Presentation on theme: "Molecular Spectroscopic studies of metal(II) [Mn(II), Co(II) and Ni(II)] halogen complexes with methylanilines Part I M. KUMRU, Fatih University, Faculty."— Presentation transcript:
Molecular Spectroscopic studies of metal(II) [Mn(II), Co(II) and Ni(II)] halogen complexes with methylanilines Part I M. KUMRU, Fatih University, Faculty of Arts and Sciences, Department of Physics, Büyükçekmece, Istanbul, TURKEY K. GOLCUK, Dept. of Chem., Univ. of Michigan, 930 N. University, Ann Arbor, MI , USA A. ALTUN, Max Planck Institute, Kaiser-Wilhelm-Platz 1, Mülheim an der Ruhr, GERMANY
Aniline and its derivatives are widely used for producing polyurethanes, rubbers, pesticides and dyes and also found in the environment . Recently, their toxicity effects to Daphnia magna were also studied . Hence, understanding of their molecular properties and the reactions they experience is very important. Besides, their metal(II)halide complexes have been interested for decades [3-9]. As a continuation of our previous works [10-16], we report thermogravimetric (TG) analysis, magnetic moments, electronic spectra and vibrational spectra of the pMA metal(II) [Mn(II), Co(II) or Ni(II)] bromide complexes in the present study. A detailed vibrational band analysis of each metal complex is also given. The spectroscopic investigations are used to obtain the local structure around each metal atoms. Our Related Some Publications : M. Kumru, A. Aypar, Spectrochim. Acta, Vol. 4 7A, No. 12, pp.1789, 1991 M. Kumru, A. Aypar, Doğa- Tr. J. Physics, 16 (1992) M. Kumru, H. Yuksel, A. Aypar, Doğa- Tr. J. Physics, 17(1993) M. Kumru, Fourier Transform Infrared Spectra and Assignment of Vibrations of Hg(3- C 7 H 9 N) 2 Cl 2 and Hg(3-C 7 H 9 N) 2 Cl 2, DOĞA, Turkish Journal of Physics, 19(1995) …………..
A. Altun, K. Golcuk, M. Kumru, " Vibrational and thermal studies of metal(II) [Ni(II), Zn(II) and Cd(II)] iodide m-methylaniline complexes ", Vibrational Spectroscopy, 31(2003) A. Altun, K. Golcuk, M. Kumru, " Theoretical and experimental studies of the vibrational spectra of m-methylaniline", J. Mol. Struct. ( THEOCHEM ), 625(2003)17-24 A. Altun, K. Golcuk, M. Kumru, "Structure and vibrational spectra of p-methylaniline: Hartree- Fock, MP2 and density functional theory studies ", J. Mol. Struct. (THEOCHEM), 637(2003) A. Altun, K. Golcuk, M. Kumru, "Vibrational and thermal studies of p-methylaniline complexes with Ni(II), Zn(II) and Cd(II) iodides", Vibrational Spectroscopy, 33 / 1-2 (2003) 63 –74 K. Golcuk, A. Altun, M. Kumru, "Thermal studies and vibrational analyses of m-methylaniline complexes of Zn(II), Cd(II) and Hg (II) bromides", Spectrochimica Acta, 59A (2003) K. Golcuk, A. Altun, M. Kumru, " Spectroscopic and thermal studies of Mn(II), Co(II) and Ni(II) bromide m-methylaniline complexes ", Journal of Molecular Structure, 657 (2003) K. Golcuk, A. Altun, S. Guner, M. Kumru and B. Aktas, "Thermal, Vibrational and ESR studies of Cu(II) bromide bis(p-methylaniline) and bis(m-methylaniline) complexes" Spectrochimica Acta Part A, 60 (2004) K. Golcuk, A. Altun, M. Kumru, M. Somer " Vibrational and thermal studies of [MBr2(p- methylaniline)2] (M:Zn+2, Cd+2 and Hg+2) complexes", Vibrational Spectroscopy xxx(2005)xxx-xxx
m-methylaniline (mMA) p- methylaniline (pMA) N C H H H C molecular structures
Experimental The ligand (L: pMA) and MBr 2 (M: Mn, Co and Ni) were used as received from Fluka and Aldrich Co. The polycrystalline complexes were prepared using the method given in our previous studies[10-16]. Composition and purity (C, H, N, and M) were determined by microanalysis. Microanalysis data, listed in Table 1, suggest that the complexes have 1:2 (MBr 2 :L) stoichiometry. Therefore, [MBr 2 (pMA) 2 ] form is obtained for all the complexes.
