If you were to Google "metal complexes of creatinine" you will found many examples, so no, there are no unique metals in this case.

Zinc was used in the 19th century to determine creatinine

Thank you sir for the information. I wanted to enquire about which property did they investigate while detecting creatinine uisng zinc?

At the end of the 19th century and at the beginning of the 20th century, creatinine was generally assayed using the Neubauer reaction (adding an alcoholic solution of zinc chloride to a creatinine-containing solution, yielding a complex with two molecules of creatinine and one molecule of zinc chloride). After weighing the precipitate and multiplying the result by 0.642, the amount of precipitated creatinine was found [Neubauer C. Ueber Kreatinin und Kreatin. Ann Chem Pharm 1866;137:288-298].

Thank you so much sir. 

However, it is important to note that Zn will form complexes with many other ligands in the presence of creatinine, so be careful about its exclusivity.

Thank you sir. I will definitely look into the interferences caused to Zn by other components.

Pls. find attched a file

Abstract

Creatinine   (2-amino-1-methyl-5H-imidazol-4-one)  occurs in vertebrate tissues and in urine. The mid and far infrared spectra of creatinine were recorded in the solid phase. The optimized structure of creatinine was obtained using DFT/B3LYP method with 6-311+G(d,p) and LANL2DZ basis sets. The harmonic frequencies of creatinine were calculated using DFT/B3LYP/6-311+G(d,p) method. The complete assignments were performed on the basis of the total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method. The creatinine-metal {cadmium [Cd(II)], zinc [Zn(II)] and mercury [Hg(II)]} halogen [chloride (Cl- ) and bromide (Br- )] complexes were synthesized. DFT calculations, DFT-B3LYP/LANL2DZ were performed for the determination of geometrical structure and vibrational assignment for metalcomplexes.

Manohar, be careful of your terminology - creatinine is NOT an amino acid.

Thank you Manohar Sir for the paper regarding creatinine metal complexes.

 This answer is:  

(a) more to say thanks to respected Dr. Joseph S Merola. I have  deleted the word amino acid  from my  previous answer.

(b) In addition, pls find references for  two more papers;

 the first containing   creatinine complexes of Co(II) while the second paper contains creatinine  complexes of  Pt(II) and Pd(II).

© Since  the authors of the second paper happen to be our worthy RG colleagues and thus the need.

{1}Transition Metal Chemistry

June 1984, Volume 9, Issue 6, pp 218-220

First online: 

Cobalt(II) complexes of creatinine

·                            Srinivasan Muralidharan

·                            , K. Seetharamiah Nagaraja

·                            , M. Ramakrishna Udupa

Summary

Cobalt(II) complexes of creatinine [Co(creat)2X2] (X = Cl, Br, I or NCS) and [Co(creat)2X2(H2O)2] (X = HCO2, HOCH2CO2 or CNCH2CO2) have been prepared. Their i.r. spectra show an increase in ν(NH) of the cyclic secondary amine group, compared to free ligand (3300 cm−1), indicating that cyclic nitrogen is involved in coordination. The thiocyanate group coordinates through nitrogen and carboxylates coordinate as univalent unidentate ligands. The electronic spectra and magnetic moments suggest a d7 configuration for cobalt: a tetrahedral geometry (4.4 B.M.) for halide and thiocyanate complexes, and an octahedral geometry (5.0 B.M.) for the carboxylate complexes. On heating, the ligand moiety is lost and the respective cobalt halide or cobalt carboxylate is formed, which is converted finally into Co3O4. There is a correlation between the high intensity electronic transitions and the polarographic half-wave potentials.

·                             

[II] Inorganica Chimica Acta., 137(1987) 131-134

 F. J. Martin-Gil and J. Martin -Gil

Thank you so much sir. I wanted to know if there has been any study on iron-creatinine complex.

[1] Quite a number of complexes have been  reported.

 [2] Find an other with Fe(II). The first three of four authors are our  worthy RG colleagues.

[3] Just fill google with

     Creatinine transition metal ion complexes

 Click and you  find  a few more  references  for 1st , 2nd and 3rd transition series metal ions complexes with creatinine

PM3, Ab Initio and Solution Studied of Some Transition Metal Complexes of Creatinine

Article · January 2011

 Jasmin Bhalodia,  Sangita Sharma , Dr. Jayesh Ramani,   Aashish Patel

Abstract

The interaction between transition metal ions like Cr(II), Co(II), Mn(II), Fe(II), Cu(II) and Ni(II) with Creatinine were studied both in gas phase and solution state. Solution state studies were conducted by using potentiometric technique by maintaining 1:1 ratio of species. For gas phase studies Ab initio 6-31G* and Polak Rabiera RHF-PM3 method is used. In solution state method it is found that creatinine has one protonable site and theoretical calculations explains creatinine as bidentate ligand and binds through oxygen and nitrogen (-NH Group) with selected bivalent metal ions. Binding effect is found in the order of Oxygen-Nitrogen > Oxygen > Nitrogen. Binding efficiency and binding modes is different for each metal ion. Creatinine forms high spin complexes with Cr(II), Fe(II) and Ni(II) with multiplicity of 5, 5 and 3 respectively and Mn(II) and Co(II) with multiplicity of 2 from low spin with highest binding energies. The results demonstrate that order of binding in solution phase is Cr(II) < Co(II) < Mn(II) < Fe(II) < Cu(II) < Ni(II).

Thank you so much sir. It has been really insightful. Thank you again.