Transition Elements and Coordination Compounds Analysis

Transition Elements and Coordination Compounds Analysis Manganese is a first row transition metal that has varies type of oxidation states when it appears as a compound. The oxidation range is from Mn(-III) till Mn(VII). This has shown that the compounds of manganese range in the oxidation number have a different of 10 electrons. The experiment 1 that we have done is changing oxidation state of manganese(II) chloride to an acetylacetonemanganese(III) with an oxidizing agent potassium permanganate. However, the main target compound that we are interested in this experiment 1 is the characterize complexes of 2 metal ions with the anion of acetylacetone. This compound is actually a typical a-diketone that can ionize in an aqueous solution as a weak acid. This is the main reason that the acetylacetonate anion will serve as a ligand towards metal ion and form new complexes. The ligand will bond to the metal through 2 oxygen atoms to form a six-membered ring. These six-membered rings (MO2C3) are in a planar shape and it is a weak aromatic. This is due to that they contain 6 Ï€ electrons. Thus, in the complexes of stoichiometry M(acac)3, there will be in a few different shapes. Such as the MO6 array is octahedral, for Cu(acac)2, the CuO4 group will be in square planar, and lastly for VO(acac)2, the VO5 group is in square pyramidal. As a result, the complexes are neutral in charge and they may be isolated as crystalline solids with interesting variety of colors. The equation for this experiment will be: MnCl2 + 4H2O → [Mn(H2O)4]Cl2 [Mn(H2O)4]Cl2 + 2HC5H7O2 + 2NaC2H3O2 → Mn(C5H7O2)2 + 2NaCl + 2HC2H3O2 Mn(C5H7O2)2 + KMnO4 + 7HC5H7O2 + HC2H3O2 → 5Mn(C5H7O2)3 + KC2H3O2 + 4H2O Cobalt is also another transition element that we are using in this experiment to form a coordination complexes. The cobalt 2+ ion is more stable than the cobalt 3+ ion for simple salts of cobalt. Therefore, there are only a few salts that are form with Co(II). However, the forming of complexes will eventually have a more stable oxidation state compare to the oxidation state of Co(II). In octahedral coordinated complexes, the number of complexes appears in a very stable conformation. Werner coordination complexes are compounds that formed between a transition metal ions and variety of organic and inorganic ions or neutral molecules. For both chloropentaamminecobalt(III) chloride and tris(acetylacetonato)manganese(III) also forms the octahedral coordination. In these complexes, it contains of six ligands (L) and a central atom (M) at the apices of an octahedron. For this experiment, the equation will be written as: Co2+ + NH4+ + 1/2H202 → [Co(NH3)5H2O]3+ [Co(NH3)5H2O]3+ + 3Cl- → [Co(NH3)5Cl]Cl2 + H2O Vanadium is also a transition element where it also exits in a variety of oxidation states which is from -3 to +5. Each of it undergoes a wide variety of chemistry depends on the electronic and steric nature of the coordinating ligands of it. For an example, in a higher oxidation states, vanadium is very oxophilic, but at low oxidation states, the Ï€-donating ligands such as dinitrogen and carbon monoxide are preferred. Therefore, the +4 and +5 states for vanadium are more important in biological reactions. The vanadium(IV) is dominated by the stable oxovanadium (VO2+) cation that remains intact during many reactions. While the deoxygenation of oxovanadium(IV) complexes to form a six-coordinate vanadium(IV) complexes will usually enhances their reactivity. In this situation, vanadium that is also a strong oxidizing agent will actually undergo redox in high possibilities when it involve in the reaction with organic molecules. Majority of vanadium(IV) complexes depend upon oxovanadium ion VO2+ complexes and the color for it is generally green or blue-green. This compound has oxygen atoms coordinating in the equatorial plane where the apical coordination will be the oxo group that complete the square pyramidal geometry coordination. It acts as a good precursor and undergoes ligand exchange