A review of the tripodal Schiff base (SB) complexes of tris(2-aminoethyl)amine, N ap (CH 2 CH 2 N... more A review of the tripodal Schiff base (SB) complexes of tris(2-aminoethyl)amine, N ap (CH 2 CH 2 NH 2) 3 (tren), and a few closely related tripodal amines with Cr(II), Mn(III) (d 4), Mn(II), Fe(III) (d 5), Fe(II) (d 6), and Co(II) (d 7) is provided. Attention is focused on examination of key structural features, the M-N imine , M-N amine , or M-O and M-N ap bond distances and N imine-M-N(O) bite and C-N ap-C angles and how these values correlate with spin state selection and spin crossover (SCO) behavior. A comparison of these experimental values with density functional theory calculated values is also given. The greatest number, 132, of complexes is observed with cationic mononuclear iron(II) in a N 6 donor set, Fe(II)N 6. The dominance of two spin states, high spin (HS) and low spin (LS), in these systems is indicated by the bimodal distribution of histogram plots of Fe(II)-N imine and Fe(II)-N azole/pyridine bond distances and of N imine-Fe(II)-N azole/pyridine and C-N ap-C bond angles. The values of the two maxima, corresponding to LS and HS states, in each of these histograms agree closely with the theoretical values. The iron(II)-N imine and iron(II)-N azole/pyridine bond distances correlate well for these complexes. Examples of SCO complexes of this type are tabulated and a few of the 20 examples are discussed that exhibit interesting features. There are only a few mononuclear iron(III) cationic complexes and one is SCO. In addition, a significant number of supramolecular complexes of these ligands that exhibit SCO, intervalence, and chiral recognition are discussed. A summary is made regarding the current state of this area of research and possible new avenues to explore based on analysis of the present data.
Iron(III) complexes of the diprotic N4 Schiff base macrocycles, 7,8,15,16,17,18-hexahydro-dibenzo... more Iron(III) complexes of the diprotic N4 Schiff base macrocycles, 7,8,15,16,17,18-hexahydro-dibenzo[e,m] [1,4,8,11]tetraazacyclotetradecine (H2(2,2mac)) and 8,9,16,17,18,19-hexahydro-7H-dibenzo[e,n][1,4,8,12]tetraazacyclopentaadecine(H2(3,2mac)), were prepared by the metathesis reaction of anhydrous iron (III) bromide with the disodium or magnesium complexes of the dianionic ligands in THF under an inert atmosphere. The complexes exhibit the intermediate spin state as evidenced by magnetic susceptibility and Mössbauer spectroscopy. Fe(3,2 mac)Br is structurally characterized as a distorted square pyramid with the four nitrogen atoms in the basal positions and the bromide occupying the axial site. The average iron to nitrogen bond distance is 1.921 Å.
ChemInform Abstract The reactions of (I) with the copper complex (II) to yield the imidazolate br... more ChemInform Abstract The reactions of (I) with the copper complex (II) to yield the imidazolate bridged binuclear compounds (III) are followed in the visible spectrum. Equilibrium constants for the reaction are measured in toluene. A correlation between Hammett constants and the nature of substituents at the porphyrin ligand is given. Replacement of Cu in (II) with Ni reduces the equilibrium constants for the reactionwith (I) while the free ligand fails to react at all. Reasons therefore are discussed. The effect of a given solvent (CH2Cl2, toluene, DME, DMSO) on the equilibrium constant for the reaction of (Ia) with N-methylimidazole is investigated.
The aldimine and ketimine forms of two Schiff base complexes formed by the condensation of two is... more The aldimine and ketimine forms of two Schiff base complexes formed by the condensation of two isomeric imidazole carboxaldehydes with an amino acid are reported. Reaction of L 1 , the Schiff base condensate of 5-methyl-4-imidazolecarboxaldehyde (5Me4Im) and valine, with copper(II) perchlorate results in the isolation of [Cu(L 1)(5Me4Im)(ClO 4)] while the analogous reaction of L 2 , the Schiff base condensate of 1-methyl-2imidazolecarboxaldehyde (1Me2Im) with alanine, and nickel(II) results in the isolation of [Ni(L 2) 2 ]. L 1 exhibits the expected aldimine form of the amino acid derived Schiff base, 5Me4Im-CH = N-CH(R)CO 2 − , while L 2 exhibits the tautomeric ketimine form, 1Me2Im-CH 2-N = C(R')CO 2 −. Structural data clearly support the two tautomeric forms. The ketimine form, observed in [Ni(L 2) 2 ], has been proposed as an intermediate in the racemization and transamination of amino acids.
