Synthesis, spectra and structure of hydrazinium metal chloride and thiocynate complexes.

Abstract

Coordination compounds containing positively charged ligands occur rather seldom in marked contrast with neutral and negatively charged ligands. The presence of positive charge in the vicinity of a potential donor atom in a cationic ligand does not prevent coordination to an appropriate metal ion, even though the basicity is markedly lowered. In general, the effect of positive charge on the basicity of a donor atom depends upon their electronic interaction and their bonded distance within the ligand. Monoprotonated hydrazine, hydrazinium cation, N?H?? stands unique as it is the simplest analogue of the cationic ligands viz. (CH?)?–N?H?, (CH?)?–N?H?, HS–[(CH?)?]?–N, CH?S–[(CH?)?]?–N, (CH?)?S–[(CH?)?]?–NCH? and (CH?)?N–NH? in which the site of positive charge is immediately adjacent to the N-donor atom. Although the hydrazinium cation is a potential monodentate ligand, in some of the compounds it occurs as an uncoordinated cation. From the literature survey, it is seen that although exhaustive work has been done on hydrazinium metal sulphates, oxalates and hydrazinecarboxylates, very little is known about hydrazinium metal halides and pseudohalides (with the exception of hydrazinium metal fluorides). The present investigation aims at synthesis, characterization and thermal properties of hydrazinium metal chloride, bromide and thiocyanate complexes and also a study of the nature of coordination of N?H?? ion to various metal ions using spectroscopic and X-ray crystallographic studies. In the introductory chapter, a literature survey on the synthesis, infrared spectra, thermal analysis and structural studies on simple and complex hydrazinium compounds is presented. The scope and objectives of the present investigation are also highlighted. Chapter 2 describes the analytical procedures and instrumental methods employed in the present study. The instrumental methods employed include thermogravimetry, differential thermal analysis, magnetic susceptibility, infrared, electronic and Mössbauer spectroscopy along with single-crystal X-ray diffraction studies. Chapter 3 discusses the preparation, characterization and thermal analysis of (N?H?)?MCl?·2H?O, where M = Fe, Co, Ni, Cu, Pd and Pt. The crystal structure of iron and platinum complexes are described. The structure was solved by conventional Patterson and Fourier techniques and refined by full-matrix least-squares procedures. Structure of the iron complex shows that the metal is bonded octahedrally by two hydrazinium cations, two water molecules and two chlorides. The coordinated atoms are trans to each other. Structure of the platinum complex shows crystals containing discrete chloride ions, complex cations and water molecules. In the complex cation [Pt(N?H?)?Cl?]²?, platinum is coordinated by two chloride ions and two cations in trans positions. Preliminary studies show that in the cobalt complex the hydrazinium cations are in trans positions. Spectral studies show that in other complexes too hydrazinium cation is coordinated to the metals. Thermal analysis of the complexes shows that iron, cobalt, nickel and copper complexes decompose to the respective metal oxides through metal chlorides whereas platinum and palladium complexes decompose to the respective metals. The appendix of this chapter describes the preparation, characterization and thermal analysis of (N?H?)?MBr?·4H?O, where M = Co and Ni. Chapter 4 discusses the preparation, characterization and thermal analysis of a few anhydrous hydrazinium metal chloride complexes like CuCl?, (N?H?)?ZnCl?, (N?H?)?MnCl? and (N?H?)?FeCl?. The crystal structure of (N?H?)?MnCl? has been solved by conventional Patterson and Fourier techniques and refined by full-matrix least-squares procedures. The crystal contains discrete N?H?? cations and complex anions [Mn(N?H?)Cl?]?. In the complex anion, manganese is octahedrally coordinated by five chloride ions and one hydrazinium ion. Infrared spectra suggest that all the hydrazinium cations are coordinated in copper and zinc complexes, whereas in the iron complex only some of the four hydrazinium cations are coordinated to the metal. Mössbauer spectrum of the iron complex shows the presence of high-spin Fe²? ions in two different environments. TG-DTA studies show that the copper complex decomposes to metal through cuprous chloride. Other complexes decompose to the respective metal oxides via metal chlorides. In the appendix of this chapter, preparation, characterization and thermal analysis of (N?H?)?MnBr? are discussed. Chapter 5 of the thesis describes the preparation, spectra and structures of two thiocyanate complexes, (N?H?)?M(NCS)?·2H?O, where M = Co and Ni. Crystal structure of the cobalt complex has been determined. The structure contains [Co(N?H?)?(NCS)?] and water molecules. The cobalt atom is octahedrally coordinated by two ions and four thiocyanate groups. The thiocyanate groups are bonded to metal through N atoms. An interesting feature of the structure is that the two canonical forms of M–NCS linkage (bent and linear) are present in the same molecule. The two hydrazinium cations are in cis positions. Preliminary studies on the single crystals of the nickel complex indicate that it is isostructural with the cobalt complex. In the appendix of this chapter, crystal structure of a thiosemicarbazide complex, Ni(N?H?CSNH?)?(NCS)?, isolated during the preparation of the nickel complex, is described. In the structure, the nickel atom is octahedrally coordinated by two bidentate thiosemicarbazide molecules through S and hydrazinic N atoms and by two N-bonded thiocyanate groups.