Electronic spectra in EtOH were recorded on a Perkin Elmer Lambda 9 UV-VIS-NIR spectrometer in the range 190–1100 nm. Measurements of magnetic moments at room temperature were made using the Evans method with a Sherwood Sci. magnetic balance. *The molar susceptibilities were corrected for the diamagnetism of the constituent atoms using Pascal’s constants. Thermal analyses were made on a Mettler Toledo TG50 thermobalance under N 2 flow (flow rate, 30 cm3/min). *The samples were heated in an Al 2 O 3 crucible at a rate of 10 C/min.
The cm-1 region FT-IR spectra of the complexes were recorded as KBr discs using a Perkin Elmer Paragon 1000 FT-IR spectrometer. * cm-1 region IR spectra of the complexes were recorded on a Mattson Instruments 2030 Galaxy Series as polyethylene discs at room temperature. The FT-Raman spectra were recorded on a Bruker RFS 100/S FT-Raman Spectrometer in the range 3600 – 70 cm-1. *The 1064 nm line, provided by a 1.5 W Nd:YaG air-cooled laser, was used as excitation line. *A liquid nitrogen cooled Ge detector was used. *The FT-Raman spectra of pMA and its complexes are shown together in Fig. 2.
Vibrational Spectroscopy The only coordination site for the ligand pMA is the nitrogen atom of the amine group. *Hence, we pay attention to –NH 2 group vibrations upon complexation. *The detailed structural and vibrational studies based on ab initio and DFT for free pMA were already discussed in our previous study . *Considering that pMA belongs to C s symmetry point group, the symmetry species (25A + 20A ) of the observed pMA vibrations are given in Table 2 and Table 3. *All observed vibrational bands in the spectra of metal complexes and their assignments are also given in Table 2 and 3. *The FT-IR spectra of pMA and its complexes are given together in Fig. 1.
As an evidence of complex formation between metal(II)bromide and pMA, it is observed that some modes originating from pMA vibrations show substantial shifts in the spectra of complexes. The NH 2 group vibrational frequencies of pMA are much affected by complexation. *This suggests that coordination occur via lone pair electrons of nitrogen. *The hybridization type around nitrogen changes via electron donation from nitrogen orbitals to the metal atom on complex formation [12-16]. *Hence, the N-H bond strength weakens upon coordination and the NH asymmetric and symmetric stretching bands shift toward lower wavenumbers (see Table 1). *The change in HNH angle with coordination decreases scissoring force constant [12-16]. *As a result, the scissoring frequency of the amino group downshifts up to 52 cm -1 upon coordination.
We have assigned the bands observed at 1267 cm–1 (IR) and 1271 cm–1 (Raman) to the CN stretching for free pMA . *The C-N stretching band in the complexes has two components (asymmetric and symmetric stretching of C-N bonds), each of them is observed at lower frequencies compared with the free pMA. *Vibrations of this mode occur at lower frequencies and have two components (asymmetric and symmetric stretching of C-N bonds) in the spectra of complexes, in line with the decrease in the C=N double bond character.
In m-methylaniline (mMA) and p-methylaniline (pMA), the nitrogen atom is out of the ring plane for about 2-3 and the angle between the ring and amino planes reaches to 40 [10,11,17]. *High-level ab initio and DFT calculations, which confirm non-planar geometry of pMA, show that amino group rocking, wagging and twisting vibrations are expected around 1060 cm-1, 600 cm-1 and 250 cm-1, respectively [11,17]. *Hence, we assign the IR band of the free pMA at 1074 cm-1 as the rocking mode. *We could not determine the frequency of the wagging and twisting modes from the experimental IR and Raman spectra of the free pMA due to the broadness or low intensity of the bands.
In the complexes, amino group rocking, wagging and twisting vibrations shift towards upper frequencies. *The rocking vibration has been observed in the complexes around cm-1. *The wagging mode shifts upon coordination to cm-1 region and appears as a strong and coordination sensitive band . *A study of normal coordinate analysis on aniline was reported and the band at 216 cm-1 in IR spectrum of aniline was assigned to NH2 twisting mode. *On the other hand, this band was found at 605 cm-1 in aniline-Cd complex . *Therefore, we assign the cm-1 region bands of the complexes, as the NH2 twisting vibrations, which are not observed in the spectra of free pMA. *The explicit metal-sensitivity can be explained directly by mechanical coupling of this mode with M–N vibrations [14-16].