The equilibrium constant and thermodynamic data for the reaction between (I) and 1‐methylimidazol... more The equilibrium constant and thermodynamic data for the reaction between (I) and 1‐methylimidazole in DMSO are determined in the presence and absence of the donor (II) and the acceptor (III).
ChemInform Abstract The Fe(III) tetraphenylporphinate Fe(TPP)Cl is allowed to coordinate axially ... more ChemInform Abstract The Fe(III) tetraphenylporphinate Fe(TPP)Cl is allowed to coordinate axially to the imidazole moiety of the base (I) in DMSO. A bis-adduct is formed yielding the trinuclear system ((I)-Fe(TPP)-(I))+. This fails to be an acceptable model of cytochrome c oxidase (VIS, formation constants).
The 3:1 condensation of 5-methyl-1H-pyrazole-3-carboxaldehyde (MepyrzH) with tris(2-aminoethyl)am... more The 3:1 condensation of 5-methyl-1H-pyrazole-3-carboxaldehyde (MepyrzH) with tris(2-aminoethyl)amine (tren) gives the tripodal ligand tren(MePyrzH) 3. Aerial oxidation of a solution of cobalt(II) with this ligand in the presence of base results in the isolation of the insoluble Co(tren)(MePyrz) 3. This complex reacts with acids, HCl/NaClO 4 , NH 4 ClO 4 , NH 4 BF 4 , and NH 4 I to give the crystalline compounds Co(tren)(MePyrzH) 3 (ClO 4) 3 , {[Co(tren)(MePyrzH 0.5) 3 ](ClO 4) 1.5 } 2 {[Co(tren)(MePyrzH 0.5) 3 ](BF 4) 1.5 } 2 and [Co(tren)(MePyrzH) 3 ][Co(tren)(MePyrzH) 3 ]I 2. The latter three complexes are dimeric, held together by three N pyrazole-H. .. N pyrazolate hydrogen bonds. The structures and symmetries of these homochiral dimers or pseudodimers are discussed in terms of their space group. Possible applications of these complexes by incorporation into new materials are mentioned.
The iron(II) and manganese(II) complexes of the N(7) Schiff-base condensate of tris(3-aminopropyl... more The iron(II) and manganese(II) complexes of the N(7) Schiff-base condensate of tris(3-aminopropyl)amine with 1-methyl-2-imidazolecarbaldehyde and the manganese(II) complex of the N(7) Schiff-base condensate of tris(3-aminopropyl)amine with 4-imidazolecarbaldehyde are high-spin mono capped octahedral seven-coordinate complexes with a short, approximately 2.44 è, metal to apical nitrogen bond.
Three dinuclear complexes formed by the reaction of Gd(hfa) 3 (hfa is hexafluoroacetylacetonate) ... more Three dinuclear complexes formed by the reaction of Gd(hfa) 3 (hfa is hexafluoroacetylacetonate) with Schiff base complexes of Cu(II) and Ni(II) have been synthesized and characterized. The crystal structures of the complexes [Gd(hfa) 3 M(prpen)] {M = Cu(II (1)), Ni(II) (2)} are reported. (H 2 prpen is the Schiff base derived from the condensation of 2 equiv. of 2-hydroxypropiophenone and 1 equiv. of ethylenediamine.) Both 1 and 2 are discrete dinuclear complexes consisting of an eight coordinate Gd atom which is bridged to four coordinate M(II) via both phenolate oxygen atoms of the prpen ligand. The crystal structure shows there is no tendency toward dimerization between adjacent Cu(II) Schiff base units in 1. Cryomagnetic measurements show a ferromagnetic interaction between Gd(III) and Cu(II) in 1 as predicted by theory with J= 1.91 cm − 1. The reaction of Gd(hfa) 3 with Ni(L) (H 2 L is the Schiff base derived from the condensation of 1 equiv. each of 5-chlorobenzophenone, 1,2-diaminobenzene, and 5-methyl-4-imidazolecarboxaldehyde) produced Gd(hfa) 3 Ni(L) (3) in which imidazolate is available to bridge Gd(III) and Ni(II).
