Abstract
The correlation was investigated between the observed heat of ligation and calculated quantum chemical quantities for octahedral $[M(H_2O)_{6-x}(NH_3)_x]^{2+} (M=Fe(II),\;Ni(II))$ complexes by EHMO(Extended Huckel Molecular Orbital) and ZINDO/1(Zerner's Intermediate Neglected of Differential Overlap)method. The net charge of $Fe^{2+}$ and $Ni^{2+}$ ion of octahedral $[M(H_2O)_{6-x}(NH_3)_x]^{2+}(M=Fe(II),\;Ni(II))$ complexes(x=O, 1, …, 6) decreased with substituting $NH_3$ for $H_2O$ molecules. It has found that a good correlation exists between the observed heat of ligation and the calculated quantum chemical quantities such as net charge of central atom, enthalpy of formation, and total dissociation energy. From this finding, we have obtained the following semiempirical linear equation ${\Delta}H_{obs}=-0.2858_{qFe}+0.8813(r=0.97),\;{\Delta}H_{obs}=-0.8981_{qNi}+1.7929(r=0.95),\;{\Delta}H_{obs}=-0.0031H_{f(Fe)}+0.5725(r=0.97),\;{\Delta}H_{obs}=-0.0095H_{f(Ni)}+0.9193(r=0.97),\;{\Delta}H_{obs}=0.0476E_{diss(Fe)}+0.6434(r=0.94),\;{\Delta}H_{obs}=0.1401E_{diss(Ni)}+1.1393(r=0.93)$.
Fe(II) 및 Ni(II) 이온에 $NH_3$ 리간드를 배위시켜 분자역학(MM2)법으로 최소에너지를 갖는 구조를 구한 후 확장분자궤도함수(EHMO)법 및 ZINDO/1법으로 양자화학적 양을 얻어 실험적 사실과 비교 검토하였다. 즉, 팔면체인 $[M(H_2O)_{6-x}(NH_3)_x]^{2+}(M=Fe(II),\;Ni(II)(x=0,\;1,\;…,\;6)에서 $NH_3$ 분자가 $H_2O$ 분자와 단계적으로 치환될 때에 따른 실측리간드화열이 MO 이론으로 계산한 팔면체형인 Fe(II)및 Ni(II)착물의 양자화학적 양인 중심금속의 알짜전하, 형성엔탈피, 총결합에너지로부터 실측 리간드화열$({\Delta}H_{obs})$을 이론적으로 예측할 수 있는 ${\Delta}H_{obs}=-0.2858_{qFe}+0.8813(r=0.97),\;{\Delta}H_{obs}=-0.8981_{qNi}+1.7929(r=0.95),\;{\Delta}H_{obs}=-0.0031H_{f(Fe)}+0.5725(r=0.97),\;{\Delta}H_{obs}=-0.0095H_{f(Ni)}+0.9193(r=0.97),\;{\Delta}H_{obs}=0.0476E_{diss(Fe)}+0.6434(r=0.94),\;{\Delta}H_{obs}=0.1401E_{diss(Ni)}+1.1393(r=0.93)$인 이론식을 각각 얻었다.