Mrs/Miss Grover,

Please find as attachment an EPR spectrum, having near Sq planare geometry of CuO2N2 chromophore, describing this geometry in terms as a structure result of an infinite elongation within the frame of an Oh one (page 1, attachment) along the z-axis, due to Jahn-Teller’s effect. Z is perpendicularly disposed towards the plane of CuO2N2 chromophore.

In a Cu-porphyrin complex (oxidation state +2, d9 electronic configuration) we can expect an almost Sq geometry of CuN4 or CuN4(H2) chromophores, too, because of porphyrin as ligand has similar coordination behaviour towards many transition metal ions.

However we can expect a significant hyperfine splitting of each of the components in the psctrum, determining by Zeeman's effect, because of at it was shown in page 2 (attachment) the number of the components has been determined by the nuclear spin of the ith and jth nuclei and their number.

Thus:

1.If the complex is 2+ positively charged one (i.e. CuIIN4(H)2 chromophore, solution), than in the shown example IO=0 and there hav ebeen accounted only the two N. But in the case of a porphyrin complex, we can expact (2.2H.1+1)(2.4N.1+1) components, nevertheless that CuII - ions should be bonded to the four N-centres via only coordinative bonds.

2. If the complex is neutral, meaning CuN4 chromophore, obtained through deprotonation of NH-groups in the porphyrin, than we can expect (2.4N.1+1) splitting components.

Dear Bojidarka B. Ivanova,

Thanks for your answer . But can you suggest what will happen when porpyrin itself nonplannar whatever you told it is absolutly fine for planar porphyrin- cu complexes.

Main change is a decrease in spin density on the Cu and N upon saddle distortion, and a decrease in the hyperfine couplings; see Eur J Inorg Chem 2005, 1609. For the main effects of distortion on EPR see: J. Phys. Chem. A 1994, 98, 2520 and 1999, 103, 1950. Can't recall EPR studies on ruffled porphyrins, you might want to look at Nakamura's work with iron porphyrins.

Mrs/Miss Grover,

Porphyrin as molecular skeleton is widely used for modelling and optimization of the photophysical properties of organic and metal-organic optical materials.

One of the reasons is that this fixed chelating fragment has yielded coordination compounds with large set of metal ions. I do not comment here it coordination behaviour with FeII/FeIII ions. There have numerous studies in this topic as well.

But, despite that the crystallographic reports of metal - organic complexes with porphyrin itself are scarce, there have numerous studies on scaffolding and modelling of simply functionalized derivatives such as the shown representatives in the attachment. Ref [2d], for example, has involved information about 200 crystals of metal ions with porphyrins. Please take into account that this cannot be regarded as a comprehensive literature research exactly on the coordination ability of porphyrins. Typically even with metal ions such as FeII/III, or even RuII/III which yield complexes with different coordination numbers such as the few examples of square pyramidal FeII/IIIN4X  (X = O or Cl) and FeII/IIIN4XY (X=O, Y=N) complexes (pages 5 and 9, refs. [8,15]) or octahedral FeN4O2 one (page 7, ref. [12]), there have, like many other metal ions, complexes with MN4 geometry of the chromophore (ref. [2d]). Considerable number of crystallographic reports have shown MN4 chromophore of porphyrin complexes with several ions shown in page 2. Same structure of the chromophore with For FeII/III complexes (i.e. FeN4) has been demonstrated in refs. [2d,5c]. Most probably, even, there have other examples, too. So that to obtain a MN4 chromophore with CuII ion, interacting with ligand such as porphyrin has high probability.

Furthermore, as can be seen (also attachment), particularly, for CuII complexes, I have found two EPR reports (page 1, refs. [1a,3]). In the first case of a CuII-porphirin complex (there have not shown EPR spectrum) the g-values have been discussed (page 1). The ref. [3] has reported same g-values and has provided a spectrum (page 1). These data have confirmed a CuN4 coordination in almost square planar geometry of the chromophore for two different complexes with modified porphyrine skeleton, accoreding my previous comments.

In addition, two crystallographic reports of CuII-complexes (pages 2 and 4; refs. [2d,7]) are also know and they have shown CuN4 chromophore in the crystalline state in a Sq geometry.

Dear Bojidarka B. Ivanova,

Thanks for your kind suggestions and pdf file . 

I know about EJIC 2005 Abhik Ghosh's article in which author discussed about EPR, ENDOR, and theoritical studies but i didn't know about other two. Thanks for your kind suggestion. 

Mrs/Miss Grover,

Even may have more references, bacause a fast look on the data available have shown ca. 56 000 papers of porphyrin and about 2100 crystallographic reports. Most probably there are known other examples of Cu-complexes - crystal structure and EPR data.