ABSTRACT The structures of the copper complexes of 7,8,15,16,17,18-hexahydro-dibenzo[e,m][1,4,8,1... more ABSTRACT The structures of the copper complexes of 7,8,15,16,17,18-hexahydro-dibenzo[e,m][1,4,8,11]tetraazacyclotetradecine (Cu(2,2 mac)) 7,8,15,18-tetrahydro-dibenzo[e,m][1,4,8,11]tetraazacyclotetradecine-16,17-dionato (Cu(2,2 oxomac)) and Cu(NCH3 amben) and Cu(2,2 oxomac)Ni(hfa)2 are reported. The three copper complexes containing a 14-membered macrocycle are essentially square planar complexes and exhibit no short axial interactions. The analogous acyclic complex, Cu(NCH3 amben), exhibits an average tetrahedral distortion of 34.35° which appears to be due to steric repulsion between the two methyl groups. The dinuclear complex, which exhibits a planar exchange coupled oxamido core, was prepared by reaction of Cu(2,2 oxomac) with Ni(hfa)2. The analogous complex, Cu(2,2 oxomac)Cu(hfa)2, can be prepared by the same procedure or by reaction of Cu(2,2 mac) with Cu(hfa)2. The former method is a general synthetic route while the latter is specific for Cu(hfa)2 relying on its ability to catalyze the oxidization of the ethylene unit between the anilino nitrogen atoms to the oxamide (NCH2CH2N to NCOCON) under ambient conditions.
The iron(II) complex of the 1 : 3 Schiff base condensate of tris(2-aminoethyl)amine (tren) with 2... more The iron(II) complex of the 1 : 3 Schiff base condensate of tris(2-aminoethyl)amine (tren) with 2-imidazolecarboxaldehyde, H3L1, [FeH3L1](ClO4)2, was reacted with MClO4 (M = K, Rb, Cs, and NH4). The products were double salts of the formula {[FeH3L1](ClO4)2}·MClO4. The complexes have been characterized by Elemental Analysis, X-ray crystallography, ESMS, IR and Mossbauer spectroscopy. The resultant complexes are all trigonal, crystallize in P and exhibit a hexameric structure in the extended lattice. The cations are located at the origin (0, 0, 0) and c/2 (0, 0, 0.5) on the c axis. The cations are twelve coordinate and exhibit a distorted icosahedral geometry formed by six bidentate perchlorate anions. The perchlorate anions are involved in extensive hydrogen bonding with the iron complexes, which are located at the vertices of the hexagon. Each perchlorate anion has five hydrogen bonds to three iron complexes. The iron complexes use the imidazole NH and imine NCH as donors to the perchlorate oxygen atoms. The imidazole NH is a trifurcated donor and the imine CH is a bifurcated donor. The formation of the double salt and the accompanying hydrogen bonding results in a shift in the spin equilibrium of the parent iron(II) complex from 63% high spin, HS, and 37% low spin, LS, at 295 K to pure LS in the double salts. Attempts to incorporate sodium or silver in the above salts failed due to their size and oxidizing strength, respectively. The analogous manganese complex, [MnH3L1](ClO4)2, failed to give these double salts under identical reaction conditions. The lack of reactivity of [MnH3L1](ClO4)2 does not appear to be due to its solubility or geometric considerations of the hydrogen bonding donor site, but instead to the electronic differences between the high spin [MnH3L1](ClO4)2 and the spin crossover [FeH3L1](ClO4)2.
