Macrocyclic ‘dimer-of-dimers’ type tetranuclear copper(II) complexes with two bridging hydroxy groups in a face-to-face manner

Abstract

Macrocyclic tetranuclear copper(II) complexes of the general formula [Cu₄L(OH)₂][X]₂[Y]₂(L = L¹, X = Y = CIO₄^– or X = MeCO₂, Y = PF₆; L = L², X = Y = CIO₄ or X = Y = PF₆^–) have been obtained by template reactions, where L denotes the macrocycles formed by the [2 + 2] condensation of 2,6-diformyl-4-methylphenol with 3,6-diazaoctane-1,8-diamine (L = L¹) or 3,6-dithiaoctane-1,8-diamine (L = L²). The very efflorescent solvate complex [Cu₄L¹(OH)₂][MeCO₂]₂[PF₆]₂·4MeCN·2PrⁱOH crystallizes in the monoclinic crystal system, space group P2₁/a, with a= 13.038(5), b= 21.251(5), c= 12.757(3)Å, β= 113.38(2)°. The refinement converges with R= 0.1215 and R′= 0.1187. The tetranuclear cation {Cu₄L¹(OH)₂(PrⁱOH)₂(MeCN)₂}⁴⁺ contains two dinuclear Cu^II₂ units in a ‘dimer-of-dimers’ arrangement. In each unit two copper(II) ions are bridged by an endogenous phenolic oxygen of (L¹)^2– and an exogenous hydroxide oxygen with a Cu ⋯ Cu separation of 2.949(4)Å. A propan-2-ol molecule resides on the axial site of one copper ion and an acetonitrile molecule on the axial site of the other copper ion, affording a square-pyramidal geometry about both copper(II) ions. The two dinuclear skeletons assume a near coplane and the two bridging OH^– groups are facing each other with an O ⋯ O separation of 3.32(2)Å. The efflorescent solvate complex [Cu₄L²(OH)₂][PF₆]₄·4MeCN·4H₂O crystallizes in the triclinic crystal system, space group P, with a= 12.576(9), b= 13.082(6), c= 11.682(6)Å, α= 109.54(4), β= 106.99(5), γ= 69.02(5)°. The refinement converges with R= 0.0835 and R′= 0.0812. The centrosymmetric cation {Cu₄L²(OH)₂(MeCN)₄}⁴⁺ assumes a similar ‘dimer-of-dimers’ structure with two facing OH^– groups where an acetonitrile molecule co-ordinates at the axial site of each copper(II) ion. The Cu ⋯ Cu separation in the dinuclear unit is 2.976(2)Å and the O ⋯ O separation between the two facing OH^– groups is 3.80(1)Å. In all the tetranuclear complexes the two dinuclear units are magnetically isolated from each other and a significant antiferromagnetic interaction operates within each Cu^II₂ unit (–J= 229–357 cm^–1 based on Ĥ=–2JS₁·S₂).