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

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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 CuII 2 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 CuII 2 unit (–J= 229–357 cm–1 based on Ĥ=–2JS1·S2).
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