characterization of manganese(II) and iron(III) d 5 tripodal imidazole complexes. Effect of oxida... more characterization of manganese(II) and iron(III) d 5 tripodal imidazole complexes. Effect of oxidation state, protonation state and ligand conformation on coordination number and spin state Cynthia Brewer a , Greg Brewer* a , Ray J. Butcher b , Everett E. Carpenter c , Luciann Cuenca a ,
ChemInform Abstract The complex system (I), containing a Fe(II) porphyrin, is isolated by reactio... more ChemInform Abstract The complex system (I), containing a Fe(II) porphyrin, is isolated by reaction of the components in toluene. The Ni-Fe-Ni system is an all-diamagnetic trinuclear species and the Cu-Fe-Cu system consists of magnetically isolated Cu(II) centers separated by diamagnetic iron(II). The chemistry of the Fe(III) porphyrin is investigated with the large weakly coordinating anion CB11H12. Treatment of the porphyrinatoiron(III) complex with the Ni or Cu salt of the Schiff base in THF produces essentially quantitative yields of the corresponding salts of (I). The Cu complex, crystallizing in P1 with Z=2, represents the first example of intramolecular ferromagnetic coupling via imidazolate bridging ligands in a heterotrinuclear system. The magnetic properties of the Ni species are entirely typical of a low-spin S = 1/2 bis-imidazole iron(III) porphyrin.
Abstract The synthesis of cobalt and chromium complexes of H 4 ATP and H 4 GTP in which the metal... more Abstract The synthesis of cobalt and chromium complexes of H 4 ATP and H 4 GTP in which the metal is asymmetric are reported. These compounds were characterized by visible spectroscopy, fast atom bombardment mass spectroscopy (FAB MS), and 31 P NMR. The mass spectral data allow identification of the complexes to be made from ions in the molecular weight region. The effect of an asymmetric metal greatly alters the appearance of the 31 P NMR spectra in comparison to complexes which do not have this feature. Complexes of uridine diphosphoglucose, UDPG, are also reported. The effect of an asymmetric metal ion on the chromatographic and spectral properties of the complexes are discussed.
A review of the tripodal Schiff base (SB) complexes of tris(2-aminoethyl)amine, N ap (CH 2 CH 2 N... more A review of the tripodal Schiff base (SB) complexes of tris(2-aminoethyl)amine, N ap (CH 2 CH 2 NH 2) 3 (tren), and a few closely related tripodal amines with Cr(II), Mn(III) (d 4), Mn(II), Fe(III) (d 5), Fe(II) (d 6), and Co(II) (d 7) is provided. Attention is focused on examination of key structural features, the M-N imine , M-N amine , or M-O and M-N ap bond distances and N imine-M-N(O) bite and C-N ap-C angles and how these values correlate with spin state selection and spin crossover (SCO) behavior. A comparison of these experimental values with density functional theory calculated values is also given. The greatest number, 132, of complexes is observed with cationic mononuclear iron(II) in a N 6 donor set, Fe(II)N 6. The dominance of two spin states, high spin (HS) and low spin (LS), in these systems is indicated by the bimodal distribution of histogram plots of Fe(II)-N imine and Fe(II)-N azole/pyridine bond distances and of N imine-Fe(II)-N azole/pyridine and C-N ap-C bond angles. The values of the two maxima, corresponding to LS and HS states, in each of these histograms agree closely with the theoretical values. The iron(II)-N imine and iron(II)-N azole/pyridine bond distances correlate well for these complexes. Examples of SCO complexes of this type are tabulated and a few of the 20 examples are discussed that exhibit interesting features. There are only a few mononuclear iron(III) cationic complexes and one is SCO. In addition, a significant number of supramolecular complexes of these ligands that exhibit SCO, intervalence, and chiral recognition are discussed. A summary is made regarding the current state of this area of research and possible new avenues to explore based on analysis of the present data.
