Phosphazenes ppt or pdf ( inorganic chemistry notes )

Phosphazenes

1. Phosphazenes Phosphonitrilic compounds
The Phosphazenes are cyclic or chain compounds that contain alternating
phosphorus and nitrogen atoms with two substituents on each phosphorus atom.
The three main structural types are cyclic trimer (Fig 1.2).cyelic tetramer (Fig 1.3)
and the oligomer or high polymer (Fig 1.4). A few cyellc pentamers and hexamers
are also known.
Neh
.-
2) -N=P-R
Ct-4)
C1-3)
Phosphonitilic polymers are a group of linear or cyclic compounds
containing.structural units of unsaturated-N =P-linkages. (a) Preparation:
The cyclic phosphonitrilic chlorides and their derivatives are the starting
materials for preparation ofvarious kinds of phosohonitrilic polymers

2. Phosphazenes (phosphonitrilic
compounds)
oN
in +3, P in +5
o Cyclic phosphazenes and polyphosphazenes
Phosphazenes refer to classes of organophosphorus compounds
featuring phosphorus(V) with a double bond between P and N. One
class of phosphazenes have the formula RN=P(NR2)3.These
phosphazenes are
also
known as
iminophosphoranes and
phosphine imides.They ae super bases.

3. Largest class of inorganic polymers because of case of side group modification.
R
Jn n> 15000
Backbone comprises alermate P and N aloms. Side groups (R) can be organic
inorganic or onganometallic. Method of synthesis allows modilication of side
groups.
Uses include sold electrolytes (batteries), advanced elastomers (elastic at
low
l is presdREure). Acrospace
and automobile applications because of resistance to
rbe

4. Drawing
Polyphosphazenes:
These contain more than two P N-groups.Polymeric
phosphazene dichlorides are formed when further halogen or
halophosphorus substitutions of NH groups in P takes place.
The polymeric phosphazene dichlorides can be represented as
PCL] PCL
These form chains and cyelic structures having 'n' value
upto 10'.
The simple representation of
polyphosphazene dichlorides is made as (NPCh. These are prepared as follows:
Solvent (a halo hydrocarbon)
nPCl+nNH,CI
[NPC+4n HC1
120-150c
Cyclic trimer, tetramer etc. are prepared by using different conditions. Separation is done
through fractionation. The cyclic trimer, cyclo -[NPC1) on heating at 150-300°C furnishes
is oreserelymeric products.
But heating at a higher temperature (350 360'C) causes cleavage and
is preseAeroknerization

5. PREPARATION
rgarhee
aNPC),
ad (NPO;4 Can be prepund
by the ammooalysis of PC
PCL+NH(NPCh + 9HCI
,4RCL
+ 4NH,NPChl+
12HC1
aDeeompounds
can be prepared by
the reactbon betwen PCly and NH,C in presence of
Cor by heating
PCl, with solid NH,CI at 145-160*c
cHC
CHG
NPC,
+ deliC
PCl + NHC
145-1680
PCly+ NH,CT) (NPCH),
+ 4nHC
Boch the above
reactions produce a
maxture of vanious phosphonitrilic chlorides, but under
anrold
conditons, high yields
of (NPCI;)},
and (NPCI},
can be obtained. These two compounds
an be seperated
from each
other by using
the fact that (NPCI;)h
suhimes in vacwum a S0PC aa
white crystalline
solid whereas (NPCJ,
does not do so under these conditions
The
fomation of (NPC;),
takes place through
the following steps
(a) NHC
PC NH, PaL
(Ammonium
hexachlornphosphate-an
urstable compound)
Deconposio HN. PCIh+3HCI
) NH,PCL
CeakensainNPClH,+ nHCI
(o nHN PC
(-nHCT)
IS
preseniin
ts
with SOC),
in PC, to pive (NPCl)h
IS presening sN,6SOC,+ 12PCl 4NPClh 105+30* 1

6. A EEr tet Dredon
AA Ea comet t Sutan ) Sape
Paagaoh
Dr
230-250C
PC NH, or NHC
E
NHR
NR
N
NHR
Can also functionalise the P-N precursor prior to polyerisation.

