Synthesis and spectral studies on mononuclear complexes of chromium(III) and manganese(II) with 12-membered tetradentate N2O2, N2S2 and N4 donor macrocyclic ligands

Transition Metal Chemistry 29: 269–275, 2004. Ó 2004 Kluwer Academic Publishers. Printed in the Netherlands.269 Synthesis and spectral studies on mononuclear complexes of chromium(III) and manganese(II) with 12-membered tetradentate N2O2, N2S2 and N4 donor macrocyclic ligands Sulekh Chandra* and Rajiv Kumar Department of Chemistry, Zakir Husain College, University of Delhi, Jawaharlal Nehru Marg, New Delhi 110002, India Received 15 July 2003; accepted 02 September 2003 Abstract Complexes of CrIII and MnII of general formula [Cr(L)X2] X and [Mn(L)X2] respectively were prepared from N2O2, N2S2 and N4 donor macrocyclic ligands. The complexes have been characterized by elemental analysis, molar conductance measurements, spectral methods (i.r, mass, 1H-n.m.r, electronic spectra and e.p.r.) and magnetic measurements. The macrocyclic ligands have three different donating atom cavities, one with two unsaturated nitrogens and the other two have saturated nitrogen, oxygen and sulphur atoms. The effect of different donor atoms on the spectra and ligand field parameters is discussed. All the complexes show magnetic moments corresponding to a high-spin configuration. On the basis of spectral studies a six coordinated octahedral geometry may be assigned to these complexes. Introduction Enormous progress in macrocyclic chemistry has been made in the past decade [1, 2]. New macrocyclic ligand molecules have been designed and prepared with enhanced ability to encapsulate given metal ions selectively [3, 4]. Coordinated metal ions influence the course of many complicated reactions occurring during metabolic activity in living organisms [5]. The coordination chemistry of manganese has achieved remarkable progress in the last decade due to the increased recognition of this metal’s role in biological systems [6, 7]. In this paper we report the synthesis and characterization of chromium(III) and manganese(II) complexes with N2O2, N2S2 and N4 donor macrocyclic ligands viz 2,3-diphenyl-1,4-diaza,7,10 dioxo,5,6:11,12-dibenzo [e,k]-cyclododeca-1,3 diene[N2O2] ane (L1), (Figure 1) 2,3-diphenyl-1,4,7,10-tetraaza-5,6:11,12-dibenzo [e,k]cyclododeca 1,3 diene [N4] ane (L2) (Figure 2) and 2, 3-diphenyl-1,4-diaza,7,10-dithia,5,6:11,12-dibenzo [e,k]cyclododeca-1,3 diene [N2S2] ane [L3] (Figure 3) containing aromatic head, and lateral units [8, 9]. An important aspect of the present work is the synthesis of three novel dibenzo-substituted Schiff-base macrocycles derived from three different diamines containing aromatic rings with different donating atoms. Experimental All starting materials used were of analar grade, were purchased from Sigma Aldrich, and were used as received. * Author for correspondence Physical measurements Magnetic susceptibility measurements were carried out on a CAHN 2000 Faraday balance using Hg[Co(CNS)4] (vg ¼ 16.44 · 10)6 g cc)1 at 28 °C) as the calibrating agent. Molar conductance measurements were carried out on a Leeds Northrup Conductivity Bridge 4995. I.r. spectra were recorded on a Perkin Elmer 137 instrument as KBr pellets. The electronic spectra of the complexes were recorded on a Shimadzu u.v. mini-1240 spectrophotometer in DMF solution. C and H analysis were carried out on a Carlo-Ebra 1106 elemental analyzer. Nitrogen was determined by Kjeldahl’s method. Mass spectra were carried out on JEOL, JMX, DX-303 mass spectrophotometers. 