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Tailoring the local environment around metal ions: solution chemical and structural study of some multidentate tripodal ligands


Manganese(II), copper(II) and zinc(II) complexes of four polydentate tripodal ligands (tachpyr (N,N’N’’-tris(2-pyridylmethyl)-cis,cis-1,3,5-triaminocyclohexane), trenpyr (tris[2-(2-pyridylmethyl)aminoethyl]amine, tach3pyr (N,N’N’’-tris(3-pyridylmethyl)-cis,cis-1,3,5-triaminocyclohexane) and tren3pyr (tris[2-(2-pyridylmethyl)aminoethyl]amine)) were characterized in both solution and solid states. Combined evaluation of potentiometric, UV-VIS, NMR and EPR data allowed concluding both thermodynamic and structural information on the complexes formed in solution. The four tailored polydentate tripodal ligands studied here offer high thermodynamic stability, and a variety of coordination environment/geometry for the studied transition metal ions. Our data indicate that tachpyr is more efficient zinc(II) and similar copper(II) chelator than trenpyr. Considering the higher number of N-donors and conformational flexibility of trenpyr, as well as the energy demanding switch to the triaxial conformation required for metal ion binding of tachpyr, the above observation is surprising and is very likely due to the encapsulating effect of the more rigid tachpyr skeleton. This relative binding preference of tachpyr for zinc(II) may be related to the observation that zinc(II) is one of the principal metals targeted by tachpyr in cells. In contrast, trenpyr is considerably more efficient manganese(II) chelator, since it acts as a heptadentate ligand in the aqueous Mn(trenpyr) complex. The crystal structures of copper(II) and zinc(II) complexes of tachpyr indicated important differences in the ligand conformation, induced by the position of counter ions, as compared to earlier reports. The closely related new ligands, tach3pyr and tren3pyr have been designed to form oligonuclear complexes. Indeed, we obtained a three dimensional polymer with copper(II)/tren3pyr ratio of 11/6. Within this metal-organic framework three distinctly different copper geometries can be identified: square pyramidal, trigonal bipyramidal and tetrahedral. Two square pyramidal and four trigonal bipyramidal copper centres create a hexanuclear subunit with a large inside cavity. These moieties are linked by tetrahedral copper(II) centres, constructing the three dimensional polymer structure. The formation of such polynuclear complexes were not detected in solution. Both tach3pyr and tren3pyr form only mononuclear complexes with square pyramidal and trigonal bipyramidal geometry, respectively.

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Publication details

The article was received on 11 Jan 2017, accepted on 06 Jun 2017 and first published on 06 Jun 2017

Article type: Paper
DOI: 10.1039/C7DT00104E
Citation: Dalton Trans., 2017, Accepted Manuscript
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    Tailoring the local environment around metal ions: solution chemical and structural study of some multidentate tripodal ligands

    F. Matyuska, A. Szorcsik, N. V. Nagy, Á. Dancs, É. Kováts, A. Benyei and T. Gajda, Dalton Trans., 2017, Accepted Manuscript , DOI: 10.1039/C7DT00104E

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