The metal-ligand bands are helpful for determining the local structure around metal ions. *It is considered that the metal-ligand vibrations occur below 500 cm–1 [3-16]. *Assignments of the (M-N) and (M-Br) vibrations, listed in Table 3, have been given carefully by considering the internal modes of mMA and comparing with literature reports [3-16]. *The cm–1 region IR spectra of the complexes are shown together in Fig 3. The metal-ligand bands are helpful for determining the local structure around metal ions. *It is considered that the metal-ligand vibrations occur below 500 cm–1 [3-16]. *Assignments of the (M-N) and (M-Br) vibrations, listed in Table 3, have been given carefully by considering the internal modes of mMA and comparing with literature reports [3-16]. *The cm–1 region IR spectra of the complexes are shown together in Fig 3. For the Co (II) complex, strong and medium IR bands at 420 cm–1 and 394 cm–1 were assigned to (Co-N) stretching vibrations. *We observed terminal Co-Br bond stretching, i.e. (Co-Br)t bands at 217 cm–1 and 208 cm–1 . *In Co(II) complex, the metal ion is involved in a tetrahedral N2CoBr2 skeleton. *Assuming C2v symmetry for this complex, both the asymmetric and symmetric CoBr2 and CoN2 stretching vibrations are IR active . *Then, the (Co-Br)t and (Co-N) stretching vibrations can be described with A1+B1 and A1+B2 representations, respectively. *Thus, the metal-ligand vibrational bands are consistent with previously reported tetrahedral Co(II) complexes [3-6,14,19].
The stretching vibrations of the bridging M-Br-M bonds, i.e. (M- Br)b, should appear below 200 cm–1 [14,20]. *In Raman spectrum of Mn(II) complex (see Fig.2(c)), we could not observe (Mn-Br)b, bands due to broad strong Raman band around 100 cm–1 which is ascribed as the lattice mode of the solid complexes  and couple with torsional mode of CH 3. In FT-Raman spectrum of Ni(II) complex (see Fig.3(d)), the 155 cm–1 and 136 cm–1 bands are due to the stretching bands of bridging Ni-Br-Ni bonds, i.e. (Ni-Br)b. *Hence, the appearance of the (Ni-Br)b vibrations indicates a polymeric octahedral structure around metal ions with exclusively bridging bromides for [NiBr 2 (pMA) 2 ] complex. *On the other hand, the nonappearance of (Mn-Br)t bands can be concluded that the local environment of Mn ion consists of polymeric octahedral structure, as also proposed for [MnBr 2 (mMA) 2 ] complex . ****As a result, each of Mn and Ni ions is surrounded by four bromine atoms and two nitrogen atoms of the ligands, having a polymeric octahedral structure [3,5,8,14,19].
