二吡啶胺配基的直線型鎳與鈀/鉑三核異金屬串 錯合物之合成與研究

Abstract

本研究以二吡啶胺配基( dipyridylamino ligand )為橋接配基，簡稱 Hdpa ，與金屬鎳鈀/鎳鉑合成對稱型三核異金屬串錯合物， 並經由NMR、ESI質譜鑑定成功得到預期產物[NiPdNi(dpa)4(X)2] (X=Cl、NCS)與[NiPtNi(dpa)4Cl2]，並對其做結構分析、磁性與電化學之探討。 由X-ray單晶繞射解析，錯合物皆為單斜晶系，[NiPdNi(dpa)4Cl2]和NiPtNi(dpa)4Cl2]空間群同屬為P21/c；[NiPdNi(dpa)4(NCS)2]為P2/c。主結構與一般三核鎳金屬串錯合物[Ni3(dpa)4X2] (X軸向配基)相同，四個三牙基(dpa - )都以全順向式(all syn form)的配位構型螺旋環繞兩個鎳金屬和一個鈀或鉑金屬離子而構成三個金屬直線型排列。金屬離子之間並無鍵結，因此兩端鎳離子的配位環境皆為五配位四角錐體，而中間的金屬離子為四配位平面四邊形，由於金屬離子配位型式的不同，造成金屬離子電子自旋組態的不同，因此配基上的氮與金屬鍵長也有差異(Pd-N(amido)≒2.00 A, Ni-N(py)≒2.12 A)、(Pt-N(amido)≒2.022 A, Ni-N(py)≒2.13 A)。 據X-ray晶體結構鑑定分析可推測鎳鈀及鎳鉑三核異金屬串錯合物共有兩種自旋態，中間正二價的金屬離子為低自旋(S = 0) d8電子組態，兩端鎳正二價離子為高自旋(S = 1) d8 電子組態。以超導量子干涉儀量測磁性，隨著溫度上升，錯合物[NiPdNi(dpa)4Cl2]的μeff從4 K的0.16 μB上升至300 K的2.35 μB；錯合物[NiPdNi(dpa)4(NCS)2]從0.14 μB，上升至2.21 μB；錯合物[NiPtNi(dpa)4Cl2] 在4 K低溫時為0.30 μB，隨著溫度上升至室溫(300 K)時為1.52 μB，可知錯合物皆為典型的反鐵磁性(antiferromagnetic)。以χM做理論擬合後，與三核鎳金屬串錯合物比較，[NiPdNi(dpa)4Cl2]反鐵磁性最弱(J = -175.3 cm-1)；[Ni3(dpa)4Cl2]為中(J = -218.2 cm-1)；[NiPtNi(dpa)4Cl2]呈現較大的反鐵磁性(J = -298.0 cm-1)，此成因要同時考慮兩種耦合交換作用(exchange coupling)：經由金屬-金屬之dz2軌域重疊進行的直接交換作用；與涉及金屬-架橋配基N (dx2-y2-p)軌域的super exchange。。 電化學分析下，[NiPdNi(dpa)4Cl2]錯合物具有良好的可逆氧化還原的特性，並在氧化的部分有一對可逆的氧化還原對，進行 OTTLE測量，出現吸收峰變化，更由高回復率再次驗證具有好的氧化還原特性。

The syntheses, crystal structures, magnetic properties, CVs and OTTLE analysis of a series of new trinuclear symmetric heterometal string complexes stabilized by four dipyridylamide (dap) ligands, [NiPdNi(dpa)4X2] (X=Cl,NCS; dpa= the anion of dipyridylamino) and [NiPtNi(dpa)4Cl2] are reported. X-ray structural analyses show that compounds exhibit an approximate D4 symmetry and a linear metal framework, axial ligands are bonded to both side of Ni ion, and the outer Ni ions in square-pyramidal (NiL4X) environment, and the center Pd/Pt ions in square-planar environment. The trinuclear linear metal chain is helically wrapped by four all syn type ligands, the structural pattern observed in most M3(dpa)4X2 complexes. The magnetic susceptibility of [NiPdNi(dpa)4X2] complexes are interprted in terms of antiferromagnetic interaction (J = -175.3 cm-1 for X=Cl and J = -188.0 cm-1 for X=NCS within the framework of the Heisenberg) between the Ni(II) magnetic centers, relatively weaker than homotrinuclear complexes[Ni3(dpa)4X2] . The property is at variance of [NiPtNi(dpa)4Cl2], for which a relatively strong antiferromagnetic interaction (J = -298.0 cm-1). The results for the the decrease of the magnetic interaction from [Ni3(dpa)4Cl2] to [NiPdNi(dpa)4Cl2] and increase from [NiPdNi(dpa)4Cl2] to [NiPtNi(dpa)4Cl2] assign we should simultaneously consider the two main mechanisims of the exchange interaction, a spin polarized process along the metal dz2 and the super exchange involving the metal-N (dx2-y2-p) bond, since the electronic configuration of Ni(II) magnetic centers are d8 high spin, indicate both dz2 and dx2-y2 orbitals have unpair electron. In the CV analysis, the complex has a good reversible redox property and a pair of reversible redox couples in oxidation state, and show the vanishing of the absorption peak tested by OTTLE, also represent the good redox property once again verified by the high response rate .