Iron(III) complexes of the diprotic N4 Schiff base macrocycles, 7,8,15,16,17,18-hexahydro-dibenzo... more Iron(III) complexes of the diprotic N4 Schiff base macrocycles, 7,8,15,16,17,18-hexahydro-dibenzo[e,m] [1,4,8,11]tetraazacyclotetradecine (H2(2,2mac)) and 8,9,16,17,18,19-hexahydro-7H-dibenzo[e,n][1,4,8,12]tetraazacyclopentaadecine(H2(3,2mac)), were prepared by the metathesis reaction of anhydrous iron (III) bromide with the disodium or magnesium complexes of the dianionic ligands in THF under an inert atmosphere. The complexes exhibit the intermediate spin state as evidenced by magnetic susceptibility and Mössbauer spectroscopy. Fe(3,2 mac)Br is structurally characterized as a distorted square pyramid with the four nitrogen atoms in the basal positions and the bromide occupying the axial site. The average iron to nitrogen bond distance is 1.921 Å.
ChemInform Abstract The reactions of (I) with the copper complex (II) to yield the imidazolate br... more ChemInform Abstract The reactions of (I) with the copper complex (II) to yield the imidazolate bridged binuclear compounds (III) are followed in the visible spectrum. Equilibrium constants for the reaction are measured in toluene. A correlation between Hammett constants and the nature of substituents at the porphyrin ligand is given. Replacement of Cu in (II) with Ni reduces the equilibrium constants for the reactionwith (I) while the free ligand fails to react at all. Reasons therefore are discussed. The effect of a given solvent (CH2Cl2, toluene, DME, DMSO) on the equilibrium constant for the reaction of (Ia) with N-methylimidazole is investigated.
The aldimine and ketimine forms of two Schiff base complexes formed by the condensation of two is... more The aldimine and ketimine forms of two Schiff base complexes formed by the condensation of two isomeric imidazole carboxaldehydes with an amino acid are reported. Reaction of L 1 , the Schiff base condensate of 5-methyl-4-imidazolecarboxaldehyde (5Me4Im) and valine, with copper(II) perchlorate results in the isolation of [Cu(L 1)(5Me4Im)(ClO 4)] while the analogous reaction of L 2 , the Schiff base condensate of 1-methyl-2imidazolecarboxaldehyde (1Me2Im) with alanine, and nickel(II) results in the isolation of [Ni(L 2) 2 ]. L 1 exhibits the expected aldimine form of the amino acid derived Schiff base, 5Me4Im-CH = N-CH(R)CO 2 − , while L 2 exhibits the tautomeric ketimine form, 1Me2Im-CH 2-N = C(R')CO 2 −. Structural data clearly support the two tautomeric forms. The ketimine form, observed in [Ni(L 2) 2 ], has been proposed as an intermediate in the racemization and transamination of amino acids.
The equilibrium constant and thermodynamic data for the reaction between (I) and 1‐methylimidazol... more The equilibrium constant and thermodynamic data for the reaction between (I) and 1‐methylimidazole in DMSO are determined in the presence and absence of the donor (II) and the acceptor (III).
ChemInform Abstract The Fe(III) tetraphenylporphinate Fe(TPP)Cl is allowed to coordinate axially ... more ChemInform Abstract The Fe(III) tetraphenylporphinate Fe(TPP)Cl is allowed to coordinate axially to the imidazole moiety of the base (I) in DMSO. A bis-adduct is formed yielding the trinuclear system ((I)-Fe(TPP)-(I))+. This fails to be an acceptable model of cytochrome c oxidase (VIS, formation constants).
The 3:1 condensation of 5-methyl-1H-pyrazole-3-carboxaldehyde (MepyrzH) with tris(2-aminoethyl)am... more The 3:1 condensation of 5-methyl-1H-pyrazole-3-carboxaldehyde (MepyrzH) with tris(2-aminoethyl)amine (tren) gives the tripodal ligand tren(MePyrzH) 3. Aerial oxidation of a solution of cobalt(II) with this ligand in the presence of base results in the isolation of the insoluble Co(tren)(MePyrz) 3. This complex reacts with acids, HCl/NaClO 4 , NH 4 ClO 4 , NH 4 BF 4 , and NH 4 I to give the crystalline compounds Co(tren)(MePyrzH) 3 (ClO 4) 3 , {[Co(tren)(MePyrzH 0.5) 3 ](ClO 4) 1.5 } 2 {[Co(tren)(MePyrzH 0.5) 3 ](BF 4) 1.5 } 2 and [Co(tren)(MePyrzH) 3 ][Co(tren)(MePyrzH) 3 ]I 2. The latter three complexes are dimeric, held together by three N pyrazole-H. .. N pyrazolate hydrogen bonds. The structures and symmetries of these homochiral dimers or pseudodimers are discussed in terms of their space group. Possible applications of these complexes by incorporation into new materials are mentioned.