The coordination number effect on metal-ligand vibration frequencies is known to be a substantial one [4,14]. *Substitution of Ni(II) by Co(II) causes to a decrease in (M-N). Substitution of Co(II) by Mn(II) is expected to lead to an increase in (M-N). *This result arises from the bonding capacity of the metal ion being distributed over more bands with consequently lower metal-ligand force constants [4,14]. *If the coordination number remains unchanged, (M-N) bands follow the sequence Mn
"name": "The coordination number effect on metal-ligand vibration frequencies is known to be a substantial one [4,14].",
"description": "*Substitution of Ni(II) by Co(II) causes to a decrease in (M-N). Substitution of Co(II) by Mn(II) is expected to lead to an increase in (M-N). *This result arises from the bonding capacity of the metal ion being distributed over more bands with consequently lower metal-ligand force constants [4,14]. *If the coordination number remains unchanged, (M-N) bands follow the sequence Mn
(pMA)[MnBr 2 (pMA) 2 ][CoBr 2 (pMA) 2 ][NiBr 2 (pMA) 2 ] IRRaIRRamanIRRamanIRRaman Sym metry Assignments 3416 s3418 w3293 s 3276 s 3311 m3312 s AA NH asym 3333 s3337 w3238 vs3244 s 3226 vs 3227 m3240 s3232 vs A NH sym 3220 m3224 w3123 m 3124 m 3121 w3120 w,br2 x 1621 overton 3056 w3054 s3054 vw3054 s 3054 vw 3057 s3065 vw3057 vs A CH ring 3020m, sh 3032 s3031 m3030 s 3031 m 3032 m3032 w3038 s,sh AA CH ring 3008 m3013 s3011 s3012 m3008 w3014 s AA CH ring 2912 m2917 s2920 m2916 m 2925 m 2924 s2911 m2915 vs A CH 3 sym 2859 m2861m2868 w2863 m 2864 vw 2860 w2857 m2864 vs2 x 1458 overton 2737 w2738 w2731 vw2722 w2721 w2735 w2 x 1380 overton 1621 vs1617 s1573 s1575 m,sh 1578 vs 1576 w1569 vs A NH 2 sciss s1621 s 1612 w,sh 1612 s1615 s1616 vs A CC ring 1582 s, sh 1581 m1596 s1595 m AA CC ring 1514 vs1518 vs1519 m 1512 vs 1516 vs1518 w A CC ring 1458 w1451 w 1455 w 1451 m,br1449 w AA CH 3 asym 1441 s1440 w,br 1430 vw,br AA CC ring 1380 m1374 w1380 s 1380 vw 1379 m1379 w1377 m A CH 3 sym 1324 m1324 w1317 m1324 m1327 vw1326 vw1327 w AA CH ring 1281 m1294 m1295 w1292vw,1296 w1293 w AA CC Table 2. Infrared and Raman frequencies of pMA and metal comlexes
(4-MA)[MnBr 2 (4-MA) 2 ][CoBr 2 (4-MA) 2 ][NiBr 2 (4-MA) 2 ] IRRaIRRamanIRRamanIRRamanSimBant Tanımları 1281 m1243 vs1237 m1238 m1250 s1242 s A CN 1216 s1222 s s1222 vs CN 1218 m1205 m1204 s1217 w1207 w,sh1207 vs A CCH s1179 m1160 m1183 s1181 m1180 m1179 s A CH ring 1120 s1100 s, sh1116 w,sh1123 w,br AA CH ring 1074 m 1070 vs1080 vs1062 vs1070 w,sh AA NH 2 rock vs1065 s vs A NH 2 wag. 983 w998 m s1000 s A CCC ring 953 w956 w650 vw960 vw,sh AA CH 3 ; CCH 3 ; CCC 931 w936 w932 vw938 s830 vw A CH ring; CCC ring 844 s836 m837 s841 s837 s835 m830 vs A CCC ring; CN 812 vs 810 vs813 s810 m A CH ring; CCC ring 806 vs 809 m810 vs AA CH ring; CCC ring 720 m739 s743 w741 s739 w733 s742 m A Breathing 702 s702 vw707 m705 w705 s709 vw A CCC ring 645 s661 s660 s649 s645 m647 s650 vw AA CCC ring 566 s556 m634 s635 m607 vs610 m AA NH 2 twist. 504 vs 510 vs521 w507 s524 m523 vs518 vw A CCC ring
4-MA[MnBr 2 (4-MA) 2 ][CoBr 2 (4-MA) 2 ][NiBr 2 (4-MA) 2 ] IRRaIRRamanIRRamanIRRamanSimetriBant Tanımları s 474 s472 m472 vs476 m A CCC ring 406 m405 m420 s421 m412 m410 m (M-N) 361 m m395 w386 m (M-N) 335 m300 s307s303 s299 vs308 s315 w A CCH 3 ; CCC; CN 297 s285 vs 278 w vw273 m,sh AA CN; CCH s227 m234 mNMN deformation s213 s (M-Br) t 208 s211 vs (M-Br) t 155 vs (M-Br) b Table 2. (Continued) Key :, stretching; , in-plane deformation; , out-of-plane deformation; s, strong; vs, very strong; m, medium; w, weak; vw, very weak; sh, shoulder; br, broad.