1H-n.m.r. spectra were recorded on a Bruker AVANCE 300 spectrometer at 100 kHz modulation at room temperature. E.p.r. spectra were recorded at room temperature on a Varion E-4 EPR spectrometer at ca. 9.1 GHz and 100 kHz field modulation and phase sensitive detections and DPPH was used as marker. The macrocyclic ligands were prepared in three steps. Nitro compounds (Scheme 1) (a) 1,2-Di(o-nitrophenoxy)ethane o-NO2C6H4OH (4.78 g) in hot DMF (5.0 cm3) was treated slowly with K2CO3 (2.39 g). The resulting solution was boiled gently and BrCH2CH2Br (1.54 cm3) was added dropwise with constant stirring for 30 min. The mixture was then refluxed gently for 2 h and concentrated under reduced pressure. On pouring the solution into cold water a granular yellow solid precipitated. It m). Structures of microcyclic ligands. m).1 (2H. m. The mixture was then cooled and poured into H2O (300 cm3).2-di(onitrophenylamino)ethane (3. The product was recrystallized from EtOH. d). (b) 1. were heated under a N2 atmosphere with 5% PdAC (0.m. Fig.372 cm3) in EtOH (1 cm3) was then added dropwise with constant stirring to the refluxing solution.0 cm3). The reactions are given below (Figures 6 and 7). Reduction of nitro compounds (Schemes 2a and b) The nitro products.p. 75 °C. d). N2H4 Æ H2O (20. A residue of white plates was obtained. 2. d 7.6 (2H.0 (H. d 4. Ligand (L2 ). d 7.6 (2H.r.2-Di(o-aminophenylthio)ethane (Scheme 3) This diamine was prepared by heating o-HSC6H4NH2 (1. d 7. m.0 (4H.3 (2H. d 3.1 g) as bright orange needle shaped crystals.p.2-di(o-nitrophenoxy)ethane and 1.: (CDCl3) d 6. Fig. C6H6 (30.1 (2H. 1.1 (2H.m.2-Di(o-nitrophenylamino)ethane (Scheme 2) 1. dried and recystallized from glacial MeCO2H. d 4. m.H2NCH2CH2NH2 (0. m). d 7. Fig. d 7.3 (2H.: (CDCl3) d 6.2. The reaction is given below (Figure 8).0 (2H. The mixture was stirred rigorously until Fig.3 (2H. OACH2). 1H-n.2. 4.r.m.p. d 7.7 (2H.p. was filtered. Fig. the solid so obtained was washed with a mixture of Et2O (30. OACH2) diamine(I) and 135–136 °C. NHACH2). 1. 1H-n. d). 3.r. Ligand (L3 ).2-Di(o-introphenoxy)ethane (Scheme 1).26 cm3). d). 1H-n. 192–194 °C. d).: (CDCl3) d 8. 1.0 g) with 1.di(o-nitrophenylamino)ethane. was filtered washed with H2O and dried.2-Di(o-nitrophenylamino)ethane was prepared by heating BrC6H4NO2 (2. 1.0 cm3) and 1 N NaOMe solution (10 cm3).0 cm3) was added in (5 cm3) portions and the mixture refluxed until the solution become colourless (30 min).0 (4H. BrCH2CH2Br (0. m). m. d). d). NHACH2) diamine(II). 169– 170 °C.r. washed with dilute aqueous NaOH. 1. d 7.2 (2H. The heating was then reduced to keep the mass molten for a further use.m.201 g). d 6.3 (2H.0 (4H. m). It was recrystallized from ClCH2CH2Cl to give 1. 5. d).6 (2H. . m).r. The reaction is given below (Figure 4).0 (4H.1 (2H.1 (2H. After filtration to remove the precipitate (if any). d).270 complete reaction had occurred.8 (4H. d). d 7. the solution was evaporated to dryness and the solid residue recrystallized from hot EtOH under a N2 atmosphere. The reaction is given below (Figure 5).5 g).: (CDCl3) d 8. d 2. m).: (CDCl3) d 6. m. 1H-n.0 cm3).7 (2H. The melt was poured into EtOH (50. m). d). The solid mass so obtained. m). d 6. 130–132 °C. 1H-n. m.0 (H.3 (2H.2-Di(o-introphenylamino)ethane (Scheme 2). d 7. Ligand (L1 ).m. d 6. d 4. SACH2).09 g) with absolute (99%) EtOH (3 cm3) containing Na (0.7 (2H. d 7. d 7. d 6. and a yellowish residue was obtained. spectra of macrocyclic ligands Fig. m). The white/white off crystals which formed were filtered.27 (2H. d 7.r.1 (L2) C28H24N4 calcd. m.1.6 (2H.9 (2H. m). d). m). 