The iron(II) and manganese(II) complexes of the N(7) Schiff-base condensate of tris(3-aminopropyl... more The iron(II) and manganese(II) complexes of the N(7) Schiff-base condensate of tris(3-aminopropyl)amine with 1-methyl-2-imidazolecarbaldehyde and the manganese(II) complex of the N(7) Schiff-base condensate of tris(3-aminopropyl)amine with 4-imidazolecarbaldehyde are high-spin mono capped octahedral seven-coordinate complexes with a short, approximately 2.44 è, metal to apical nitrogen bond.
Three dinuclear complexes formed by the reaction of Gd(hfa) 3 (hfa is hexafluoroacetylacetonate) ... more Three dinuclear complexes formed by the reaction of Gd(hfa) 3 (hfa is hexafluoroacetylacetonate) with Schiff base complexes of Cu(II) and Ni(II) have been synthesized and characterized. The crystal structures of the complexes [Gd(hfa) 3 M(prpen)] {M = Cu(II (1)), Ni(II) (2)} are reported. (H 2 prpen is the Schiff base derived from the condensation of 2 equiv. of 2-hydroxypropiophenone and 1 equiv. of ethylenediamine.) Both 1 and 2 are discrete dinuclear complexes consisting of an eight coordinate Gd atom which is bridged to four coordinate M(II) via both phenolate oxygen atoms of the prpen ligand. The crystal structure shows there is no tendency toward dimerization between adjacent Cu(II) Schiff base units in 1. Cryomagnetic measurements show a ferromagnetic interaction between Gd(III) and Cu(II) in 1 as predicted by theory with J= 1.91 cm − 1. The reaction of Gd(hfa) 3 with Ni(L) (H 2 L is the Schiff base derived from the condensation of 1 equiv. each of 5-chlorobenzophenone, 1,2-diaminobenzene, and 5-methyl-4-imidazolecarboxaldehyde) produced Gd(hfa) 3 Ni(L) (3) in which imidazolate is available to bridge Gd(III) and Ni(II).
ABSTRACT The structures of the copper complexes of 7,8,15,16,17,18-hexahydro-dibenzo[e,m][1,4,8,1... more ABSTRACT The structures of the copper complexes of 7,8,15,16,17,18-hexahydro-dibenzo[e,m][1,4,8,11]tetraazacyclotetradecine (Cu(2,2 mac)) 7,8,15,18-tetrahydro-dibenzo[e,m][1,4,8,11]tetraazacyclotetradecine-16,17-dionato (Cu(2,2 oxomac)) and Cu(NCH3 amben) and Cu(2,2 oxomac)Ni(hfa)2 are reported. The three copper complexes containing a 14-membered macrocycle are essentially square planar complexes and exhibit no short axial interactions. The analogous acyclic complex, Cu(NCH3 amben), exhibits an average tetrahedral distortion of 34.35° which appears to be due to steric repulsion between the two methyl groups. The dinuclear complex, which exhibits a planar exchange coupled oxamido core, was prepared by reaction of Cu(2,2 oxomac) with Ni(hfa)2. The analogous complex, Cu(2,2 oxomac)Cu(hfa)2, can be prepared by the same procedure or by reaction of Cu(2,2 mac) with Cu(hfa)2. The former method is a general synthetic route while the latter is specific for Cu(hfa)2 relying on its ability to catalyze the oxidization of the ethylene unit between the anilino nitrogen atoms to the oxamide (NCH2CH2N to NCOCON) under ambient conditions.
