Burkhardt Anja, Spielberg Eike T, Görls Helmar, Plass Winfried
Institut für Anorganische und Analytische Chemie, Friedrich-Schiller-Universität Jena, Carl-Zeiss-Promenade 10, 07745 Jena, Germany.
Inorg Chem. 2008 Apr 7;47(7):2485-93. doi: 10.1021/ic701777t. Epub 2008 Mar 4.
The sugar-modified Schiff base ligand benzyl 2-deoxy-2-salicylideneamino-alpha-D-glucopyranoside H 2L, prepared by condensation of salicylaldehyde and the monomeric chitosan analogue benzyl 2-deoxy-2-amino-alpha-D-glucopyranoside, reacts with copper(II) acetate to form a self-assembled, alkoxo-bridged tetranuclear homoleptic copper(II) complex [{Cu(L)}4] (4) with Cu4O4 heterocubane core. The chiral complex 4 crystallizes in the space group P2 12 12 1. The tetranuclear complex 4 is composed of two dinuclear {Cu(L)}2 entities linked by the four mu 3-bridging C-3 alkoxide oxygen atoms of the sugar backbone. The preorganization of the dimeric {Cu(L)}2 entities is enforced by strong hydrogen bonds between the phenolate oxygen atom and the C-4 hydroxy group of the two constituting chiral monomeric building blocks. Therefore the Cu4O4 core can be classified as a type I or 2 + 4 cubane. The chirality of the structure is confirmed by circular dichroism (CD) spectra, which reveal a significant dichroism associated with the copper centered transitions at around 600 nm. Temperature dependent magnetic susceptibility measurements indicate ferromagnetic exchange interactions in complex 4. Fitting of the experimental data with a two J model based on the 2 + 4 topology ( H = - J1(S1S3 + S2S4) - J2(S1 + S3)(S2 + S4)) leads to exchange coupling constants of J1 = 64 and J2 = 4 cm(-1). The observed ferromagnetic coupling can be attributed to the very small Cu-O-Cu bridging angles within the Cu2O2 core of the constituting dimeric entities, which are a result of the conformational requirements introduced by the sugar backbone. 4 is not only the first example of an alkoxo-bridged tetranuclear copper(II) complex with Cu4O4 core representing the 2 + 4 cubane class with ferromagnetic ground state but also a rare example for the class of molecules combining a ferromagnetic ground state with optical activity. The ferromagnetic S = 2 ground state of 4 is confirmed by magnetization measurements and ESR spectroscopy.
糖修饰的席夫碱配体苄基2-脱氧-2-亚水杨基氨基-α-D-吡喃葡萄糖苷H₂L由水杨醛与单体壳聚糖类似物苄基2-脱氧-2-氨基-α-D-吡喃葡萄糖苷缩合制备，它与醋酸铜(II)反应形成一种自组装的、具有Cu₄O₄异立方烷核心的烷氧基桥连四核同配铜(II)配合物[{Cu(L)}₄] (4)。手性配合物4在空间群P2₁2₁2₁中结晶。四核配合物4由两个双核{Cu(L)}₂实体组成，它们通过糖骨架的四个μ₃桥连C-3烷氧基氧原子相连。二聚体{Cu(L)}₂实体的预组织是由酚氧原子与两个构成手性单体结构单元的C-4羟基之间的强氢键所强制形成的。因此，Cu₄O₄核心可归类为I型或2 + 4立方烷。结构的手性通过圆二色性(CD)光谱得到证实，该光谱显示在600 nm左右与铜中心跃迁相关的显著二色性。变温磁化率测量表明配合物4中存在铁磁交换相互作用。基于2 + 4拓扑结构的双J模型(H = -J₁(S₁S₃ + S₂S₄) - J₂(S₁ + S₃)(S₂ + S₄))对实验数据进行拟合，得到交换耦合常数J₁ = 64和J₂ = 4 cm⁻¹。观察到的铁磁耦合可归因于构成二聚体实体的Cu₂O₂核心内非常小的Cu-O-Cu桥连角，这是糖骨架引入的构象要求的结果。4不仅是具有Cu₄O₄核心、代表具有铁磁基态的2 + 4立方烷类的烷氧基桥连四核铜(II)配合物的首个例子，也是将铁磁基态与光学活性相结合的分子类别的罕见例子。4的铁磁S = 2基态通过磁化测量和电子顺磁共振光谱得到证实。