reaction where one or both of the acetlyacetonato groups can easily be exchanged with organic ligands that having coordinating of different potentialities. For both of the complexes above is all in hexacoordinate with octahedral. However, there are many examples of coordination chemistry with coordination numbers from 3 to 9. Pentacoordinate complexes are much less common than either tetra- or hexacoordinate. This is more common for some metals, compound with one oxidation state and some others rare compound. There are mainly two types of geometries for it which is trigonal bipyramidal and square pyramidal. The bis(acetylacetonato)oxovanadium(IV) is our product in this experiment 3. In this experiment, the equation for it can be written as: V2O5 + 2H2SO4 + EtOH 2VOSO4 + 3H2O + CH3CHO VOSO4 + 2HC5H7O2 + Na2CO3 VO(C5H7O2)2 + Na2So4 + H2O + CO2 Discussion: Interpretation of IR spectrum for tris(acetylacetonato)manganese(III): Wavenumber (cm-1) Description of bands 1635.2 1506.5 -relative intensity : strong -(C=C) stretching -(C=CH) deformation 1386.9 -relative intensity : strong -(CH3)- symmetric C-H deformation 1255.6 -relative intensity : strong -(C=C) stretching -(C-CH3) stretching 1014.8 -relative intensity : strong -(CH3) out-of plane bending 924.5 -relative intensity : strong -(C-CH3) stretching 785.6 -relative intensity : strong -(C-H)deformation 678.1 -relative intensity : medium/ strong -(C-CH3)stretching,(O=C-CH3) deformation -(Mn-O) stretching indicates metal-ligand bond 458.3 relative intensity : weak (C=C) stretching,(C-CH3) stretching -(Mn-O) stretching that also indicatesmetal-ligand bond Interpretation of IR spectrum for bis(acetylacetonato)oxovanadium(IV): Wavenumber (cm-1) Description of bands 1559.0 1532.9 -relative intensity : medium (C=O) stretching -( C=C),(C=CH) stretching 1419.0 -relative intensity : medium -(CH3) deformation 1374.3 1357.9 -relative intensity : strong -(C=O) stretching -(CH3) deformation mode 1287.0 -relative intensity : strong -(C=C=C) stretching 997.4 -relative intensity : strong and sharp -stretching of V=O bond -it also indicates the metal-ligand bond.(1) 1021.7 -relative intensity : strong -(CH3) rocking 937.0 -relative intensity : strong -(C-CH3) stretching -(C=O) stretching 798.7 -relative intensity : medium -(C-H) out-of-plane bending 686.0 657.1 -relative intensity : medium/ weak -(ring) deformation out-of-plane bending for: 609.6 -(ring) deformation Interpretation of IR spectrum for chloropentaamminecobalt(III) chloride: Wavenumber (cm-1) Description of bands 1635.0 1559.0 -relative intensity : medium -degenerate asymmetric NH3stretching 1304.8 -relative intensity : strong -symmetric NH3angle deformation 837.7 -relative intensity : strong -NH3rocking 669.2 -(Co-N) stretching indicates metal-ligand bond(1) 486.2 -(Co-Cl) stretching indicates metal-ligand bond(1) There are suppose to have a symmetric NH3 stretch, 3169.3 cm-1 and an asymmetric NH3 stretch, 3289.3 cm-1 in the IR spectrum. These two spectrums are important to prove that there are two different chemical conditions for this NH3 ligand in this complex. This condition is actually due to the distortion geometry by chloride ligand. From 3 of the IR spectrum that we had obtains is that we are able to identify two error in it. First is the peak that going upwards at the region between 2000 cm-1 and 2500 cm-1. This error is due to the FT-IR spectrometry error as it can be shown in the comparison between the second IR spectrums that read by another spectrometry. Then, the following error is the very strong H2O that is mixed within the compound when we are doing the tablets. This very strong H2O is within the range of 3200 cm-1 to 3800 cm-1 region. Magnetic susceptibility Diamagnetic If the intensity of magnetization is negative, the material is said to be diamagnetic. This works when the density of lines that force inside the sample is less than that outside in this material. When it placed in an inhomogeneous magnetic field will tend to move to the region of lowest field. The repulsion that