Synthesis and Characterization of Mn ( II ) , Fe ( II ) and Co ( II ) Complexes with 4-Hydroxypiperidinedithiocarbamate and their Adducts with Neutral Bases

A new coordination complexes and adducts of the general formulas [M(hpipdtc)2] and [M(hpipdtc)2Ln] where M= Mn(II), Fe(II), Co (II), (hpipdtc)=4hydroxypiperidinedithiocarbamate, n=1 L= 1, 10phen, en, n=2 L=4-picoline, 3,5-luitidine, triphenylphosphine have been prepared and characterized by metal analyses, infrared, molar conductance measurements, electronic absorption spectra, and susceptibility measurements. Magnetic moments and electronic spectra, suggested tetrahedral geometry for complexes of the type [M(hpipdtc)2] and an octahedral geometry for their base adducts.


INTRODUCTION
Dithiocarbamates (R 2 CNS 2 -or DTCs) are monoanionic 1,1-dithio ligands they have been reviewed many times (Coucouvanis, 1970 ;Coucouvanis, 1979;Karlin, 2005).Among the ligands coordinating through sulfur atoms, dithiocarbamates are deserving much attention in recent years, and a large number of dithiocarbamate complexes have been synthesized so far; these compounds are being investigated in order to gain insight into the nature of the sulfur-metal bond in many biomolecules (Benigno et al., 2002).Dithiocarbamates derived from secondary amines are the most studied ones because they are stable and possess interesting electrochemical and optical properties (Onwudiwe and Ajibade, 2010).Dithiocarbamate complexes of divalent transition metals, in which the central atom is partially coordinatively unsaturated, are able to reversibly link molecules of organic S-, N-, P-donor bases.The resulting intermolecular heteroleptic complexes are generally called adducts (Tatyana et al., 2011).Dithiocarbamates are organosulfur compounds of robust synthetic and chemical properties (Siddiqi et al., 2007) and are produced in great quantities (Nabipour, 2011;Khwaja et al., 2006).The chemical properties of dithiocarbamates are due to the presence of one or more active group in their structures.This functional group can form complexes with almost all elements, including metal atoms of metal-containing enzymes, thus blocking their catalytic activity (Sanchez-Cortes et al., 1998).In this paper we present new dithiocarbamate complexes of some transition metals and their base adducts.

Materials and Methods
All reagents and solvents were commercially available high grade materials (Fluka A.G., Riedel-de Haën, BDH) and used as received, Infrared spectra were recorded on a Brucker Tensor 27co.FTIR spectrophotometer in the 400-4000 cm -1 range using KBr discs Conductivity measurements were carried out on 10 -3 M solution of the complexes in DMF using conductivity meter PCM3 Jenway at an ambient temperature.The electronic spectra were recorded on a Shimadzu UV-visible spectrophotometer UV-160 for 10 -3 M solutions of complexes in DMF as solvent at 25°C using 1 cm quartz cell.Metal content was determined spectrophotometrically using AA670 atomic absorption spectrophotometer.Melting points were recorded on an Electrothermal 9300 apparatus.The magnetic measurements were carried out at 25°C on the solids by Faraday's method using Brucker BM6 instrument.

I.A. Preprationof sodium 4-hydroxypiperidine dithiocarbamate,Na(4-hpipdtc)
4-hydroxypiperidine (10.1 g, 0.1 mol) was dissolved in 30 ml of water containing sodium hydroxide (4.0 g, 0.1 mol).The resulting solution was cooled in an ice bath, and carbon disulfide (7.6 g, 0.1 mol) was added dropwise with stirring.The mixture was stirred for 30 min, then allowed to be warmed to room temperature and stirred for an additional hour.The yellowish white precipitate formed, was filtered off, washed with diethyl ether and dried in vacuum.

Ι.D. Synthesis of adducts[M(4-hpipdtc) 2 L]
L=1, 10-phenanthroline, ethylenediamine Prepared similarly as in procedure (Ι.B) and after the formation of the precipitate, (0.005 mol) of (1,10-phenanthroline or ethylenediamine) was added with continuous stirring for 30 min.The complex formed was filtered and washed with methanol 10 ml, then dried under vacuum.

RESULTS AND DISCUSSION
The ligand was prepared by the reaction of carbon disulfide with the secondary amine 4-hydroxypiperidine in the presence of sodium hydroxide and the complexes were prepared by direct addition of the aqueous solution of the corresponding metal chloride to the ligand solution in aqueous methanol, using 1:2 (metal: ligand) molar ratio.The base adducts were prepared by adding the base to the prepared bis-complexes in (1:2) or (1:1) molar ratios.(Scheme 1).

Scheme 1: Synthesis of ligands, Mn(II), Fe(II), Co(II) dithiocarbamate complexes, and adducts
The composition and analytical data for all complexes are given in Table (1); IR and UV-Visible spectra data are shown in Table (2).The low values of molar conductivities of the complexes in DMF (0.9 -16.3 ohm -1 .cm 2 .mol - ) indicate that all the prepared complexes and adducts are non -electrolytes.(Geary, 1971) Infrared spectral studies: The most significant bands recorded in the IR spectra of the ligand and its complexes are reported in Table (2).For dithiocarbamate compounds, three main regions in the IR spectra are of interest.First the 1580-1450 cm -1 region, which is primarily associated with the stretching vibration of C-N group of (N-C) moiety (Srinivasan et al., 2010).The ligand shows a strong absorption at (1479) cm -1 , which is assigned to the C-N stretching frequency.The complexes show an absorption at (1486 -1516) cm -1 , which is assigned to the ν(C N) stretching frequency.Compared with the ligand, the ν(C-N)band of the complex is indeed shifted towards a higher frequency by (7-37) cm -1 .The υ(C=N)ring of 4-picoline,3,5lutidine and 1,10-phenthroline observed in the range (1441-1522) cm -1 (De Lima et al., 2011).
Second the (1060-940) cm -1 region, which is associated with ν (C-S) vibrations and a single absorption band observed in this region, suggests a bidentate behavior in dithio ligand.The complexes show bands at (966-1018) cm -1 assigned to ν (C-S) vibrations (Serrano et al., 2003).

Electronic spectral studies:
The UV-Visible spectra of the ligands and their complexes in 10 -3 M DMF solution were recorded; the results are listed in Table (2).The UV-Visible spectra of the Mn(II) complex give absorption bands at (31643-34013 cm -1 ), which corresponds to charge transfer transition.In the high spin d 5 manganese (II) configuration, the (d-d) electronic transitions are spin forbidden and laporate forbidden, due to the presences of five unpaired electrons.Therefore the absorption intensities decrease by a factor of about 100 compared to the usual (d-d) absorption band thus the spectra are not observed in the visible region (Al-Mukhtar and Mustafa , 1988).