What are the space groups of the different possible complexes? If they differ from one another maybe IR -pectroscopy may give some insight (with additional electronic simulation of the different complexes); this might be helpful to decide whether a sigma-donor-ligand is cis or trans to a pi-acceptorligand (e.g. a chloro-ligand cis or trans to a carbonyl-ligand).

Mr. Kalinke,

You can use UV-VIS and IR methods as it was already pointed out.

However, you should employ polarized measurements, accompanied with corresponding theoretical quantum chemical analysis of the electronic structure and transitions. With conventional measurements (and computations) there is unable to deduce the structure of complex.

The employment of IR-based approach increases the reliability of your deduced structure, because of IR-bands are not so broad, by contrast to UV-VIS ones. They are not so overlapped (frequently) as well. And in addition, they are a larger number. The latter is among the most important factor associated with reliability of your deduction, because of, you can confirm your assumption about structure of a complex using a larger set vibrational modes within the framework of a larger range of electromagnetic spectrum, comparing with the UV-VIS one. Or you can use set independent vibrational modes of a given chromophore to confirm your structure. These vibrational modes can be predict by the quantum chemical methods at a high level of accuracy.

Particularly, highlighting employment of linear polarized IR measurements for structural analysis, you could pay attention to the following book and associated reference section:

https://books.google.de/books?id=x2Cabv83pM4C&pg=PA197&lpg=PA197&dq=IR-LD+spectroscopy+ivanova&source=bl&ots=oSAsOboDdU&sig=jU_ZUtMkWJbpFRC94VFmXb2ugEg&hl=de&sa=X&ved=0ahUKEwjk_Ibes_rOAhWH1xQKHZJXCUMQ6AEIPzAD#v=onepage&q=IR-LD%20spectroscopy%20ivanova&f=false

For a large number of objects, the reliability of polarized IRLD/quantum chemistry is compared with single crystal XRD data.

you can use the 1H NMR

Kamel Landolsi, for Co(II) and Cu(II) NMR spectroscopy is not suitable since they are paramagnetic species (7 and 9 d-electrons). 

Dear Lucas,

Please, find in attached a contribution on: predicting complex geometry

Hoping to be helpful

Dear Lucas,

(EXAFS) SPECTROSCOPY is very useful for determination of complex geometry

EXAFS Spectroscopy: a Brief Introduction*

Gilberto Vlaica,b,c,** and Luca Olivib

CROATICA CHEMICA ACTA

CCACAA 77 (3) 427¿433 (2004)

ISSN-0011-1643

CCA-2944

Review

Dear Lucas

It is possible to predict complex geometry by spectroscopic methods. UV Visible spectroscopy is very helpful for this. You should read the book entitled "

A. B. P. Lever; “Inorganic Electronic Spectroscopy”, Elsevier Amsterdam, 1984.

1 H NMR and ESR spectroscopic methods may also help you.

N. Tidjani- Rahmouni

I wonder who was downvoted may answers, what is wrong ?. I invite him to read about  EXAFS Spectroscopy to know that it is very useful for determination of complex geometry.

Dear Peter

It doesn't matter if one provide a method or technique other than that in the question, perhaps it give more options to him. All what I've done is providing a solution other than UV-Vis spectroscopy.

Thanks a lot

Uv-vis can provide comparative information in this case. You will need to have a spectrum of the different geometries and then you can figure out which is which base on the CFSE. The CFSE of Oh should be greater than Td and if that it is the case, you would expect the Oh complexes to have transitions at lower wavelengths compared to the Td complexes. You can also identify the element you are working with based on the expected number of transitions but Uv-vis coupled with variable temperature magnetic susceptibility measurement in most cases should be enough to provide some reliable information.