Any method related to the nature of the valence electrons: UPS, XPS, ESCA, XAS

and, of course Moessbauer.

Sn119 NMR may also be of use .. XANES/ EXAFS spectroscopy definitely will solve your problem but access to it might be difficult as it only available at synchrotron source. Other techniques such as temperature programmed reduction/oxidation  (TPR/TPO) Can also be used to identify and quantify Sn2+ and Sn4+...

Mrs/Miss/Mr Ahlawat,

Remarkably easy you can do this by mass spectrometry. Please pay attention to an example (attachment) where we have shown theoretical and experimental isotopic shapes of SnII-species with relating refs.

Mr. Paech,

There is not nothing hidden, the example is even more than explicitly illustrative because of it is mono-nuclear complex of Sn.

So, when you have conducted mass spectrometric (MS) experiments they can be carried out under positive or negative operation modes. The shown example in the previous posting is experimental ESI(+)-MS data (meaning positive operation mode). When you have this mode, then your MS spectrum contains observable cations, which can be monocations and polycationic forms. They are explicitly determined, too. Each cation has exact isotopic shape depending on the elemental composition. When you have given composition of a metal-organic complex and this composition corresponds to a cation like the shown example of Na+ adduct of [SnCl2], meaning cation of [(SnCl2)Na]+, then to ensure a balance of 1+ charge of this cation, means that Sn has +2 oxidation state. If we have proposed +4, for example, then the total charge should be +3 for [(SnCl2)Na]3+ trication. However m/z should not be at the shown value 212. It should be, if this happen, at m/z (212)/3. Despite the fact that there are not stabilized trications. Usually are observed dications, so that MS isotopic shape sould be at m/z = MW/2 for dications.

Please pay attention to refs. [2-5], where have even more complex examples of di - and polynuclear complexes. In [Ref. 2] are shown dinuclear ZnII-containing organometallics, which ar enot so illustrative due to the stable oxidations tate of the ZnII - ion. But we have also example of cationic clusters of metal ions with unstable oxidation state such as Ag, Au, U, and more, where within the frame of a dinuclear positively charged Ag-complex, for example, with strictly fixed chemical content and structure, determined by MS/MS approach, there is possible to have a combination of following cations to each complex [X-AgIAgIII-Y]+, [X-AgIIAgII-Y]+, [XAgIIIAgI-Y]+, and s.o. They are characterized with different thermodynamic stability; or they are distinguishable as stability and chemical-physical properties. In our studied we have deduced oxidation state to each of metal ions employing quantum chemistry. In the cases of mixed metallic complexes (we have charged alloys compositios, too), the possible combination of oxidation states to each complex significantly increases in, along with a significant increasing in the structural isomers. The mean reason for this is that the metal ions in those complexes have different coordination environment, meaning different geometry of the metal chromophores. In this respect, the positive charge which is establish experimentally by MS (or doubly charge in dications) is not equally distributed over each metal ions in the given complex. This particularly is more illustrative shown in the case of composites [(M)nXYZ]+, [(M1)n(M2)mXYZ]+ [Ref. 4]. In this context there is possible to deduce the oxidation states of metal ion in polynucler mixed valence complexes (for example AuI/AuIII-, FeII/FeIII-containing complexes, like those in Refs. 4,5) as well as polynuclear mixed metallic and, in parallel, mixed valence complexes (for example AuIII/AgI -containing complexes).

[Ref. 2] Silver(I) and zinc(II) organometallic intermediates, catalysing coupling reactions of polysubstituted benzoic acids - Experimental and theoretical study, Bojidarka Ivanova, Michael Spiteller, Chemical Engineering Journal, Volume 232, October 2013, Pages 118-127

[Ref. 3] Organosilver(I/II) catalyzed C-N coupling reactions-phenazines, Bojidarka Ivanova, Michael Spiteller, Catal. Sci. Technol., 2013,3, 1129-1135

[Ref. 4] Adsorption of uranium composites onto saltrock oxides - experimental and theoretical study, Journal of Environmental Radioactivity, 135, 2014, 75-83

[Ref. 5] Study of sorption of uranium ions onto Fe-containing minerals using UV-MALDI-MS and theoretical quantum chemical modelling

Bojidarka B. Ivanova, Michael Spiteller,Water Air and Soil Pollution 11/2014; DOI:10.1007/s11270-014-2208-2 (http://www.researchgate.net/publication/268211751_Study_of_sorption_of_uranium_ions_onto_Fe-containing_minerals_using_UV-MALDI-MS_and_theoretical_quantum_chemical_modelling)

Article Study of sorption of uranium ions onto Fe-containing mineral...

I agree with Michael, MS cannot generally be used as a method to determine the oxidation state of an element in a complex. Of course, if you have simple species such as [SnClx]y+, the oxidation state of Cl is clearly -1 and then you can deduce the oxidation state of Sn from x and y (from MS data).

I have characterized the complexes with 119Sn NMR spectra, there was single sharp singlet peak, but can any one of you tell me how to find out the oxidation state through 119Sn spectra,??  Can you give me references??? 

This might not be the best answer but have you considered the use of "predictive charts" such as the one given in this website?

chem.ch.huji.ac.il/nmr/techniques/1d/row5/sn.html#sn119

There are a number of references at the end of this webpage which could potentially help you, in the absence of mossbauer data.

Here is a recent paper where computational methods was employed to rationalize NMR data of Sn(II) compounds.

http://pubs.acs.org/doi/abs/10.1021/om5007566

If I may add: a little more data in your question (on the nature of the compounds / reactions etc) might really help fellow researchers to provide you with specific answers.

Good luck

may also be of use magnetic susceptibility calculation