291 (15). d 7. 6. N.6. 4.: C.10dithia. H.: C. 6).05 mol.3.2–7. 1H-n. 4.0 (L3) C28H22N2S2 calcd.: C.4%. (Yield: 71%).1 (2H. Ligand (L3): d 7. 2.2.2-di(o-nitrophenoxy)ethane Fig. To an EtOH solution (25 cm3) of benzyl (0. H.9 (2H. Found: C.4.2-di(o-aminophenylamino)ethane or 1. d) d 4.0 (4H.r. d 6. 222 (50). 58 (35).2-di(o-aminophenoxy)ethane or 1. Fig. d) d 3.m. N. H. 6.10-tetraaza-5.10-dioxo.05 g).0 (2H. EIMS m/z (%) 415 (M+. mass spectra. m). 85 (100). N.9 (2H.0 (4H.4 (10H.3-diphenyl-1.5. d 7. 80.12-dibenzo [e.k]-cyclododeca-1. 1. 179 °C for ligand (L2) and (yield: 70%) m.6:11.p.k]-cyclododeca 1. OACH2). 182 °C ligand (L3).12-dibenzo [e.2-Di(o-aminophenoxy)ethane (Scheme 2b). 80.6:11.p. (Found: C.1 (2H.7%. 219 (19). d).4. 6. d 6. 147 (40). 60).2-di(o-nitrophenylamino)ethane reduced pressure and kept overnight.7. d 6.m. 3 diene[N2O2] ane (L1). 13. Reaction mechanism of macrocyclic ligands. N. 77 (62). 5. d 6.0.3-diphenyl-1.9. 5.12-dibenzo [e. Macrocyclic ligands 2. (II) Reduction of 1. 1.7. 6.3. EIMS m/z (%) 417 (M+. Mass spectrum. m. H. washed with EtOH and dried under vacuum over P4O10. and i. d 7. 80.7.3 (10H.4-diaza.24 (10H. an EtOH solution (25 cm3) of 1.3 diene [N4] ane (L2) and 2. d 6. d 6. 74. The mass spectrum of the ligand (L1) shows a peak at 417 amu. Found: C. 5. 192 (80). Mass spectrum.6 (2H. m). N. 105 (90).3 diene [N2S2] ane [L3] were obtained as described below. m).2–7. These ligands were characterized by elemental analysis. 8. Ligand (L2): d 7.7 (2H. 6. N.3. m). 80.7. 1. NHACH2). 350 (30).2%) Figure 9.p. m.2-di(o-aminophenylthio)ethane (0.r. d 7. 9. H. The solution was then concentrated to half its volume under Fig. 275 (20).005 mol) was added in the presence of a few drops of conc. spectra.4-diaza. m). 1 H-n. Ligand (L1): d 7. d 6. The mass spectrum of the ligand (L2) shows a peak at 415 amu.2-Di(o-aminophenylthio)ethane (Scheme 3).3-Diphenyl-1.271 (I) Reduction of 1.k]-cyclododeca-1.5. 13. .6:11. 7.8.1.1 (2H. corresponding to the molecular ion (M++1).0. m). 172 °C ligand (L1) (yield: 67%). HCl and the resulting solution boiled under reflux for 5–7 h. d). corresponding to the molecular ion (M++1). 5.2–7. d) d 4.0 (4H.. 1. 376 (4). 76. H. (L1) C28H22N2O2 calcd.6 (2H.2-Di(o-aminophenoxy)ethane (Scheme 2a). 4.6) 3.8) 61. This indicates diversion of the electron cloud from the nitrogen of the imidazole or amino group.6 (61.6:11.2 (3.0 85.0 (4. On complexation this band is shifted towards the lower side 3310 cm)1.85 (62.272 SACH2). L2 and L3 PhAOACH2. This moderate intensity absorption band is showing a shift to the lower side in the complexes.15) 9.8 (10. It confirms the elimination of water molecules and. A new band appeared in the 310– 490 cm)1 range in the spectra of chromium(III) and manganese(II) complexes. 1755 cm)1 shows the absence of ketonic groups.4-diaza. 370 (35). EIMS m/z (%) 449 (M+. spectra of L1.1) H 2.3 diene[N2O2] ane(L1).5.8 (5.3 diene [N4]ane (L2) and 2. In the i.0) 8. as a result. corresponding to molecular ion (M++1). I.0 light green light green blackish green pale yellow yellow pale yellow yellow off white white 8.9 (4.0 (47. whereas the manganese(II) complexes are non-electrolytes (Table 1). The i.3 (7. 