Dear Sudheer Yadav thank you for your interesting technical question. As to the best of my knowledge, most hexakis(urea)manganese complexes contain trivalent manganese. Thus far I found no reference in which the compound [Mn(urea)6](NO3)2 has been reported. The only potentially useful reference I found is the following article entitled:

Coordination of manganese(II). High spin complexes with urea

Article Coordination of manganese(II): High spin complexes with urea

In this paper the manganese(II) complex [Mn(urea)6](ClO4)2 is reported. I'm not sure if the corresponding nitrate salt has ever been described.

It's a typical question of choosing the solvents and conditions. See the attached paper

Interesting question

Thank you for the answers, hexakis Manganese urea nitrate complex is reported but by solid-state method though the author has not described the process. Dear Frank T. Edelmann and Paul Milham please find the attached paper.

Dear Sudheer Yadav many thanks for sharing the relevant article published in the Journal of Thermal Analysis and Calorimetry. This paper is a typical example of a common scientific bad habit. The authors present a fragmented study and announce that the synthesis of the title compound and other details will be "presented elsewhere". The respective Reference [3] lists a paper in Revue Roumaine de Chimie which is "in press". however, when you check this journal for the authors' names you find that this paper has never been published. Thus I'm afraid that details about the synthesis of [Mn(urea)6](NO3)2 have never really been disclosed.

Frank T. Edelmann Yes that's true. However, after several trials, I have successfully grown crystals of Mn-urea nitrate complex by solution method. The compound I obtained is Mn(urea)4(NO3)2 and not [Mn(urea)6](NO3)2.