Rational Assembly of Soluble Copper(II) Phosphonates: Synthesis, Structure and Magnetism of Molecular Tetranuclear Copper(II) Phosphonates

The reactions of the dinuclear copper complexes [Cu2(L)(OAc)] [H3L = N,N′-(2-hydroxypropane-1,3-diyl)bis(salicylaldimine) or [Cu2(L′)(OAc)] (H3L′ = N,N′-(2-hydroxypropane-1,3-diyl)bis(4,5-dimethylsalicylaldimine)] with various phosphonic acids, RPO3H2 (R= t-Bu, Ph, c-C5H9, c-C6H11 or 2,4,6-i-Pr3-C6H2), leads to the replacement of the acetate bridge affording tetranuclear copper(II) phosphonates, [Cu4(L)2(t-BuPO3)](CH3OH)2(C6H6) (1), [Cu4(L)2(PhPO3)(H2O)2(NMe2CHO)](H2O)2 (2), [Cu4(L′)2(C5H9PO3)](CH3OH)2 (3), [Cu4(L′)2(C6H11PO3](MeOH)4(H2O)2 (4) and [Cu4(L′)2(C30H46P2O5)](PhCH3) (5). The molecular structures of 1−4 reveal that a [RPO3]2− ligand is involved in holding the four copper atoms together by a 4.211 coordination mode. In 5, an in situ formed [(RPO2)2O]4− ligand bridges two pairs of the dinuclear subunits. Magnetic studies on these complexes reveal that the phosphonate ligand is an effective conduit for magnetic interaction among the four copper centers present; a predominantly antiferromagnetic interaction is observed at low temperatures.

双核铜配合物[Cu₂(L)(OAc)]（其中H₃L = N,N′-(2-羟基丙烷-1,3-二基)双(水杨醛亚胺)）与[Cu₂(L′)(OAc)]（其中H₃L′ = N,N′-(2-羟基丙烷-1,3-二基)双(4,5-二甲基水杨醛亚胺)）可与各类膦酸RPO₃H₂（R = 叔丁基(t-Bu)、苯基(Ph)、环戊基(c-C₅H₉)、环己基(c-C₆H₁₁)或2,4,6-三异丙基苯基(2,4,6-i-Pr₃-C₆H₂)）发生反应，反应时其乙酸桥配体发生取代，得到一系列四核铜(II)膦酸盐配合物：[Cu₄(L)₂(t-BuPO₃)](CH₃OH)₂(C₆H₆)（1）、[Cu₄(L)₂(PhPO₃)(H₂O)₂(NMe₂CHO)](H₂O)₂（2）、[Cu₄(L′)₂(C₅H₉PO₃)](CH₃OH)₂（3）、[Cu₄(L′)₂(C₆H₁₁PO₃)](MeOH)₄(H₂O)₂（4）以及[Cu₄(L′)₂(C₃₀H₄₆P₂O₅)](PhCH₃)（5）。
对配合物1至4的分子结构解析结果显示，[RPO₃]²⁻配体通过4.211配位模式将四个铜原子桥联为一个整体。
在配合物5中，原位生成的[(RPO₂)₂O]⁴⁻配体桥联了两对双核亚单元。
针对上述配合物的磁性研究表明，膦酸配体是介导四个铜中心间磁相互作用的有效通道；低温条件下主要观测到反铁磁相互作用。