(Cyclen– and cyclam–pyridine)copper Complexes: The Role of the Pyridine Moiety in Cu^II and Cu^I Stabilisation

Abstract

Keywords:Copper / Cyclen and cyclam ligands / X-ray diffraction / UV/Vis and EPR spectroscopy / Electrochemistry / Configurational isomerisation

Synthesis and structural studies of two pyridine-armed reinforced cyclen chelators and their transition metal complexes

“…Structural comparisons with CB-Py 2 Cyclen [30] and PyCyclen [21] [22] (see Figure 1) are also desirable. Unfortunately, although Co 3+ , Cu 2+ , and Zn 2+ complexes with CB-Py 2 Cyclen, the most direct analogue including an ethylene cross-bridge, have been synthesized and characterized, no X-ray crystal structures have been published.…”

“…[13] The literature contains numerous other pyridyl pendant armed tetraazamacrocycles, indicating a general interest in the community and known synthetic techniques for adding pendant pyridyl donors. [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24]…”

Isomerism as a remarkable tool for the design of new potentially bridging macrocycle ligands: Synthesis and characterization of the [Cu(4-L1)](NO3)2·2H2O polymeric chain (4-L1=mono-N (4-picolyl)cyclen)

“…In contrast to the discrete complex [Cu(2-L1)](ClO 4 ) 2 ·2H 2 O based on the 2-L1 isomer [5], the crystal structure of 1, involving the 4-L1 macrocycle isomer, showed for the first time how a subtle isomeric change on the functionalized group allows drastic change of the coordination properties of such ligands.…”

“…In this context, a number of synthetic routes for the mono-, di-, three-and tetra-N-alkylation have been reported in the recent years [2,3]. This led to several series of metal complexes in which the functionalized tetraazamacrocycle acts as penta-, hexa-, hepta-or octa-dentate ligand [4,5]. Such metal complexes provide not only a basis for better understanding the metal environment in some metalloenzymes and metalloproteins, but also display catalytic properties, and as recently reported, original magnetic properties [6,7].…”

“…In these square pyramids, the basal plane involves almost equivalent bond lengths [2.012(2)-2.069(2) Å for Cu1-N and 2.005(2)-2.070(2) Å for Cu2-N] which are significantly shorter than the apical Cu1-N10 (2.139(2) Å) and Cu2-N5 (a) (2.154(2) Å) distances. As expected, the Cu environment in 1 is nearly similar to that observed in the parent discrete complex, [Cu(2-L1)](ClO 4 ) 2 ·CH 3 CN, involving the 2-L1 (mono-N (2-picolyl) cyclen) isomeric molecule for which the Cu environment exhibits a distorted square pyramid (Cu-N4 basal plane: 2.013(2)-2.058(4) Å and Cu-N apical position: Cu-N 2.164(4) Å) [5]. It should be noted also that the two Cu-N apical bond lengths in 1 (2.139(2) and 2.154 (2) Å) are slightly shorter than the corresponding distance (2.164(4) Å) observed for [Cu(2-L1)] 2+ complex involving the 2-L1 isomeric ligand.…”