52)..0 16. L2 and L3 and X ¼ Cl) or SCN)).8) 3.7.3-Diphenyl-1.3) 47.8) 4. Chromium(III) complexes show molar conductances corresponding to 1:1 electrolytes. (°C) Molar conductance (W)1 cm2 mol)1) Colour Found (Calcd) (%) M [Cr(L1)Cl2] Cl Cr C28H22N2O2 Cl3 [Cr(L2)Cl2] Cl Cr C28H24N4 Cl3 [Cr(L3)Cl2] Cl Cr C28H22N2 S2 Cl3 [Mn(L1)Cl2] Mn C28H22N2O2Cl2 [Mn(L1)(SCN)2] MnC30H22N4O2S2 [Mn(L2)Cl2] Mn C28H24N4Cl2 [Mn(L2)(SCN)2] MnC30H24N6S2 [Mn(L3)Cl2] Mn C28H22N2 S2Cl2 [Mn(L3)(SCN)2] MnC30H22N4S4 40 45 63 60 50 65 61 68 62 206 200 190 175 180 190 195 180 189 95.3 diene[N2S2]ane [L3]. Mass spectrum.0 18.0 (61.2 (14.1 (3.1 (9. spectra of these complexes show a moderate intensity absorption in the 1590–1610 cm)1 range attributed to the imine.k]-cyclododeca-1. In the i.5) 4.0 (61.005 mol) (where ) X ¼ Cl . 2. or SCN)) was added to a hot EtOH solution 3 (20 cm ) of the corresponding ligand (0.85 (9.10 dioxo.8 (58.0 (8. suggesting coordination through the nitrogen of the m(C@N) group.16) 4.10-tetraaza-5.0) 7.6:11.7.1 (4.1) 2.9 (10.8 (10. spectra The absence of an absorption at ca. spectra of L1 (1624 cm)1). m(C@N). 185 (81).0) 61.p. PhANHACH2 and PhASACH2 group show bands in the 305–485 cm)1 range. cyclization takes places with formation of a macrocyclic ligand.75) 4. solution (20 cm3) of the hydrated metal salts.4-diaza.3-diphenyl-1.3) 9.3 (4.0 11.10-dithia.r.8) 3. 12].7.r. The mixture was then refluxed on a water bath at 80 °C for 5–7 h.2) N 4.r. Results and discussion All the complexes have compositions CrLX3 or MnLX2 (L ¼ ligands L1.k]-cyclododeca-1. spectra also confirmed the MACl band in the range 300– 320 cm)1 consistent with coordination of the halo group.0 12.k]-cyclododeca 1.15 (9.005 mol). .3) 14.1 (4. 250 (25). On cooling a precipitate was obtained which was filtered. These bands are also shifted to the lower side after complexation of the macrocyclic ligands and confirm the complexation of the macrocyclic ligands.3) 57.0) 8.5) 9.2) 61. These weak bands can be assigned to 405 cm)1 m(MAO). Far i. and the absence of a strong band at ca.5.1) 8. L2 (1620 cm)1) and L3 (1608 cm)1) a new band appears in all the ligands corresponding the m(C@N) group. The mass spectrum of ligand (L3) shows a peak 449 amu.1 (9. bands of all complexes are recorded in Table 2. 1675– Table 1.0 (9.6) C 57.12-dibenzo [e.9 (3. 421 (71). The complexes may therefore be formulated as [CrLX2] X and [MnLX2] respectively.12-dibenzo[e.25 (9.5 (8. CrX3 Æ xH2O or MnX2 Æ xH2O (0.1) 3.r.r. Important i.9 (4.9 (58.6:11. washed with EtOH and dried over P4O10 under vacuum. The spectrum of ligand (L2) shows a band at 3320 cm)1 corresponding to m(NH) [10].1) 61. Preparation of complexes A hot EtOH.85) 9.5) 9.5) 8.0 4.4 (4.r.0 (3.0 15.9) 9. 3400 cm)1 in the i.2) 3.15 (58.9 (55. 51 (38).0 98. 402 (15). Related data are listed in Table 1.1) 9.6 (8.3) 58.9) 9. Characterization data for the CrIII and MnII complexes Complex Yield (%) M. thus resulting in a lowering of the NAH stretching frequency. spectra of ligands shows that the free amino groups are absent.8 (9. 485 cm)1 m(MAN) and 305 cm)1 m(MAS) coupled with other lower vibrational modes of the ligand molecule [11.r.3-diphenyl-1.12-dibenzo [e.3) 4.5) 54. The values of ligand field parameters are consistent with octahedral geometry for the complexes.80 g 1.360.8 701.r.53 53. Related data are listed in Table 3.80 0.0 311. electronic.77–3. at room temperature corresponding to three unpaired electrons. C. where B(free ion) ¼ 918 cm)1. 