forms from the field will then produce energy in it. So, it is an endothermic process. Magnitude of the attractive force increase with the number of unpaired electrons that contain in the transition metal ion. Thus, the complexes that having a single unpaired d electron will interact less strongly with a magnetic field compared with complexes that have two unpaired electrons. So, complexes that contain no unpaired electrons are said to be diamagnetic and it is only weakly repelled by magnetic field. The figure is also very small as order of -1 to -10010-6 c.g.s e.m.u. In addition, it does not depend in the field strength and independent on temperature. In this experiment, th e chloropentaamminecobalt(III) chloride is a diamagnetic compound. The chloropentaamminecobalt(III) chloride has d6 electron configuration that is high spin. It is zero for the unpaired electrons in the orbital.(100) Paramagnetic If the intensity of magnetization of a paramagnetic is positive, hence ÃŽ ´w/ÃŽ ´H is negative and such a material will tend to move regions of maximum field strength since this is an exothermic process. The figure for the paramagnetic susceptibility is large and relative large as fall within the range of 100 to 100,00010-6 c.g.s e.m.u. In addition, it does not depend on magnetic field strength but do depend on temperature. Paramagnetic is a consequence of the interaction of and the spinangular momenta of unpaired electrons with the applied field. Complexes that have no unpaired electron in the orbital will have a magnetic moment that is as strong as it will attract each other stronger in the field. Thus this compound is paramagnetic. In this experiment, the bis(acetylacetonato)oxovanadium(IV) and tris(acetylacetonato)manganese(III) is a paramagnetic compound. The tris(acetylacetonato)manganese(III) has a d4 low spin of electron configuration with twp unpaired electrons. For the bis(acetylacetonato)oxovanadium(IV) has a d3 electron configuration that has 2 unpaired electrons within the orbital. So, this eventually states that both of the products are paramagnetic. (100) The Shape of the Compounds The shape for the bis(acetylacetonato)oxovanadium(IV) is actually in a shape of square pyramidal as I had mention in the introduction. The formation of a square pyramidal complex is due to the ligand that influences it. The steric effect between vanadium and the other oxygen bonding will tend to have competed among each other for the spacing with the other ligands in the metal bonding orbital. This effect can be observed in the decrease in the IR stretching frequency of the VO bond when there is a sixth ligand coordinates trans to oxygen. (9) The shape for penta is in Werner coordination as I have mention also in the introduction. It means that it is in an octahedron shape with a 6 coordination numbers. The ground state for octahedral complexes Mn(acac)3 which is the product of our experiment 1 of is a 5Eg (t2g 3eg1) position. The black manganese(III) acetylacetonate complex that which is the product of our experiment usually has an octahedral configuration. there actually exists of the Jahn teller distortion. Thus, it will be not a pure octahedral conformation. Then, it will have two forms for this compounds where one is with substantial tetrahedral elongation where two Mn-O bonds at 212 pm, and four at 193 pm and the other with moderate tetragonal compression where the two Mn-O bonds at 195 pm and four at 200 pm. Namely, The room temperature effective magnetic moments of the manganese(III) complexes with mixed ligands are in the range of 4.76-4.9 ÃŽ ¼B, which corresponds to four unpaired electrons typical of the d4 system. It is supposed that in mixed-ligand complexes the ligand has localized Ï€-bond and do not favor electron-pairing. The Jahn-Teller effect due to an unequal filling up of t2g and eg orbital yields a distorted octahedral geometry in complex. These complexes have a dark green to green color. The proposed structures of the complexes shown in Fig 3 are consistent with the related data (5).