This work deals with the synthesis and characterization of various estertin(Ⅳ) complexes involving mixed multidentate ligands for elucidation on the coordination chemistry of organotin(Ⅳ) compounds.
$CH_3OOCCH_2CH_2SnCl_3$ reacts with the dithiocarbamate(dtc) ligand in appropriate mole ratios to yield crystalline solid products $ROOCCH_2CH_2Sn(S_2CNMe_2)_xC1_{3-x}$ ($\underline{Ia}$: R=Me, x=1; Ib: R=Me, x=2; Ic: R=Me, x=3). $\underline{Ia}$ adopts a distorted octahedral geometry with the chelating dtc and ester group via intramolecular carbonyl oxygen-to-tin coordination. However, in Ib and Ic the intramolecular coordination of the carbonyl group is not allowed in order to accommodate two and three bidentate dtc ligands, respectively.
The reaction of $\underline{Ia}$ series with an equimolar $Na_2S$ yields dimeric sulfides $[CH_3OOCCH_2CH_2Sn(S_2CNR_2)S]_2$ ($\underline{Ⅱa}$: R=Me; Ⅱb: R=Et) involving a rare centrosymmetric $Sn_2S_2$ four-membered ring. In these complexes the dtc ligand acts as bidentate and each Sn atom is pentacoordinate with local geometry of a distorted trigonal bipyramid.
The reaction of $\underline{Ia}$ series with diptych ligands $Y(CH_2CH_2XNa)_2$ affords stannatrane products, $ROOCCH_2CH_2Sn(S_2CNMe_2)(XCH_2CH_2)_2Y$($\underline{Ⅲa}$: R=Me, X=S, Y=0; $\underline{Ⅲa-1}$: R=Et, X=S, Y=O; $\underline{Ⅲc}$: R=Me, X=S, Y=S; $\underline{Ⅲd}$: R=Me, X=O, Y=NMe; $\underline{Ⅲd-1}$: R=Et, X=O, Y=NMe). These complexes are regarded as the first hexacoordinate stannabicyclooctanes. For $\underline{Ⅲa}$, however, unusually unsymmetrical chelation of the dtc ligand (Sn-S(1), 3.093(1)A; Sn-S(2), 2.493(1)A) along with the endocyclic ring constrain resulted in a highly distorted octahedral arrangement.
Diestertin(Ⅳ) complexes $(CH_3OOCCH_2CH_2)_2Sn(Ch)C1$ ($\underline{Ⅳa}$: $Ch=Me_2NCS_2$- (dtc) ; $\underline{Ⅳb}$: Ch=bispyrazolylborate (bpb)) also have been synthesized. $\underline{Ⅳb}$ shows hexacoordinate tin atom with chelating bpb and one ester group via a carbonyl oxygen-to-tin coordination whereas $\underline{Ⅳa}$ pentacoordinate with only the dtc chelation. The reaction of $\underline{Ⅳa}$ with $Na_2S$ in the mole ratio of 2:1 migrates the ligands to yield the disproportionation products, $(CH_3OOCCH_2CH_2)_2Sn(S_2CNMe_2)_2$ and its counter part, whereas the reaction of $\underline{Ⅳb}$ with $Na_2S$ under the same condition does not afford the corresponding products.
$CH_3OOCCH_2CH_2Sn(tpb)X_2$ (tpb: trispyrazolylborate; $\underline{Va}$: X=Cl; $\underline{Vb}$: X=NCS) show each discrete molecule of a distorted octahedral tin atom with the facial tpb ligand, where the carbonyl group is released from the tin atom to accommodate the tridentate ligand.
Finally, new estertin chloride and its derivatives, $CH_3OOCCH_2CH(COOCH_3)CH_2Sn(L)X_2$ ($\underline{VIa}$:L=Cl, X=C1; $\underline{VIb}$: $L=S_2CNMe_2$, X=Cl; $\underline{VIc}$: L=tpb, X=C1; $\underline{VId}$: $L=S_2CNMe_2$, $X_2=S$) have been synthesized. $\underline{VIb}$ and $\underline{VIc}$ show hexacoordination of the central tin atom whereas $\underline{VId}$ pentacoordination both in the solid state and in solution. However, the coordination number of $\underline{VIa}$ changes from six in solid state to five in solution.
농약, PVC 안정제, 촉매 그리고 최근에는 항암효과를 나타내므로서 심지어 의약품 등 새로운 용도의 길이 계속 열리고 있는 유기주석화합물들에 대한 화학적, 분광학적 연구결과는 주석원자의 배위수가 매우 다양하다는 사실과 주석원자의 배위수가 생물활성과 깊은 관련이 있음을 보여주고 있으나, 유기주석화합물들의 배위화학에 대한 뚜렸한 근거를 제시하지는 못하고 있는 실정이다.
따라서 유기주석화합물들의 배위화학을 연구하기 위해 주석원자의 주위환경에 민감한 구조를 갖는 에스테르주석화합물을 근간으로 하는 여러자리 리간드들이 치환된 새로운 유기주석화합물들을 합성하여, 생성물들의 반응성과 함께 그 구조를 규명하였다. 이들 화합물들에 대한 계통적인 연구결과, 유기주석화합물들의 배위구조는 주석원자에 결합되어 있는 원자 또는 원자단의 입체요인보다 전자요인이 더 중요하다는 사실을 보여주고 있다. 이러한 주석원자의 배위성질에 대한 강한 전자효과는 주족 금속원소의 특징인 에너지적으로 다소 높은 비어있는 d-궤도함수를 이용하기가 어렵기 때문일 것으로 판단된다. 한편, 이 연구결과는 7배위 유기주석화합물은 적절한 전자요인과 함께 전형적으로 작은 물기각도(bite angle) (70°이하) 의 리간드들을 갖는 경우에만 가능하다는 사실을 시사하고 있다.
