| Abstract
| - The interaction with Cu2+ and dopamine of three polyazacyclophanes containing pyrazole fragmentsas spacers is described. Formation of mixed complexes Cu2+−macrocycle−dopamine has been studied bypotentiometric methods in aqueous solution. The crystal structures of the complexes [Cu2(L1)(H2O)2](ClO4)4·2H2O (4) (L1 = 13,26-dibenzyl-3,6,9,12,13,16,19,22,25,26-decaazatricyclo[22.2.1.111,14]octacosa-1(27),11,14(28),24-tetraene) and [Cu2(H-1L3)](HClO4)(ClO4)2·2H2O (6) (L3 = 1,4,7,8,11,14,17,20,21,24,29,32,33,36-tetradecaazapentacyclo[12.12.12.16,9.119,22.131,34]hentetraconta-6,9(41),19(40),21,31,34(39)-hexaene) are presented. Inthe first one (4), each Cu2+ coordination site is made up by the three nitrogens of the polyamine bridge, a sp2pyrazole nitrogen and one water molecule that occupies the axial position of a square pyramid. The distancebetween the copper ions is 6.788(2) Å. In the crystal structure of 6, the coordination geometry around eachCu2+ is square pyramidal with its base being formed by two secondary nitrogens of the bridge and two nitrogenatoms of two different pyrazolate units which act as exobidentate ligands. The axial positions are occupiedby the bridgehead nitrogen atoms; the elongation is more pronounced in one of the two sites [Cu(1)−N(1),2.29(2) Å; Cu(2)−N(6), 2.40(1) Å]. The Cu−N distances involving the deprotonated pyrazole moieties aresignificantly shorter than those of the secondary nitrogens. The Cu(1)···Cu(2) distance is 3.960(3) Å. Thepyrazole in the noncoordinating bridge does not deprotonate and lies to one side of the macrocyclic cavity.One of the aliphatic nitrogens of this bridge is protonated and hydrogen bonded to a water molecule, whichis further connected to the sp2 nitrogen of the pyrazole moiety through a hydrogen bond. The solution studiesreveal a ready deprotonation of the pyrazole units induced by coordination to Cu2+. In the case of L2(L2 =3,6,9,12,13,16,19,22,25,26-decaazatricyclo[22.2.1.111,14]octacosa-1(27),11,14(28),24-tetraene), deprotonation ofboth pyrazole subunits is already observed at pH ca. 4 for 2:1 Cu2+:L2 molar ratios. All three free receptorsinteract with dopamine in aqueous solution. L3 is a receptor particularly interesting with respect to the valuesof the interaction constants over five logarithmic units at neutral pH, which might suggest an encapsulation ofdopamine in the macrocyclic cage. All three receptors form mixed complexes Cu2+−L−dopamine. The affinityfor the formation of ternary dopamine complexes is particularly high in the case of the binuclear Cu2+ complexesof the 1-benzyl derivative L1.
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