FT- Raman spectra of (a) [MnBr 2 (3-MA) 2 ] and (b) [NiBr 2 (3-MA) 2 ] complexes
FT-Raman spectra of (a) [MnBr 2 (4-MA) 2 ] and (b) [NiBr 2 (4-MA) 2 ] complexes
FT-Raman spectra of (a) [CoBr 2 (4-MA) 2 ] and (b) [CoBr 2 (3-MA) 2 ] complexes
IR spectra of (a) [NiBr 2 (3-MA) 2 ], (b) [MnBr 2 (3-MA) 2 ] and (c) [CoBr 2 (3-MA) 2 ] complexes in the range of 500–200 cm –1
IR spectra of (a) [NiBr 2 (4-MA) 2 ], (b) [MnBr 2 (4-MA) 2 ] and (c) [CoBr 2 (4-MA) 2 ] complexes in the range of 500–200 cm–1
Electronic (UV-VIS) Spectroscopy The electronic spectral data and magnetic moment values of the complexes are given in Table 4. *The UV- vis spectrum of [MnBr2(pMA)2] complex gives only one band around cm–1. *This band corresponds to 6A1g(S) → 4A1g(G), 4Eg(G) spin forbidden d-d transition. *The spectrum band and the value of magnetic moment ( eff = 5.56 B.M.) are consistent with those predicted six coordinated polymeric octahedral Mn(II) complexes [5,14,19]. *The magnetic moment value of the complex is lower than spin-only value of a Mn(II) ion, showing Mn-Mn interaction .
The electronic absorption spectrum of [CoBr 2 (pMA) 2 ] complex shows some overlapping bands at cm-1, cm-1, cm-1 and cm-1. *The band at cm-1 arises from spin allowed 4A2(F) → 4T1(P) electronic transition. *The bands at cm-1, cm–1 and cm–1 are due to spin forbidden transitions and assignable to 4A2(F) → 2E(G), 4A2(F) → 2T1(G) and 4A2(F) → 2T2(G), respectively, indicating fine structures due to pseudo-tetrahedral structure. Magnetic moment value was found as 4.72 B.M. and consistent with high spin tetrahedral Co(II) complexes [14,23,24]. *Therefore, the proposed tetrahedral structure consists of N 2 CoBr 2 coordination sphere.
In the UV-vis spectrum of [NiBr 2 (pMA) 2 ] complex, two bands were observed at cm–1 and cm–1. The absorption band at cm–1 arises from 3A2g(F) → 3T1g(F) transition, while the absorption band at cm–1 corresponds to 3A2g(F)→ 3T1g(P) transition. *The positions of the d-d transitions indicate that the Ni ion is in a polymeric octahedral environment with bridging bromides . *The magnetic moment value ( eff = 3.15 B.M.) of the complex, which shows the presence of two unpaired electrons, lies in the region expected for octahedral Ni complexes .
Electronic transitions Transition Mulliken representation (nm ) * *N V <200 * *N V 200–500 n *N Q 160–260 n *N Q 250–600
UV- VIS spectrum of pMA 291 nm de görülen bant n→ *, 237 nm de görülen bant → * 207 nm de görülen bant ise n→ * geçişlerine karşılık gelmektedir. UV- VIS spectrum of mMA. 287 nm de görülen bant n→ *, 237 nm de görülen bant → * ve 203 nm de görülen bant ise n→ * geçişlerini göstermektedir.
Electronic Transitions of Transition metal complexes Geçiş metal komplekslerinin soğurmaları genellikle dolu olmayan d orbitallerine geçişlerden veya yük transferi geçişlerinden kaynaklanmaktadır. Serbest iyondaki d orbitallerinin (a) oktahedral ve (b) tetrahedral alanda yarılmalarıyla meydana gelen enerji-seviye diyagramları
420 nm de bir soğurma bandı gözlenmiştir. Bu soğurma, elektronun 6 A 1g (S) → 4 T 2g (G) enerji seviyeleri arasındaki spin yasaklı geçişinden kaynaklanmaktadır. UV-VIS spectrum of [MnBr 2 (4-MA) 2 ] 412 nm görülen band 6 A 1g (S) → 4 A 1g (G), spin yasaklı geçişine ve 546 nm görülen band ise 6 A 1g (S) → 4 T 1g (G) spin yasaklı geçişine karşılık gelmektedir. UV-VIS spectrum of [MnBr 2 (3-MA) 2 ]
UV-VIS spectra of (a) [CoBr 2 (4-MA) 2 ] and (b) [CoBr 2 (3-MA) 2 ] complexes. 670 nm gözlenen bantlar 4 A 2 (F) → 4 T 1 (P) geçişine karşılık gelmektedir. 640 nm, 622 nm ve 590 nm de görülen omuzlar Co(II) metali etrafında meydana gelen pseudo-tetrahedral (tetrahedralimsi) yapının bir sonucudur. Ayrıca ortaya çıkan bu ince yapılar spin yasaklı geçişlerin de bir sonucu olup; 4 A 2 (F) temel seviyesinden 2 E(G), 2 T 1 (G) ve 2 T 2 (G) seviyelerine olan geçişleri göstermektedir.
