Synthesis and Crystal Structure of N-( 2-Pyridylmethyl )-L-Alanine ) Isothiocyanate Cobalt ( III )

The title compound, [N-(2-pyridylmethyl)-(L)-alanine]Co(III) thiocyanate (1) was obtained from the reaction of Co(OOCH3)2∙H2O with the tridentate reduced Schiff base ligand, N-(2-pyridylmethyl)-(L)-alanine (L) and NH4SCN and characterized by elemental analysis, IR, UV-visible, TGA and singlecrystal X-ray diffraction. Structural and spectroscopic analyses reveal [Co(L)2)]SCN to be monomeric with Cobalt(III) adopting a pseudo-octahedral geometry, coordinating to two reduce Schiff base ligands. In the crystal lattice, the thiocyanate anion forms an intermolecular SCN∙∙∙HNamine hydrogen bond, while adjacent monomers are linked by intermolecular Ocarboxyl∙∙∙HNamine∙∙∙H-bonds to form a supramolecular network. This work is therefore undertaken in an attempt to construct coordination framework structures of varying properties using the mixed-ligand strategy involving reduced Schiff bases and the thiocyanate ion.


Introduction
Cobalt complexes of Schiff base ligands are an important class of coordination compounds due to their structural diversity which display geometries ranging from tetrahedral, bipyramidal, square pyramidal to octahedral [1] [2] [3].Co-balt(III) complexes are generally prepared by air oxidation of Co(II) ion in the presence of relatively oxidation-inert ligands, which exhibit relatively strong coordinating abilities [4] [5].An effective method for the construction of coordination frameworks with interesting structures and properties is through mixedligand assemblies and reduced Schiff base ligands have been found to form flexible and multidentate network structures because of the reduction of the imine group, (-C=N-) of the Schiff base, thus overcoming ligand instability in complexes [6] [7].
Reduced Schiff base ligands have been found to be relatively inert towards air oxidation and are strongly coordinating due to the reduction of the N=C bond, giving rise to flexible multidentate ligands [8] [9].Pseudohalides possess versatile bonding modes, which result in the formation of complexes with various dimensionalities.The thiocyanate ions have therefore been found to possess versatile coordination abilities which result in the formation of metal complexes of varied structures.Thiocyanate-containing metal complexes have attracted much attention due to their versatile binding modes and its propensity to coordinate using either the nitrogen or/and the sulphur donor-atom, thus affording a number of homo-and hetero-metallic discrete structural assemblies with specific structural features and properties [10].
Recent attention has been focused on the study of the coordination compounds of cobalt due to its varied oxidation states and their interesting structural, magnetic, electronic and optoelectronic properties [11].Our focus has been on the synthesis of mixed ligand complexes involving tridentate reduced Schiff bases and the thiocyanate ion.The crystal structure of one such compound is reported here.

Physical Measurements
Elemental analysis for carbon, nitrogen and hydrogen were carried out on a FLASH 2000 Organic Elemental Analyzer, CHNS-O analyser by Thermo Scientific.Thermo Scientific iCAP 6000 SERIES duo ICAP Spectrometer was used to determine the metal content.Thermogravimetric analysis was investigated using a Mettler Toledo TGA/DSC1 STAR System; Infrared spectra were recorded on a Perkin-Elmer model IR-457 spectrometer and a spectrum 100 FT-IR Perkin Perkin-Elmer spectrometer, while the UV/Vis spectrum was recorded using an Agilent HP8453 Diode Array UV/Vis Spectrometer.The magnetic susceptibility measurement was made using the Sherwood Scientific magnetic susceptibility balance; while X-ray diffraction was carried using a Bruker APEX diffractometer.NH 4 SCN, (0.16 g, 2 mmol,) in 2 mL distilled water was added drop wise and stirring continued for a further two hours.Rectangular reddish brown crystals suitable for X-ray analysis were obtained from the solution by slow evaporation.Yield: 81%; anal.Calc.(Found) for C 19

Crystal Structure Determination
A suitable single crystal of the title compound was mounted on a glass fiber on the goniometer head of a Bruker APEX diffractometer and data were collected using graphite monochromated Cu-K α radiation (λ = 1.54178Å, operating at 50 kV and 40 mA) at a temperature of 100 K. Crystal data, data collection and structure refinement details are summarized in Table 1.
The structure was solved by direct methods and refined by full-matrix least squares on F 2 [12].All non-Hydrogen atoms were refined anisotropically.Hydrogen atoms were included in calculated positions, assigned isotropic thermal parameters and allowed to ride on their parent carbon atoms.All calculations were carried out using the SHELXTL package [13].CCDC 1419814 contains the supplementary crystallographic data for this paper.

Spectroscopic and Other Analysis
In the IR spectrum of the Co(III) complex, a very strong infrared absorption band at 1609 cm −1 is attributed to υ C=C and υ C=N of the pyridyl ring, while the strong band at 2098 cm −1 suggest the presence of N=C=S stretch [14] [15] [16], as confirmed by the single crystal structure of the compound.Two distinct peaks at 362 nm and 497 nm are observed in the UV-Visible spectrum of the complex and attributed to spin allowed d-d transitions.
The thermal behaviour of the title compound (Figure 1), recorded under an N 2 atmosphere, in the temperature range of 25˚C to 600˚C at a heating rate of 25˚C min −1 shows a one-step decomposition patterns at 310˚C though with a small shoulder at 240˚C which probably accounts for the decomposition of the

Conclusion
We have isolated a Co(III) Isothiocyanate metal-organic framework containing the chiral ligand, N-(2-pyridylmethyl)-L-alanine (pyala).Spectroscopic studies and the x-ray structure show that the compound is a monomer in which Cobalt(III) adopts a pseudo octahedral geometry, coordinating to two molecules of the ligand.Adjacent monomeric centres are linked by N-H…O, N-H…S hydrogen bonds which stabilize the compound thus forming a 3D supramolecular networks.

3 Figure 1 .
Figure 1.Thermal Analysis of the Title compound.

Figure 2 .
Figure 2. Ortep drawing of the Monomer of the titled compound (I) showing the atom numbering scheme.

Figure 4 .
Figure 4. Packing diagram the title compound.