Phosphazenes, cyclic or polymeric forms, are unique carriers for transition metals owing to their ability to serve as versatile multifunctional ligands and templates. The type of side group attached to the phosphazene chain and transition metals have a powerful effect on the physical and chemical characteristics. As object of our program to better understand the structure-property relationships in poly(organometallic phosphazenes), we have synthesized a series of small molecule cyclic phosphazenes as structural models for the corresponding high polymers.
The crystal structure of 1 shows that the six pyrazole groups are randomly oriented. The phosphazene ring is almost planar, with a maximum deviation of 0.034Å from the best plane. Reaction of 3 with three fold excess amount of $MX_n$ in $CH_2Cl_2$ gave unprecedented mononuclear metallophosphazenes [$LMX_n$] ($MX_n$ = $HgCl_2$ 6, $Mo(CO)_3$ 8), dinuclear metallophosphazenes [$X_nM(\mu-L)MX_n$] ($MX_n=ZnCl_2$ 4, CuI 5, $CuCl_2$ 9, $CoCl_2$ 10, $MnCl_2$ 11) or patially hydrolyzed metallophosphazene 7 ($MX_n$ = $FeCl_3$). In 4, L coordinates two $ZnCl_2$ units via geminal pyrazolyl $\eta^2-N_2$ core and via an $\eta^3-N_3$ bite, giving distorted tetrahedral(Td) and trigonalbipyramidal(TBP) geometries around zinc atoms, respectively. In 5, the ability of L to provide double tridentate $N_3$ cores involving phosphazene ring nitrogens affords two severely distorted tetrahedral Cu centers disposed on opposite sides of a rather planar phosphazene ring plane with a separation of 6.790(2)Å. In solution at ambient temperature, the compounds 4 and 5 lose their solid state symmetry of $C_1$ and $C_2$ respectively and undergo unique fluxional motions. The compound 4 shows unusual solvent dependency of fluxionality and in acetone, $A_2B$ phosphorus coupling pattern is seen at 188K while in dichloromethane, a very complicated spectral change results. At low temperature limit, the solution symmetry of 5 in $CD_2Cl_2$ approaches to that of solid state, giving rise to $A_2B$ phosphorus coupling pattern.
In 7, two phosphazene rings are connected via iron(III) and oxo groups, leading to a macro ring system of $C_{2h}$ molecular symmetry. Each iron center has a distorted octahedral geometry with $N_4OCl$ ligand sphere. The established composition of 7 implies that prior to the function of 7, the ligation and disproportion of $FeCl_3$ are followed by partial hydrolysis of pyrazole ring in phosphazene skeleton to yield the product.
In 8, the geometry around the metal is a distorted octahedral with longer Mo-N bonds on one face and shorter M-C bonds on the opposite face. The metal is -0.664Å from the mean plane mentioned above and it lies on the opposite side of the N1 atom.
In 9 and 11, the structures are rare example of a cyclotriphosphazene ring functioning as a bridging ligand system via two N3 cores between metal atoms. The coordination each metal is through two non-geminal pyrazolyl nitrogen atoms and one cyclophosphazene ring nitrogen atom. 9 and 10 have no significant intranucleus paramagnetic spin exchange coupling, respectively.
이 연구의 주된 목적은 피라졸릴포스파젠 리간드와 다양한 전이금속과의 반응을 통하여 새로운 유기금속 포스파젠 화합물을 합성하고 여러가지 분광학적인 방법을 통하여 characterization을 하며 X-ray diffraction method를 통하여 구조분석을 하는데 초점을 맞추었다. 모든 반응은 리간드와 금속이온의 비율을 1:3 으로 했음에도 불구하고 단핵 또는 이핵 착물을 형성하였고 금속이온은 두개의 non-geminal 피라졸 질소 그리고 한개의 포스파젠 고리질소와 배위를 하며 Zn(II)와 Co(II)착물의 경우에는 두개의 피라졸 질소만이 결합하는 Tetrahedral geometry 를 갖는 금속이온이 존재한다. Fe(II)착물의 경우에는 두개의 partially hydrolize 된 포스파젠 리간드가 Octahedral sphere 를 형성하고 있는 두개의 Fe(III)원자와 cyclic dimer system을 형성하고 있고 disproportion reaction에 의해서 $FeCl_4$ 음이온이 생성된다.
Zn(II)착물은 188K 에서 $^{31}P\{^1H\}$ NMR ($d_6$-acetone/acetone) 이 $A_2B$ type으로 coupling 하고 있으며 이것을 통하여 TBP 와 Td 가 연속적으로 변하는 Fluxional motion 을 하고 있음을 추측하였다. Cu(I)착물의 경우에도 218K 에서 $^{31}P\{^1H\}$ NMR ($CD_2Cl_2$)을 본결과 $A_2B$ type으로 coupling 하고 있으며 Td, Td가 연속적으로 변하는 Fluxional motion으로 추측된다. Cu(II)와 Co(II)착물들을 온도변화에 따른 magnetic susceptibility 를 측정해본 결과 두개의 paramagnetic 한 금속이온이 weak antiferromagnetic coupling 을 하고 있음을 알수 있었다.
