含八牙配位基之三銅(II)金屬錯合物

Abstract

本研究使用兩種不同的合成策略(Protocol 1: Middle to End 或 Protocol 2: End to End)成功合成出對稱及不對稱八牙配位基衍生物(octadentate ligands)，(L2H-6/7-(α)-x, L2H-6/7-(β)-x與L2H-6-(γ)；如下圖)。以過氯酸銅(Copper(II) perchlorate)為起始物與八牙配位基於甲醇中後反應可以得到深藍色三銅錯合物。

此類三銅錯合物利用紅外光共振光譜(IR)、紫外光-可見光光譜(UV-Vis)、電噴灑質譜儀(ESI-MS)、 超導量子干涉磁化儀(SQUID)、電子自旋共振光譜(ESR)、導電度測量(conductivity measurement)與原素分析(elemental analyses)確認其組成為[(CuII)3(L)¬(-OH)(ClO4)3(H2O)4] 並對於其物理性質加以研究。 超導量子干涉磁化儀測量的結果顯示，此類三銅錯合物在高溫的範圍有明顯的反鐵磁耦合現象(antiferromagnetic coupling)，而在低溫範圍則需要引入反對稱交換耦合現象(antisymmetric exchange coupling)來解釋特殊的磁性行為。 從陰離子交換實驗的結果可以發現，橋接在兩個二價銅離子間的氫氧根離子(bridge hydroxide)，在酸性的條件下可以很容易的被其他陰離子交換出來；從改變酸鹼值的實驗中我們可以得知此類三銅錯合物在酸性條件下會變得不穩定並進行去金屬化反應(demetallization process)，但在鹼性條件下，則會再度形成含有橋接氫氧根離子的三銅錯合物；分析反應溶液的紫外光可見光光譜資料(max與Abs)，可以推論此一去金屬化反應為一可逆過程且具有酸鹼值依賴特性。此外，在實驗所嘗試過的金屬交換條件之下，本研究所使用的八牙配位基相對於其他金屬離子(如：CrII(NO3)3、MnCl2、FeCl3、CoII(ClO4)2、CoIII(NH3)6Cl3、NiII(ClO4)2與ZnCl2)而言對於銅離子的抓取具有較高的選擇性。 除了上述的三銅錯合物之外，本實驗中亦合成了一系列的含胺基-吡啶(amino-pyridine)雙牙配位基的單銅錯合物。單晶結構顯示，此類單銅錯合物在銅金屬中心具有雙四角錐結構(square bipyramid)，兩個胺基-吡啶配位基以相互為反式(trans)的位向占據了赤道向(equatorial)位置，而兩個過氯酸根的氧原子則占據了兩個軸向(axial)位置。經由比對不同胺基-吡啶雙芽配位基衍生物電噴灑質譜儀的結果，我們發現此類單銅錯合物在溶液狀態時處於單銅與雙銅離子團的多平衡(multiequilibrium)系統之中。而超導量子干涉磁化儀與電子自旋共振光譜測量的結果顯示此單銅錯合物具有相似於一般單銅錯合物的物理性質(Curie常數：C = 0.42 cm3 mol-1 K、Weiss常數： = -0.08 K與g = 2.06)。

New derivatives of octadentate ligands (L2H-6/7-(α)-x, L2H-6/7-(β)-x and L2H-6-(γ); see Chart I) have been synthesized. Two synthetic strategies including Protocol 1: Middle to End or Protocol 2: End to End have been employed for symmetrical and unsymmetrical octadentate ligands synthesis, respectively. The reactions of octadentate ligands with Cu(ClO4)2 yield the corresponding trinuclear copper(II) complexes. Such complexes have been characterized by IR, UV-Vis spectroscopies, ESI-MS, SQUID, ESR, conductivity measurement and elemental analyses. The chemical formulae of a deep blue compound is identified as a tricopper(II) complex [(CuII)3(L)¬(-OH)(ClO4)3(H2O)4]. The temperature dependence of MT measurements for the trinuclear copper(II) complexes ([(CuII)3(L-6-()-1)] and [(CuII)3(L-6-()-1)]) show special magnetic properties of complexes. At high temperature region (300 K), the MT values of tricopper(II) complexes are lower than those expected for three uncoupled S = 1/2 spins, and they decrease steadily with decreasing temperature. This behavior in high temperature region clearly indicates that intratrimer antiferromagnetic coupling is operating. At low temperature region, the MT values of tricopper(II) complexes are lower than 0.4 cm3 mol-1 K. This behavior in low temperature region clearly suggests that antisymmetrical exchange coupling is operating at this tricopper(II) system. The fitting results for high temperature region show that g = 2.046 and 2.062, J = -96.2 cm-1 and -103.4 cm-1 and j = -176.4 cm-1 and -202.7 cm-1 for trinuclear copper(II) complexes [(CuII)3(L-6-()-1)] and [(CuII)3(L-6-()-1)], respectively. From the results of ESI-MS and UV-Vis spectra, in acidic condition, the bridge hydroxide ion between two copper(II) centers of trinuclear copper(II) complex can be replaced by another anions easily, and the trinuclear copper(II) complex will be demetallized. After neutralizing the reaction mixture of demetallization test by NaOH, the evidences of ESI-MS and UV-Vis spectra show that this demetallization process is reversible, and the max and absorbance of the reaction mixture is highly pH dependence. The results of some metal exchange tests indicate that the octadentate ligang have better affinity to Cu(II) ions than other metal ions (i.e. CrII(NO3)3, MnCl2, FeCl3, CoII(ClO4)2, CoIII(NH3)6Cl3, NiII(ClO4)2 and ZnCl2) in experimental conditions.

Mononuclear copper(II) complexes bearing two amino-pyridie bidentate ligands, also have been synthesized for comparison. In solid state, the crystal structure shows that the geometry of copper(II) center is square bipyramid, which is surrounded by two amino-pyridine bidentate ligands and two perchlorate anions. The four equatorial and two axial position of distorted octahedron copper(II) center are occupied by two amino-pyridines and two perchlorate anions, respectively. After comparing the ESI-MS spectra of different monocopper(II) complexes, these purple mononuclear copper(II) complexes show multiequilibrium with mono-, di- and tricopper(II) clusters in solution state. The magnetic property of mononuclear copper(II) complex follows the Curie-Weiss law with a Curie constant of C = 0.42 cm3 mol-1 K, which is in the expected range for an isolated Cu(II) ion, and a Weiss constant of = -0.08 K, which arise from the weak intermolecular antiferromagnetic interaction. Room temperature X-band EPR spectrum of [(CuII)3(L-6-()-1)] and [CuII(L-(a)-1)2] shows a transition centered at g = 2.07 and g = 2.06, respectively.