A Fourth Isolated Oxidation Level of the [Mn₁₂O₁₂(O₂CR)₁₆(H₂O)₄] Family of Single-Molecule Magnets

The Mn12 family of single-molecule magnets (SMMs) has been extended to a fourth isolated member. [Mn12O12(O2CR)16(H2O)4] (1) exhibits three quasi-reversible one-electron-reduction processes at significantly higher potentials than [Mn12O12(O2CMe)16(H2O)4]. This has allowed the previous generation and isolation of the one- and two-electron-reduced versions of 1 to now be extended to the three-electron-reduced complex. For cation consistency and better comparisons, the complete series of complexes has been prepared with NPrn4+ counterions. Thus, complex 1 was treated with 1, 2, and 3 equiv of NPrn4I, and this led to the successful isolation of (NPrn4)[Mn12O12(O2CCHCl2)16(H2O)4] (2), (NPrn4)2[Mn12O12(O2CCHCl2)16(H2O)4] (3), and (NPrn4)3[Mn12O12(O2CCHCl2)16(H2O)4] (4), respectively. Another three-electron-reduced analogue (NMe4)3[Mn12O12(O2CCHCl2)16(H2O)4] (5) was prepared by the addition of 3 equiv of NMe4I to 1. Direct current magnetization data were collected on dried microcrystalline samples of 2−5 and were fit by matrix diagonalization methods to give S = 19/2, D = −0.35 cm-1, and g = 1.95 for 2; S = 10, D = −0.28 cm-1, and g = 1.98 for 3; S = 17/2, D = −0.25 cm-1, and g = 1.91 for 4; and S = 17/2, D = −0.23 cm-1, and g = 1.90 for 5, where D is the axial zero-field splitting parameter. Thus, the [Mn12]3- complexes 4 and 5 possess significantly decreased absolute magnitudes of both S and D as a result of the three-electron addition to 1, which has S = 10 and D = −0.45 cm-1. The D value of the series 1−4/5 shows a monotonic decrease with electron addition that is consistent with the progressive loss of MnIII ions, which are the primary source of the molecular anisotropy. Nevertheless, when studied by ac susceptibility techniques, the [Mn12]3- complexes still exhibit frequency-dependent out-of-phase susceptibility signals at ≤2.5 K, indicating them to be single-molecule magnets (SMMs), albeit at lower temperatures compared with 1 (6−8 K range), 2 (4−6 K range), and 3 (2−4 K range); the shifts to lower temperatures reflect the decreasing S and D values upon successive reduction and hence the decreasing energy barrier to magnetization relaxation. Thus, the [Mn12]3- complexes represent a fourth isolated oxidation level of the Mn12 family of SMMs, by far the largest range of oxidation levels yet encountered within single-molecule magnetism

A New N,N,O Chelate for Transition Metal Chemistry: Fe₅ and Fe₆ Clusters from the Use of 6-Hydroxymethyl-2,2‘-bipyridine (hmbpH)

The initial use of the anion of 6-hydroxymethyl-2,2‘-bipyridine (hmbpH) as a chelate in coordination chemistry is described. The syntheses, crystal structures, and magnetochemical characterization are reported of four new iron(III) clusters [Fe5O2(OH)(O2CMe)5(hmbp)3](ClO4)2 (1) and [Fe6O2(OH)2(O2CR)6(hmbp)4](NO3)2 (R = Ph (2), Me (3), But (4); hmbpH = 6-hydroxymethyl-2,2‘-bipyridine). The reaction of Fe(ClO4)3, hmbpH, and sodium acetate in a 1:1:∼4 ratio in EtOH gave 1, and the reaction between [Fe3O(O2CR)6(H2O)3](NO3) (R = Ph, Me, But) and hmbpH in a 1:1 ratio in MeCN gave 2−4, respectively. The core of 1 consists of a [Fe4(μ3-O)2]8+ butterfly unit to which is attached a fifth Fe atom by bridging O atoms. The core of 2−4 also consists of a [Fe4(μ3-O)2]8+ butterfly unit to which are attached an Fe atom on either side by bridging O atoms. Variable-temperature (T) and -field (H) solid-state DC and AC magnetization (M) studies were carried out on complexes 1−4 in the 5.0−300 K range. Fitting of the data revealed that 1 has an S = 5/2 ground state spin whereas 2−4 possess an S = 5 ground state. Fitting of the M/NμB vs H/T data by matrix diagonalization and including only axial zero-field splitting (ZFS) gave values of the axial ZFS parameter |D| of 0.75, 0.36, 0.46, and 0.36 cm-1 for 1−4, respectively

Unusual Structural Types in Manganese Cluster Chemistry from the Use of <i>N</i>,<i>N</i>,<i>N</i>‘,<i>N</i>‘-Tetrakis(2-hydroxyethyl)ethylenediamine: Mn₈, Mn₁₂, and Mn₂₀ Clusters

