Synthesis, Reactivities, and Magnetostructural Properties of FeIII, FeIII-O-FeIII, and ZnIIFeIII-O-FeIIIZnII Complexes of a
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- 作者：Papu Biswas ; Meenakshi Ghosh ; Sujit K. Dutta ; Ulrich Flö ; rke ; and Kamalaksha Nag
- 刊名：Inorganic Chemistry
- 出版年：2006
- 出版时间：June 12, 2006
- 年：2006
- 卷：45
- 期：12
- 页码：4830 - 4844
- 全文大小：321K
- 年卷期：v.45,no.12(June 12, 2006)
- ISSN：1520-510X
文摘
The mononuclear iron(III) complexes [Fe(LH2)(H2O)Cl](ClO4)2·2H2O (1) and [Fe(LH2)(H2O)2](ClO4)3·H2O (2) havebeen prepared by reacting [Pb(LH2)](ClO4)2 with FeCl3·6H2O and Fe(ClO4)3·6H2O, respectively. Complex 2 upontreatment with 1 equiv of alkali produces the oxo-bridged dimer [{Fe(LH2)(H2O)}2(
-O)](ClO4)4·2H2O (3). In thesecompounds, LH2 refers to the tetraiminodiphenol macrocycle in the zwitterionic form whose two uncoordinatedimine nitrogens are protonated and hydrogen-bonded to the metal-bound phenolate oxygens. The aqua ligands ofcomplexes 1-3 get exchanged in acetonitrile. Reaction equilibria involving binding and exchange of the terminalligands (Cl-/H2O/CH3CN) in these complexes have been studied spectrophotometrically. The equilibrium constantfor the aquation reaction (Kaq) [1]2+ + H2O 
[2]3+ + Cl- in acetonitrile is 8.65(5) M, and the binding constant(KCl-) for the reaction [1]2+ + Cl- 
[1Cl]+ + CH3CN is 4.75(5) M. The pKD value for the dimerization reaction2[2]3+ + 2OH- 
[3]4+ + 3H2O in 1:1 acetonitrile-water is 9.38(10). Complexes 1-3 upon reaction with Zn(ClO4)2·6H2O and sodium acetate (OAc), pivalate (OPiv), or bis(4-nitrophenyl)phosphate (BNPP) produce theheterobimetallic complexes [{FeLZn(-X)}2(-O)](ClO4)2, where X = OAc (4), OPiv (5), and BNPP (6). The pseudo-first-order rate constant (kobs) for the formation of 4 at 25 
C from either 1 or 3 with an excess of Zn(OAc)2·2H2Oin 1:1 acetonitrile-water at pH 6.6 is found to be the same with kobs = 1.6(2) × 10-4 s-1. The X-ray crystalstructures of 3, 4, and 6 have been determined, although the structure determination of 3 was severely affectedbecause of heavy disordering. In 3, the Fe-O-Fe angle is 168.6(6), while it is exactly 180.0 in 4 and 6. Cyclicand square-wave voltammetric (CV and SWV) measurements have been carried out for complexes 1-4 in acetonitrile.The variation of the solvent composition (acetonitrile-water) has a profound effect on the E1/2 and 
Ep values. Thebinding of an additional chloride ion to an iron(III) center in 1-3 is accompanied by a remarkable shift of E1/2 tomore negative values. The observation of quasi-reversible CV for complexes containing a FeIII -O-FeIII unit (3 and4) indicates that in the electrochemical time scale unusual FeIII-O-FeII is produced. The 1H NMR spectra of complexes3-6 exhibit hyperfine-shifted signals in the range 0-90 ppm with similar features. The metal-hydrogen distancesobtained from T1 measurements are in good agreement with the crystallographic data. Variable-temperature (2-300 K) magnetic susceptibility measurements carried out for 3 and 4 indicate strong antiferromagnetic exchangeinteraction (H = -2JS1·S2) between the high-spin iron(III) centers in the Fe-O-Fe unit with J = -114 cm-1 (3)and -107 cm-1 (4).
-O)](ClO4)4·2H2O (3). In thesecompounds, LH2 refers to the tetraiminodiphenol macrocycle in the zwitterionic form whose two uncoordinatedimine nitrogens are protonated and hydrogen-bonded to the metal-bound phenolate oxygens. The aqua ligands ofcomplexes 1-3 get exchanged in acetonitrile. Reaction equilibria involving binding and exchange of the terminalligands (Cl-/H2O/CH3CN) in these complexes have been studied spectrophotometrically. The equilibrium constantfor the aquation reaction (Kaq) [1]2+ + H2O [2]3+ + Cl- in acetonitrile is 8.65(5) M, and the binding constant(KCl-) for the reaction [1]2+ + Cl- [1Cl]+ + CH3CN is 4.75(5) M. The pKD value for the dimerization reaction2[2]3+ + 2OH- [3]4+ + 3H2O in 1:1 acetonitrile-water is 9.38(10). Complexes 1-3 upon reaction with Zn(ClO4)2·6H2O and sodium acetate (OAc), pivalate (OPiv), or bis(4-nitrophenyl)phosphate (BNPP) produce theheterobimetallic complexes [{FeLZn(-X)}2(-O)](ClO4)2, where X = OAc (4), OPiv (5), and BNPP (6). The pseudo-first-order rate constant (kobs) for the formation of 4 at 25 C from either 1 or 3 with an excess of Zn(OAc)2·2H2Oin 1:1 acetonitrile-water at pH 6.6 is found to be the same with kobs = 1.6(2) × 10-4 s-1. The X-ray crystalstructures of 3, 4, and 6 have been determined, although the structure determination of 3 was severely affectedbecause of heavy disordering. In 3, the Fe-O-Fe angle is 168.6(6), while it is exactly 180.0 in 4 and 6. Cyclicand square-wave voltammetric (CV and SWV) measurements have been carried out for complexes 1-4 in acetonitrile.The variation of the solvent composition (acetonitrile-water) has a profound effect on the E1/2 and Ep values. Thebinding of an additional chloride ion to an iron(III) center in 1-3 is accompanied by a remarkable shift of E1/2 tomore negative values. The observation of quasi-reversible CV for complexes containing a FeIII -O-FeIII unit (3 and4) indicates that in the electrochemical time scale unusual FeIII-O-FeII is produced. The 1H NMR spectra of complexes3-6 exhibit hyperfine-shifted signals in the range 0-90 ppm with similar features. The metal-hydrogen distancesobtained from T1 measurements are in good agreement with the crystallographic data. Variable-temperature (2-300 K) magnetic susceptibility measurements carried out for 3 and 4 indicate strong antiferromagnetic exchangeinteraction (H = -2JS1·S2) between the high-spin iron(III) centers in the Fe-O-Fe unit with J = -114 cm-1 (3)and -107 cm-1 (4).