3. Dqz.0 0.81 0. DT. The first (m1) and second transition (m2) directly give the values of 10Dq and 10Dqxy. Dqy. Dq. spectra of the thiocyanato complexes show a single sharp band at 2089–2083 cm)1 [13] suggesting that both thiocyanato groups are nitrogen-bonded. The g values are calculated from the expression: g ¼ 2:0023ð1 À 4k=10DqÞ where k is the spin orbit coupling constant for the metal ion. are in a similar environment and occupy an axial position.M.091 0. The b values indicate that there is appreciable covalent character in the metal – ligand r bond.7 737.7 267.04 45.87 . The Racah interelectronic repulsion parameter B is calculated from the relation. k and b) have been calculated [17.95 1.6 2537 2507 2783 585. I.165 cm)1. The visible region of the electronic spectra of the L1. The spectra of powdered samples of the complexes show a broad line.552 and 18. Owen [19] noted that the reduction of spin–orbit coupling constant for the free ion value of 90 cm)1 for chromium(III) can be employed as a measure of metal ligand covalency.p.r. 18] for the chromium(III) complexes listed in Table 4.p. Ligand field – parameters Various ligand field parameters (Dt.80 0.0 951.0 571. due to the presence of different donating atoms [15]. Dqxy. The nephlauxetic parameter b is obtained using the relation b ¼ B(complex)/B(free ion). 3.77 3.691 cm)1 ranges corresponding to 4 A2g(F) fi 4T2g(F) and 4A2g(F) fi 4T1g(F) transitions respectively. suggesting an octahedral geometry around the chromium ion [14].r. Ligand field (cm)1) parameters of the CrIII complexes Complex Dq (cm)1) B (cm)1) C (cm)1) b 747 737 605 2988 2948 2420 0.98 1.0 44.99 Table 4.81 3. spectra of the complexes were recorded for polycrystalline samples at room temperature and their values are reported in Table 3. L2 and L3 complexes show m1 at 12.r.114 0. Therefore a six coordinated structure with tetradentate macrocyclic ligands may be suggested for these complexes and related data are listed in Table 2.273 Table 2.81 B.552 and 12. 2 B ¼ 2m 2 1 À 3m1 m2 þ m2 =ð15m2 À 27m1 Þ.M. spectral data of the ligands and their CrIII and MnII complexes Complex [Cr(L1)Cl2] Cl [Cr(L2)Cl2] Cl [Cr(L3)Cl2] Cl [Mn(L1)Cl2] [Mn(L1)(SCN)2] [MnCl2] [Mn(L2)(SCN)2] [Mn(L3)Cl2] [Mn(L3)(SCN)2] m(NH) cm)1 – 3320 – – – 3330 3325 – – m(C@N) cm)1 1627 1627 1607 1608 1607 1604 1609 1600 1595 m(MAN) cm)1 415 469 452 518 517 583 590 510 525 m(MAO) cm)1 404 – – 410 401 – – – – m(MAS) cm)1 – – 309 – – – – 306 310 m(SCN) – – – – 2120 – 2110 – 2115 Bands due to anions The i. The position of the bands indicates that these complexes exhibit octahedral geometry. E. The moments are close to the spin only values.165–15. consistent with D4h symmetry around the metal ion [16].r. spectra The e.p.621–21. 15. B. Ds. spectral and magnetic moment data of the CrIII complexes Complex [Cr(L1)Cl2] Cl [Cr(L2)Cl2] Cl [Cr(L3)Cl2] Cl Dq (cm)1) 1686 1862 2169 B (cm)1) 747 737 605 C (cm)1) 2988 2948 2420 b 0.65 leff B.970 Dt y Dq (cm)1) z Dq (cm)1) Ds (cm)1) 5901 5806 7513 DS 8901 5806 7513 k [Cr(L1)Cl2] Cl 1686 [Cr(L2)Cl2] Cl 1862 [Cr(L3)Cl2] Cl 2169 743. The value of k Table 3. E. The electronic spectra of the complexes recorded in DMF (hplc grade) show two bands in the 12.65 LFSE DT/Dq kJ/mol)1 241.81 0. The transition 4A2g(F) fi 4T1g(P) is usually not observed in the visible region due to involvement of the charge transfer band. Chromium(III) complexes Chromium(III) complexes exhibit magnetic moments. Related data are listed in Table 3. 93 1.98 5.274 indicates that the complexes under study have substantial covalent character. The nuclear magnetic quantum numbers MI corresponding to these lines are )5/2.82 0.91 6. 