UV-VIS spectra of (a) [NiBr 2 (3-MA) 2 ] and (b) [NiBr 2 (4-MA) 2 ] complexes 780 nm de gözlenen band 3 A 2g (F) → 3 T 1g (F) elektronik geçişini, 420 nm deki bant ise 3 A 2g (F) → 3 T 1g (P) elektronik geçişini gösterir.
Complexes max (nm) Electronic Transitions [MnBr 2 (4-MA) 2 ]420 6 A 1g (S) → 4 A 1g (G) [MnBr 2 (3-MA) 2 ]412 6 A 1g (S) → 4 A 1g (G) A 1g (S) → 4 T 1g (G) [CoBr 2 (4-MA) 2 ]340CT A 2 (F) → 2 T 2 (G) A 2 (F) → 2 T 1 (G) A 2 (F) → 2 E(G) A 2 (F) → 4 T 1 (P) [CoBr 2 (3-MA) 2 ]340CT A 2 (F) → 2 T 2 (G) A 2 (F) → 2 T 1 (G) A 2 (F) → 2 E(G) A 2 (F) → 4 T 1 (P) [NiBr 2 (4-MA) 2 ]420 3 A 2g (F) → 3 T 1g (F) A 2g (F)→ 3 T 1g (P) [NiBr 2 (3-MA) 2 ]420 3 A 2g (F) → 3 T 1g (F) A 2g (F)→ 3 T 1g (P) Electronic absorption spectrum results of complexes
Thermal analyses Thermal decomposition data of the metal complexes are listed in Table 5. *As an example, TG and DTG traces for [MnBr2(pMA)2] complex are shown in Fig. 4. *In the TG-DTG curves of Mn(II) complex no weight changes are observed until 103 C, where an initial weight loss is observed. In the temperatures between 226 C and 290 C, the rest of the pMA is removed immediately from the complex, leaving the intermediate MnBr2. *The metal salt starts to decompose at 295 C. *The residual weight is in good agreement with the value required for MnO.
The Co(II) and Ni(II) complexes decompose in a two-step mass loss reaction. *The first step ( C range) for the Co(II) complex corresponds to the loss of 2 moles of pMA. *The second decomposition stage registered between C matches the decomposition of CoBr 2 finally to CoO. *The Ni(II) complex loses 2 moles of pMA in C temperature. *The observed weight losses for the decomposition processes in each of the compounds compare favorably with the theoretical values listed in Table 5.
Experimental Parameters [MnBr 2 (3- MA) 2 ] [MnBr 2 (4- MA) 2 ] [CoBr 2 (3- MA) 2 ] [CoBr 2 (4- MA) 2 ] [NiBr 2 (3- MA) 2 ] [NiBr 2 (4- MA) 2 ] [CuBr 2 (3- MA) 2 ] [CuBr 2 (4- MA) 2 ] m (g)0,05750,09850,08500,07880,10790,13900,07050,0601 L (cm)22,52,32,52,42,52,32,2 RdRd RbRb M w (gmol –1 )429,05 433,05 432,81 437,66 g x ,184330,043120,898820,85669,27639,02971,96302,1570 m x ,808712,88999,05029,03194,01493,90810,85910,9443 d x ,64 A x ,041312,89019,28289,26454,24754,14071,09181,1769 T (K)298 eff (BM) 5,805,564,734,723,203,151,621,68 n Spin states High spin High spin High spin High spin Magnetic succeptibility results of complexes
Termogravimetrik Analiz Sonuçları Termal analizler Mettler Toledo TG50 termobalansı kullanılarak, 35–900 C aralığında, 30 cm 3 /dak. lık akış hızına sahip N 2 dinamik atmosfer gazı altında yapılmıştır. Toz haldeki numunelerden yaklaşık 10 mg civarında alınarak, 70 l lik standart alüminyum oksit (Al 2 O 3 ) kaplar içinde 10 C/dak. lık ısıtılma oranına sahip termobalansa yerleştirilmiştir. Her bir numune için TG eğrilerinin yanında kısmen örtüşmüş termal ayrışma reaksiyonlarını ortaya çıkarmak ve sonuçları daha iyi yorumlayabilmek için DTG eğrileri de kaydedilmiştir. Böylece bu sıcaklıklar arasında numunede meydana gelen termal ayrışma reaksiyonları ortaya konularak her bir numunenin termal karakterizasyonu yapılmıştır.
