X-RAY STRUCTURES OF MONONUCLEAR AND DINUCLEAR CU(II) COMPLEXES OF NOVEL PYRIDINE CROWN-ETHER LIGANDS

Two novel pyridine-crown ether ligands, 1 and 2, have been synthesized by high-pressure additions of monoaza-15-crown-5 and diaza-18-crown-6 , respectively, to 2-vinylpyridine. Treatment of ligand 1 with 1 equiv of Cu(ClO4)(2).6H(2)O results in the formation of a mononuclear coppe r(II) complex 3, which crystallizes, as revealed by single-crystal X-r ay diffraction, in the monoclinic space group P2(1)/c (No. 14) with a = 8.4636(10) Angstrom, b = 15.912(5) Angstrom, c = 19.373(4) Angstrom, beta = 110.341(16)degrees, V = 2446.3(1.0) Angstrom(3), and Z = 4. Th e structure refinement converged to R = 0.040 and R(w) = 0.050. The co pper(II) ion in 3 is surrounded by two crown ether oxygen atoms and tw o nitrogen atoms as well as by an oxygen atom of a methanol molecule w hich is bound in the crown ether ring. The geometry around the metal c enter is that of a distorted trigonal bipyramid. Addition of 1 equiv o f Cu(ClO4)(2).6H(2)O to ligand 2 yields a dinuclear Cu(II) complex (4) , which coprecipitates with the bisprotonated ligand 2. The X-ray stru cture of 4.2.2HClO(4) reveals a monoclinic space group C2/c (No. 15) w ith a = 26.4295(12) Angstrom b = 9.8275(4) Angstrom, c = 26.8414(15) A ngstrom, beta = 104.272(4)degrees, V = 6756.5(6) Angstrom(3), and Z = 4. The structure refinement converged to R = 0.078 and R(w) = 0.071. C omplex 4 consists of a dinuclear [Cu-2(OH).2](3+) cation, With a perch lorate anion bound to it through a bifurcated hydrogen bond to the bri dging hydroxo group. Each copper ion is 5-fold coordinated, viz. by tw o nitrogen and two oxygen atoms from the crown ether moiety and a brid ging hydroxo group. Both copper ions have a trigonal bipyramidal envir onment. Ligand 2 is protonated on the amine functions present in the c rown ether ring. Each proton forms a trifurcated II-bond with two crow n ether oxygen atoms and a pyridine nitrogen. Complex formation in sol ution proceeds stepwise both for 3 and 4. At low Cu(II) to 1 ratios, t wo ligands molecules 1 coordinate to one Cu(II) ion. This intermediate reacts further at higher copper(II) concentrations to yield complex 3 . Complex 4 is formed via a mononuclear copper(II) complex which is th ought to have a structure simular to that of complex 3. Both 3 and 4 u ndergo irreversible oxidations in acetonitrile solution, at +0.04 and -0.36 V vs Fc/Fc(+), respectively.