Document Type



Doctor of Philosophy (PhD)



First Advisor's Name

Raphael G. Raptis

First Advisor's Committee Title

Committee Chair

Second Advisor's Name

Konstantinos Kavallieratos

Second Advisor's Committee Title

Committee Member

Third Advisor's Name

Yuan Liu

Third Advisor's Committee Title

Committee Member

Fourth Advisor's Name

Xuewen Wang

Fourth Advisor's Committee Title

Committee Member

Fifth Advisor's Name

Stanislaw Wnuk

Fifth Advisor's Committee Title

Committee Member


Pyrazole, Pyrazolate, Chromium, Iron, Trinuclear Complexes, Ferric Compounds, Mixed-valent iron, Crystallography, X-Ray, Electrochemistry, EPR, Dynamic NMR

Date of Defense



The main objective of this project is to synthesize the first family of polynuclear chromium pyrazolate complexes. Complexity in analysis of the experimental magnetic data of multinuclear complexes arises from their (2S +1)N microstates, where S is the spin of each metal center and N is the number of metal centers. For example, high-spin (HS)-FeIII3 has 216 microstates and HS-FeIII8 ≈ 1.7x106 microstates (S= 5/2). However, complexes with chromium(III) S = 3/2 will have a noticeable reduction of microstates. Mononuclear complexes with formula [mer-CrCl3(pzH*)3] (pz*H = pyrazole, 3-Me-pzH, 4-Me-pzH, 4-Cl-pzH, 4-I-pzH, 4-Br-pzH) and [trans-CrCl2(pzH*)4]Cl (pzH* = pyrazole and 3-Me-pzH) were synthesized and thoroughly characterized. Polynuclear iron pyrazolate complexes are prepared by the addition of base to [mer-FeCl3(pzH*)3] and [trans-FeCl2(pzH*)4]Cl complexes; the path is not paralleled by mononuclear chromium(III) pyrazole complexes. There is a challenging situation with these reactions, caused by the attainment of equilibrium, where the stable mononuclear complexes and traces of dinuclear species coexist in solution. Microwave assisted reaction of Cr(NO3)3·9H2O and pyrazole ligand in dimethylformamide (DMF) solution afforded redox inactive trinuclear formate-pyrazolate mixed-ligand complexes with formula [Cr33-O)(μ-O2CH)3(μ-4-R-pz)3(DMF)3]+ (pz = pyrazolate anion; R= H, Me, Cl). Thermally assisted synthesis with non-hydrolysable solvent yielded an electrochemically active all-pyrazolate complex. Complex with formula (Ph4P)2[Cr33-O)(μ-4-Cl-pz)6Cl3] and (Ph4P)2[Cr33-O)(μ-4-Cl-pz)6Br3] have an oxidation process at 0.502 V at 0.332 V, respectively. The latter has a second accessed oxidation process at 0.584 V. These systems are the first example of electrochemically amendable trinuclear pyrazolate complex with {Cr3O} core.

The all-ferric complexes [Fe33-O)(μ-4-NO2-pz)6(L)3]2- (L = NCO-, N3) were synthesized from reaction of [Fe33-O)(μ-4-NO2-pz)6Cl3]2- with NaNCO and NaN3. Expected reversible reduction processes were observed for both complexes at more negative potential, -0.70 V, compared to the thiocyanate complex (-0.36 V). The 57Fe Mössbauer of the reduced [Fe33-O)(μ-4-NO2-pz)6(N3)3]3- is suggestive of a HS-to-LS electronic reorganization, as seen for the [Fe33-O)(μ-4-NO2-pz)6(SCN)3]3- complex. Furthermore, compound [Fe33-O)(μ-4-NO2-pz)6(N3)3]2-, shows a unique reversible oxidation process at 0.82 V (vs. Fc+/Fc) to a mixed-valent, formally Fe3+2/Fe4+ species.





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