows that 1 remains in the [HS–HS] state, while 2 and 3 undergo a partial SCO interconversion upon cooling from
room temperature involving the mixed [LS–HS] state. In solution,
all complexes undergo SCO from [HS–HS] at room temperature,
via [LS–HS] to mixtures including [LS–LS] at 77 K, with
the extent of SCO increasing in the order 1 2 3. Gas phase density functional theory
calculations suggest a [LS–LS] ground state for all complexes,
with the [LS–HS] and [HS–HS] states successively destabilized.
The relative energy separations indicate that ligand field strength
increases following spiro4– 4spiro4– 4–, consistent with solid-state
magnetic and EPR behavior. All three complexes show stabilization
of the [LS–HS] state in relation to the midpoint energy between
[LS–LS] and [HS–HS]. The relative stability of the [LS–HS]
state increases with increasing ligand field strength of the bis(catecholate)
bridging ligand in the order 1 2 3. The bromo substituents of Br4spiro4– increase the ligand field strength relative to spiro4–, while the stronger ligand field provided by thea4– arises from extension of the overlapping π-orbital system
across the two catecholate units. This study highlights how SCO behavior
in dinuclear complexes can be modulated by the bridging ligand, providing
useful insights for the design of molecules that can be interconverted
between more than two states