The iron(II) complex of the 1 : 3 Schiff base condensate of tris(2-aminoethyl)amine (tren) with 2... more The iron(II) complex of the 1 : 3 Schiff base condensate of tris(2-aminoethyl)amine (tren) with 2-imidazolecarboxaldehyde, H3L1, [FeH3L1](ClO4)2, was reacted with MClO4 (M = K, Rb, Cs, and NH4). The products were double salts of the formula {[FeH3L1](ClO4)2}·MClO4. The complexes have been characterized by Elemental Analysis, X-ray crystallography, ESMS, IR and Mossbauer spectroscopy. The resultant complexes are all trigonal, crystallize in P and exhibit a hexameric structure in the extended lattice. The cations are located at the origin (0, 0, 0) and c/2 (0, 0, 0.5) on the c axis. The cations are twelve coordinate and exhibit a distorted icosahedral geometry formed by six bidentate perchlorate anions. The perchlorate anions are involved in extensive hydrogen bonding with the iron complexes, which are located at the vertices of the hexagon. Each perchlorate anion has five hydrogen bonds to three iron complexes. The iron complexes use the imidazole NH and imine NCH as donors to the perchlorate oxygen atoms. The imidazole NH is a trifurcated donor and the imine CH is a bifurcated donor. The formation of the double salt and the accompanying hydrogen bonding results in a shift in the spin equilibrium of the parent iron(II) complex from 63% high spin, HS, and 37% low spin, LS, at 295 K to pure LS in the double salts. Attempts to incorporate sodium or silver in the above salts failed due to their size and oxidizing strength, respectively. The analogous manganese complex, [MnH3L1](ClO4)2, failed to give these double salts under identical reaction conditions. The lack of reactivity of [MnH3L1](ClO4)2 does not appear to be due to its solubility or geometric considerations of the hydrogen bonding donor site, but instead to the electronic differences between the high spin [MnH3L1](ClO4)2 and the spin crossover [FeH3L1](ClO4)2.
characterization of manganese(II) and iron(III) d 5 tripodal imidazole complexes. Effect of oxida... more characterization of manganese(II) and iron(III) d 5 tripodal imidazole complexes. Effect of oxidation state, protonation state and ligand conformation on coordination number and spin state Cynthia Brewer a , Greg Brewer* a , Ray J. Butcher b , Everett E. Carpenter c , Luciann Cuenca a ,
ChemInform Abstract The complex system (I), containing a Fe(II) porphyrin, is isolated by reactio... more ChemInform Abstract The complex system (I), containing a Fe(II) porphyrin, is isolated by reaction of the components in toluene. The Ni-Fe-Ni system is an all-diamagnetic trinuclear species and the Cu-Fe-Cu system consists of magnetically isolated Cu(II) centers separated by diamagnetic iron(II). The chemistry of the Fe(III) porphyrin is investigated with the large weakly coordinating anion CB11H12. Treatment of the porphyrinatoiron(III) complex with the Ni or Cu salt of the Schiff base in THF produces essentially quantitative yields of the corresponding salts of (I). The Cu complex, crystallizing in P1 with Z=2, represents the first example of intramolecular ferromagnetic coupling via imidazolate bridging ligands in a heterotrinuclear system. The magnetic properties of the Ni species are entirely typical of a low-spin S = 1/2 bis-imidazole iron(III) porphyrin.
Abstract The synthesis of cobalt and chromium complexes of H 4 ATP and H 4 GTP in which the metal... more Abstract The synthesis of cobalt and chromium complexes of H 4 ATP and H 4 GTP in which the metal is asymmetric are reported. These compounds were characterized by visible spectroscopy, fast atom bombardment mass spectroscopy (FAB MS), and 31 P NMR. The mass spectral data allow identification of the complexes to be made from ions in the molecular weight region. The effect of an asymmetric metal greatly alters the appearance of the 31 P NMR spectra in comparison to complexes which do not have this feature. Complexes of uridine diphosphoglucose, UDPG, are also reported. The effect of an asymmetric metal ion on the chromatographic and spectral properties of the complexes are discussed.
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Papers by Greg A Brewer