PMID- 17335275
OWN - NLM
STAT- PubMed-not-MEDLINE
DCOM- 20070531
LR  - 20070326
IS  - 0020-1669 (Print)
IS  - 0020-1669 (Linking)
VI  - 46
IP  - 7
DP  - 2007 Apr 2
TI  - Conformational flexibility in 2,2'-Dioxybiphenyl-chloro-cyclotetraphosphazenes 
      and its relevance to polyphosphazene analogues.
PG  - 2575-83
AB  - The reaction of the cyclotetraphosphazene, [N4P4Cl8], with the difunctional 
      reagent, 2,2'-biphenol, in the presence of potassium carbonate in acetone 
      produced the spiro-substituted derivatives, 
      2,2'-dioxybiphenylhexachlorocyclotetraphosphazene, 
      bis(2,2'-dioxybiphenyl)tetrachloro-cyclotetraphosphazene, and 
      tris(2,2'-dioxybiphenyl)dichlorocyclotetraphosphazene. Both cis and trans 
      geometrical isomers of the bis compound are observed. Although chromatographic 
      separation of these was unsuccessful, a sample of the trans isomer was obtained 
      by fractional crystallization. The compounds all show non-first-order 31P NMR 
      spectra which were simulated to extract the spectral parameters. Single-crystal 
      X-ray structures of both the trans bis and the tris compounds show that the 
      cyclophosphazene rings exhibit conformational flexibility which gives rise to 
      different crystalline forms being obtained from the same solvent systems. 
      Crystals of trans-bis(2,2'-dioxybiphenyl)tetrachloro-cyclotetraphosphazene were 
      obtained in two different space groups: Pnna (orthorhombic) and P21/n 
      (monoclinic). In the orthorhombic structure, the dominant (72%) conformation of 
      one phosphazene ring is a chair form, and the other (28%) resembles a boat. While 
      for the monoclinic structure, the ring is virtually flat with an oval shape. In 
      both cases the dioxybiphenyl groups are found in R and S configurations in the 
      same molecule and are pi stacked in columns (Pnna) or involved in pi-pi or pi-H 
      interactions (P21/n), thus anchoring the phosphorus atoms of the 
      cyclotetraphosphazenes but still allowing flexibility in the ring conformations. 
      Three crystalline modifications of 
      tris(2,2'-dioxybiphenyl)dichloro-cyclotetraphosphazene were obtained: two in 
      space group P (triclinic), which contained two molecules of dichloromethane in 
      the unit cell, and one solvent-free form in space group P21/n (monoclinic). The 
      cyclophosphazene rings exhibit puckered conformations with the 
      trans-dioxybiphenyl moieties having opposing RS or SR conformations. DFT 
      calculations were carried out on each of the phosphazene ring conformations in 
      trans-bis(2,2'-dioxybiphenyl)tetrachlorocyclotetraphosphazene identified from the 
      X-ray diffraction analysis. It is concluded that intermolecular interactions 
      (i.e., pi-pi or pi-H) between the dioxybiphenyl groups is a factor that modifies 
      the nature of the potential energy surface between the different conformers. The 
      flexibility of the phosphazene ring is supported computationally through the 
      calculated low-energy barriers and experimentally through the highly disordered 
      phosphazene ring conformations observed in the solid state. The results on 
      2,2'-dioxybiphenyl-substituted cyclotetraphosphazenes provide evidence that 
      microcrystalline domains in their 2,2'-dioxybiphenyl-substituted polyphosphazene 
      analogues will be generated by similar pi-pi and pi-H interactions.
FAU - Ainscough, Eric W
AU  - Ainscough EW
AD  - Chemistry-Institute of Fundamental Sciences, Massey University, Private Bag 11 
      222, Palmerston North, New Zealand. e.ainscough@massey.ac.nz
FAU - Brodie, Andrew M
AU  - Brodie AM
FAU - Chaplin, Adrian B
AU  - Chaplin AB
FAU - Derwahl, Andreas
AU  - Derwahl A
FAU - Harrison, John A
AU  - Harrison JA
FAU - Otter, Carl A
AU  - Otter CA
LA  - eng
PT  - Journal Article
DEP - 20070303
PL  - United States
TA  - Inorg Chem
JT  - Inorganic chemistry
JID - 0366543
EDAT- 2007/03/06 09:00
MHDA- 2007/03/06 09:01
CRDT- 2007/03/06 09:00
PHST- 2007/03/06 09:00 [pubmed]
PHST- 2007/03/06 09:01 [medline]
PHST- 2007/03/06 09:00 [entrez]
AID - 10.1021/ic062141t [doi]
PST - ppublish
SO  - Inorg Chem. 2007 Apr 2;46(7):2575-83. doi: 10.1021/ic062141t. Epub 2007 Mar 3.