7. HO.
OH
et.09
C HO
OH
INPHO
NH
HO
OH
(NPC1 in acid soluion
is
toydrolysed
to H,PO, and NI
(6) Hydrotysis of (NPCC, in boiling waler is
rapiad and a stable prodact is obainod
HO OH
C
KHOH
a
RO OH
ONPC
HO
OH
KEYANI iS presenting

8. Properties and applications
o High thermal stability, properties can control by
changing substituents
Ultra hydrophobic, retard flame
Sealing agent for semiconductors
a Good elastomer,flexible even at low
temperature-resistant to chemicals-used in fuel
lines, gaskets, shock absorbers
etc.
presening

9. Cis and trans conformers exist and barrier to rotation about the P-N bond is
very small. However, the bonding in phosphazenes is still not well understood
although
theories have
bee
discussed since 1960.
Empirical observations:
Phosphazenes
do not exhibit alternating
bond
lengths
but the bond
length is much
less than a single P-N bond
(multiple bond character). This means
hypervalent
P.
C
Polyphonphanenes are
not
coloured
and do no conduct electricity that is
characteristic of extensive conjugation.
-framwrk
The problem is distrihution of the remaining valence electrons.
Original Dewar proposed that Phosphorus-Jd orbitals
are involved in bonding
to
Is presentingve PN.P "islands' where N 2p, overlap P 3d oebitals

10. Drawing Paragraph
Onguar Dcwa proposcu uar Tiospuorus-u OUaIs IC voivcu r oOuung w
give P-N-P islands' where N 2p, overlap P 3d orbitals
P
Rotation about P-N bond is low energy because N 2p, can retain overlap with 3d
orbitals on rotation.
More recent calculations suggest ionic bonding appears to be dominant.
NI is presenting

11. Nature of bonding in triphosphazenes
Bonding in phosphazenes is quite interesting
Diphosphazene contains one P=N and one P-N bonds both of
which are equivalent and the bond length is shorter than single bond.
This is easily explained by resonance
In case of turimer and higher phosphazenes however things are complex.
At first
sight. there seems
to
be
alternate single and double bond conjugate
systems through out P-N-P
skeleton.
Such conjugate systems are expected to lead to delocalization of the
sort of
benzene.
The
cyelic trimer has an
accurately planar 6-membered ring
structure but.
unlike aromatic systems, it is dificult to reduce it electraochemically
Also, the spectral evidence of delocalized system (bathochromic ultraviolet
shift) is not found.This is explained by the unique and interesting structure
Jl is presteRTnighosphazenes
possess.

12. As in other phosphazenes, triphosphazenes have
)Very stable ring
i)All the
skeletal
interatomic distances are equal
if all the six
substituentgroups
on phosphorus
are identical.
i)A shorter
P-N bond length (-158 pm)
than single bond
-177 pm)
Civ)All the nitrogen atoms weakly basic hence protonable (more so
if substituents on Pare electron releasing).
The symmetry of the molecule is like that of benzene.
It has planar structure with three nitrogen and three phosphorus
atoms situated on alternate corners of the hexagon.
The substitutents (X)
on Pare placed above and below the plane.
If all the substituents
are identical then
three of them form
together one plane above and three form one plane below the
molecular plane.

13. Some more
features
are mentioned
below: Nitrogen
atoms are sp2 hybridized
hybridization
Two such hybrid orbitals are involved in d-DOObonding
Similarly.each phosphorus is sp3 hybridized
Three such hybrld orbitals are involved in a0-bonding
There is then one'in plane' n-bonding invoving the lone pair of N (sp2
orbital)
in
x plane and the vacant dxy
or dx2 -y2 orbital of the P-atom.
There are two 'out of plane' interactions:(0Heteromorphis interactions:
The singly occupied pzl
orbital on the
nitrogen overlaps
with the dxzo or
dyzO orbital of phosphorus (pm-dr bonding).

14. .oo
hape Fa
Fort Paragaah Daeng
Homomorphic interactions: There is a pT-pT
interaction of pz orbitals of two nitrogens through
the dyz orbital of the phosphorus in between.
t
is
believed
that
the two
contributions viz. heteromorphic and
homomorphic are dqual.
This
results in separation
of the UnDorbitals into localized 3
centre orbital islands.
There are 3 such islands with
interruptions
at the three
phosphorus atoms.These interruptions
in the M.O's.prevent the
systems from exhibiting delocalizationof the m-electron.
ing

15. 2
hnd
hape y
Fart Pragaah Dr
ig 11.12 Try af C
phonphance tal m
etim f iNi m
9
Carids, DEChpe
n, Elsevir Anid
P35 Repndnd wi
OMI NOTES PRO 1
SERting

16. hae
4LL0
A
coment to Smata e thed
Font Paragoh
sals in de-localization over selected thre-atom segments
of the ring,
but nodes ae
g 1 Sincture of trimeric phosphazene, PN,CI; (a) contributing
resonance structu
asenting

17. b)
DR. KARTHIKEYANLis presenting