A series of new organometallic polymers of the type
{[M(dmb)2]Y}
n
(dmb =
1,8-diisocyano-p-menthane;
Y = BF4
-, NO3
-,
ClO4
-, M = Cu; Y =
BF4
-, PF6
-,
NO3
-,
CH3CO2
-,
ClO4
-; M = Ag) are reported.
These
materials have been characterized from single-crystal X-ray diffraction
(for {[Ag(dmb)2]Y}
n
;
Y = BF4
-,
NO3
-,
ClO4
-), X-ray powder diffraction (which
established the isostructurality between M = Cu and Ag and the
relative
crystallinity level), differential scanning calorimetry (DSC),
solid-state magic spinning angle and solution
13C-NMR,
and spin−lattice relaxation time measurements
(T
1, 13C-NMR). Three synthesis
methods were employed in order to
obtain highly crystalline, semicrystalline, and highly amorphous
{[Cu(dmb)2]BF4}
n
polymers. One polymer has
been successfully characterized from a light-scattering technique.
For the amorphous
{[Cu(dmb)2]BF4}
n
polymer,
the molecular weights averaged 160 000. The Ag polymers are found
to be rather crystalline and exhibit very low
solubility properties. Except for the
{[Ag(dmb)2]PF6}
n
and the highly crystalline
{[Cu(dmb)2]BF4}
n
materials, all
polymers exhibit glass transitions in the 37−96 °C (305−340 K)
range, even if the materials exhibit a very large
crystallinity level. The
{[M(dmb)2]Y}
n
organometallic materials (M = Cu, Ag; Y =
BF4
-, PF6
-,
NO3
-,
CH3CO2
-)
are also strongly luminescent in the visible range (400−600 nm) at 77
K, exhibiting polyexponential emission decay
traces (either in the solid state or in solutions). By comparison
with the emission properties of the non-polymeric
[M(CN-t-Bu)4](BF4) compounds
(M = Cu, Ag) as a model for a monomeric unit, the first and
short-lived component
of the emission decay traces (30−90% in relative intensity) is
associated with a higher-energy emission localized at
one M center within the polymer (“monomer-like emission”).
This is also confirmed by time-resolved emission
spectroscopy from the comparision with the emission maxima. The
other components in the polyexponential decays
are associated with lower-energy emissions that are only present in the
polymers. This phenomenon is associated
with an energy transfer metal-to-metal delocalized along the M chain
somewhat similar to the exciton phenomenon
known in organic solids. The depolarization of the emission light
confirms the phenomenon. From density functional
theory calculations, the lowest energy excited states have been
assigned as MLCT (metal-to-ligand charge transfer)
with the HOMO being the M centered d orbitals, and the LUMO being the
π* MO centered on the isocyanide
groups. X-ray data for
{[Ag(dmb)2]BF4}
n
:
space group P212121,
orthorhombic, a = 9.3273(18) Å, b =
13.685(2)
Å, c = 22.124(4) Å, V = 2824.0(9)
Å3, Z = 4, D
calc =
1.353 g/cm3, R = 0.068,
R
w = 0.073.
{[Ag(dmb)2]NO3·0.70H2O}
n
:
space group P21 /c, monoclinic,
a = 13.1746(14) Å, b = 9.7475(11)
Å, c = 23.207(3) Å, β =
105.15(1)°, V = 2876.5(6) Å3,
Z = 4, D
calc = 1.297
g/cm3, R = 0.051, R
w
= 0.048.
{[Ag(dmb)2]ClO4}
n
:
space
group P212121,
orthorhombic, a = 9.282(2) Å, b =
13.772(2)...