5.0023).79–0.96 B.r.95 Proposed structure of the CrIII and MnII complexes. )1/2.83) and Hx indicate that the complexes under study have appreciable covalent character.70 F2 1137 1046 1156 968 1229 1060 leff B. Thanks are also due to the Principal. Acknowledgements One of the authors (Kumar) gratefully thanks my younger brother Bitto for motivation. The calculated values of b (0.79 0. In DMF solution the e. The electronic spectra of complexes show bands at 17.150–24. þ1/2. E. 6A1g fi 4Eg (4D) m3 and 6 A1g fi 4T1g (4P) (m4) transitions respectively.r.p.83 0. spectra of the complexes clearly show that. their Table 5. On increasing delocalization the value of b decreases and is less than one in the complexes.p. Zakir Husain College. 6 A1g fi 4Eg (4G) (m2). These bands may be assigned as 6A1g fi 4T1g(4G) (m1). C.57 2.70 2. Slater Condon parameters F2 and F4 are related to the Racah parameters B and C as follows B ¼ F2 À 5F4 . The electron–electron repulsion in the complexes is less than that in the free ion.0 103 65. for providing laboratory facilities.96 1. . resulting in an increased distance between electrons and thus an effective increase in the size of the orbitals.r. since manganese(II) has a d5 electronic configuration.91 5.M. F2 and Hx are calculated and given in Table 5.78 0. F4. in this solvent.000 cm)1 (m4) [22].240 cm)1 (m2).p. Thanks are also due to the SSPL solid state physics lab for recording magnetic moments and the IIT Bombay for recording e. spectra.p.0 Hx 3. b.96 g 1.99 1. Ligand field (cm)1) parameters of the MnII complexes Complex [Mn(L1)Cl2] [Mn(L1)(SCN)2] [Mn(L2)Cl2] [Mn(L2)(SCN)2] [Mn(L3)Cl2] [Mn(L3)(SCN)2] Dq (cm)1) 1785 1765 1750 1745 1710 1735 B (cm)1) 627 481 651 588 614 735 C (cm)1) 3576 3984 3546 2665 3614 2307 b 0. spectra of the complexes have been recorded using polycrystalline samples at room temperature. The polycrystalline samples give one broad isotropic signal centered at ca.94 1.81 F4 102 113 101 76. range at room temperature [21]. and the USIC Delhi University for recording i.00 6.r. )3/2.40 4. Manganese(II) complexes These complexes show magnetic moments in the 5.800 cm)1 (m3) and 31. the free electron g-value (g0 ¼ 2.M. The numerical value 786 cm)1 for the B of the free manganese(II) ion has been used to [25] calculate the value of b. B. Dq can be evaluated with the help of the energy level due [24] to the 6A1g fi 4T1g (4G) transition.100–17. spectra. the UGC New Delhi for financial assistance. It is possible to define the covalency parameter analogous to the nephelauxetic parameter which is the ratio of the spin – orbit coupling constant for the complex and free ion [20]. spectra The e.850 cm)1 (m1) 24.97 1. In the complexes the intensities of electronic transitions from the ground state 6S to states of fourfold multiplicity are very weak. C ¼ 35F4. 28.85 5. 4 A1g ð4 GÞ ¼ 10B þ 5C A1g ! 4 T1g ð4 PÞ ¼ 17B þ 5C 6 The energies of these transitions are independent of the crystal field splitting energy and depend [23] only on the parameters B and C. values Dq.540–28. the complexes existed as monomeric units.00 2.00 2. 6 g values are given in Table 5.81 0. A1g ! 4 Eg.90– 5. þ3/2.r. þ5/2 from low to the high field [26–28]. The ligand field parameter. R. 18. Polyhedron. R. Kostre and A. N. Chem. 1755 (1981). Synth. 15. Inst. Fenton. Verboom. Owen. J. H. Synth. R. K. Johnson. 223. de Blas. 1498 (1984) 26. Rudkevich.M. D. Lindoy. 21. 11. F.H. Inorg. 19.. Chem. Ohba and H.R. Roy. 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