Structural, electrochemical, ESR, an
d H
2O
2 reactivity stu
dies are reporte
d for [Mn(
dmptacn)Cl]ClO
4 (
1,
dmptacn= 1,4-bis(2-pyri
dylmethyl)-1,4,7-triazacyclononane) an
d binuclear complexes of bis(penta
dentate) ligan
ds, generate
dby attaching 2-pyri
dylmethyl arms to each secon
dary nitrogen in bis(1,4,7-triazacyclononane) macrocycles an
dlinke
d by ethyl (tmp
dtne, [Mn
2(tmp
dtne)Cl
2](ClO
4)
2·2DMF,
2), propyl (tmp
dtnp, [Mn
2(tmp
dtnp)Cl
2](ClO
4)
2·3H
2O,
3), butyl (tmp
dtnb, [Mn
2(tmp
dtnb)Cl
2](ClO
4)
2·DMF·2H
2O,
4),
m-xylyl (tmp
dtn-
m-X, [Mn
2(tmp
dtn-
m-X)Cl
2](ClO
4)
2,
5) an
d 2-propanol (tmp
dtnp-OH, [Mn
2(tmp
dtnp-OH)Cl
2](ClO
4)
2,
6) groups.
1 crystallizes in theorthorhombic space group
P2
12
12
1 (No. 19) with
a = 7.959(7) Å,
b = 12.30(1) Å, an
d c = 21.72(2) Å;
2, in themonoclinic space group
P2
1/
c (No. 14) with
a = 11.455(4) Å,
b = 15.037(6) Å,
c = 15.887(4) Å, an
d ddle"> =96.48(2)
deg.gif">;
3, in the monoclinic space group
P2
1/
c (No. 14) with
a = 13.334(2) Å,
b = 19.926(2) Å,
c = 18.799(1) Å, an
d ddle"> = 104.328(8)
deg.gif">; an
d [Mn
2(tmp
dtnb)Cl
2](ClO
4)
2·4DMF·3H
2O (
4'), in the monoclinic space group
P2
1/
n (No. 14) with
a = 13.361(3) Å,
b = 16.807(5) Å,
c = 14.339(4) Å, an
d ddle"> = 111.14(2)
deg.gif">. Significant
distortion of the Mn(II) geometry is evi
dent from the angle subten
de
d by the five-membere
d chelate (ca. 75
deg.gif">) an
dthe angles spanne
d by trans
donor atoms (<160
deg.gif">). The Mn geometry is interme
diate between octahe
dral an
dtrigonal prismatic, an
d for complexes
2-4, there is a systematic increase in M···M
distance with the length ofthe alkyl chain. Cyclic an
d square-wave voltammetric stu
dies in
dicate that
1 un
dergoes a 1e
- oxi
dation fromMn(II) to Mn(III) followe
d by a further oxi
dation to Mn
IV at a significantly more positive potential. The binuclearMn(II) complexes
2-5 are oxi
dize
d to the Mn(III) state in two unresolve
d 1e
- processes {Mn
II2 Mn
IIMn
III Mn
III2} an
d then to the Mn
IV state {Mn
III2 Mn
IIIMn
IV Mn
IV2}. For
2, the secon
d oxi
dation process waspartially resolve
d into two 1e
- oxi
dation processes un
der the con
ditions of square-wave voltammetry. In the caseof
6, initial oxi
dation to the Mn
III2 state occurs in two overlapping 1e
- processes as was foun
d for
2-5, but thiscomplex then un
dergoes two further clearly separate
d 1e
- oxi
dation processes to the Mn
IIIMn
IV state at +0.89 Van
d the Mn
IV2 state at +1.33 V (vs Fc/Fc
+). This behavior is attribute
d to formation of an alkoxo-bri
dge
d complex.Complexes
1-6 were foun
d to catalyze the
disproportionation of H
2O
2. A
ddition of H
2O
2 to
2 generate
d anoxo-bri
dge
d mixe
d-valent Mn
IIIMn
IV interme
diate with a characteristic 16-line ESR signal.