TG-DTG curvers for [CoBr 2 (3-MA) 2 ] TG-DTG curves for [CoBr 2 (4-MA) 2 ]
TG-DTG curves for [NiBr 2 (3- MA) 2 ] TG-DTG curves for [NiBr 2 (4- MA) 2 ]
TG-DTG curves for [MnBr 2 (4- MA) 2 ]
TG-DTG curves for 4-MA TG-DTG curves For 3-MA
Conclusion The spectroscopic studies of [MnBr 2 (pMA) 2 ], [CoBr 2 (pMA) 2 ] and [NiBr 2 (pMA) 2 ] complexes show that metal-ligand coordination occurs via nitrogen atom of the pMA. *The vibrational spectra reveal the type of the coordination around each metal ion. *The information referring to the geometry of the studied complexes is also obtained from the electronic spectra and from the values of magnetic moments. *The spectroscopic and magnetic data suggest that the Co(II) complex has a tetrahedral structure, with the cobalt ion bonded to two bromide ions and two nitrogen atoms from two different pMA ligand, while the Mn(II) and Ni(II) complexes have the metal ions in a polymeric octahedral environment with bridging bromides.
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Tetrahedral Co(II) kompleksleri metal iyonu etrafında lokal olarak C 2v simetrisine sahiptir. CoBr 2 ve CoN 2 antisimetrik ve simetrik gerilmeleri IR aktif ve Raman aktiftir. Co(II) komplekslerinin 420–399 cm –1 deki IR bantları (Co-N) gerilmelerinden, 230– 210 cm –1 de görülen bantları da terminal Co–Br bağ gerilme titreşimlerinden kaynaklanmaktadır. Cu(II) komplekslerinin titreşim spektrumlarında sırasıyla cm –1 ve 202–207 cm –1 aralığında gözlenen terminal Cu–Br antisimetrik ve simetrik bağ gerilemeleri metal atomu etrafındaki tetragonal yapıyı gösterir. 200 cm –1 in altında gözlenen bantlar eksenel zayıf Cu-Br etkileşimlerinden kaynaklanmaktadır. Cu(II) kompleksleri için metal atomu etrafındaki muhtemel yapı yandaki şekilde verilmektedir. (N: 3-MA veya 4- MA nın azot atomu; noktalı çizgi zayıf Cu-Br etkileşmesini temsil eder). Br –z Br –z +z Cu N N Br –z +z Cu N N
Zn(II) kompleksleri için metal–ligand ve terminal metal–bromür titreşimleri tetrahedral bir çevre için öngörülen değerlerde çıkmaktadır. Buna göre Zn(II) kompleksleri, N 2 ZnBr 2 koordinasyon küresiyle C 2v simetrisine sahip tetrahedral bir çevrede bulunmaktadır. Cd(II) ve Hg(II) komplekslerinin titreşim spektrumlarında (uzak-IR ve Raman) 200 cm –1 in üzerinde görülen bantlar terminal Cd–Br ve Hg–Br bağ gerilmesine ve 200 cm –1 altında ortaya çıkan bantlar (Hg-Br) b titreşimlerine karşılık gelir. Buna göre kompleksler 5-koordinatlı dinükleer yapılardan veya bir tane terminal M–Br bağına sahip brom köprülü 5-koordinatlı polimerik yapılardan meydana gelmektedir. Cd(II) ve Hg (II) kompleksleri için metal atomu etrafındaki muhtemel yapı yandaki şekilde verilmektedir. (M: Hg veya Cd; Br’: köprü yapmış Br atomu; N: 3-MA veya 4-MA nın azot atomu). Br Br’ Br N N N N MM