The syntheses, crystal structures, and magnetochemical characterization are reported for three new mixed-valent Mn clusters [Mn8O3(OH)(OMe)(O2CPh)7(edte)(edteH2)](O2CPh) (1), [Mn12O4(OH)2(edte)4Cl6(H2O)2] (2), and [Mn20O8(OH)4(O2CMe)6(edte)6](ClO4)2 (3) (edteH4 = (HOCH2CH2)2NCH2CH2N(CH2CH2OH)2 = N,N,N‘,N‘-tetrakis(2-hydroxyethyl)ethylenediamine). The reaction of edteH4 with Mn(O2CPh)2, MnCl2, or Mn(O2CMe)2 gives 1, 2, and 3, respectively, which all possess unprecedented core topologies. The core of 1 comprises two edge-sharing [Mn4O4] cubanes connected to an additional Mn ion by a μ3-OH- ion and two alkoxide arms of edteH22-. The core of 2 consists of a [Mn12(μ4-O)4]24+ unit with S4 symmetry. The core of 3 consists of six fused [Mn4O4] cubanes in a 3 × 2 arrangement and linked to three additional Mn atoms at both ends. Variable-temperature, solid-state dc and ac magnetization (M) studies were carried out on complexes 1−3 in the 5.0−300 K range. Fitting of the obtained M/NμB vs H/T data by matrix diagonalization and including only axial zero-field splitting (ZFS) gave ground-state spin (S) and axial ZFS parameter (D) of S = 8, D = −0.30 cm-1 for 1, S = 7, D = −0.16 cm-1 for 2, and S = 8, D = −0.16 cm-1 for 3. The combined work demonstrates that four hydroxyethyl arms on an ethylenediamine backbone can generate novel Mn structural types not accessible with other alcohol-based ligands

A New N,N,O Chelate for Transition Metal Chemistry: Fe₅ and Fe₆ Clusters from the Use of 6-Hydroxymethyl-2,2‘-bipyridine (hmbpH)

The initial use of the anion of 6-hydroxymethyl-2,2‘-bipyridine (hmbpH) as a chelate in coordination chemistry is described. The syntheses, crystal structures, and magnetochemical characterization are reported of four new iron(III) clusters [Fe5O2(OH)(O2CMe)5(hmbp)3](ClO4)2 (1) and [Fe6O2(OH)2(O2CR)6(hmbp)4](NO3)2 (R = Ph (2), Me (3), But (4); hmbpH = 6-hydroxymethyl-2,2‘-bipyridine). The reaction of Fe(ClO4)3, hmbpH, and sodium acetate in a 1:1:∼4 ratio in EtOH gave 1, and the reaction between [Fe3O(O2CR)6(H2O)3](NO3) (R = Ph, Me, But) and hmbpH in a 1:1 ratio in MeCN gave 2−4, respectively. The core of 1 consists of a [Fe4(μ3-O)2]8+ butterfly unit to which is attached a fifth Fe atom by bridging O atoms. The core of 2−4 also consists of a [Fe4(μ3-O)2]8+ butterfly unit to which are attached an Fe atom on either side by bridging O atoms. Variable-temperature (T) and -field (H) solid-state DC and AC magnetization (M) studies were carried out on complexes 1−4 in the 5.0−300 K range. Fitting of the data revealed that 1 has an S = 5/2 ground state spin whereas 2−4 possess an S = 5 ground state. Fitting of the M/NμB vs H/T data by matrix diagonalization and including only axial zero-field splitting (ZFS) gave values of the axial ZFS parameter |D| of 0.75, 0.36, 0.46, and 0.36 cm-1 for 1−4, respectively

A New N,N,O Chelate for Transition Metal Chemistry: Fe₅ and Fe₆ Clusters from the Use of 6-Hydroxymethyl-2,2‘-bipyridine (hmbpH)

The initial use of the anion of 6-hydroxymethyl-2,2‘-bipyridine (hmbpH) as a chelate in coordination chemistry is described. The syntheses, crystal structures, and magnetochemical characterization are reported of four new iron(III) clusters [Fe5O2(OH)(O2CMe)5(hmbp)3](ClO4)2 (1) and [Fe6O2(OH)2(O2CR)6(hmbp)4](NO3)2 (R = Ph (2), Me (3), But (4); hmbpH = 6-hydroxymethyl-2,2‘-bipyridine). The reaction of Fe(ClO4)3, hmbpH, and sodium acetate in a 1:1:∼4 ratio in EtOH gave 1, and the reaction between [Fe3O(O2CR)6(H2O)3](NO3) (R = Ph, Me, But) and hmbpH in a 1:1 ratio in MeCN gave 2−4, respectively. The core of 1 consists of a [Fe4(μ3-O)2]8+ butterfly unit to which is attached a fifth Fe atom by bridging O atoms. The core of 2−4 also consists of a [Fe4(μ3-O)2]8+ butterfly unit to which are attached an Fe atom on either side by bridging O atoms. Variable-temperature (T) and -field (H) solid-state DC and AC magnetization (M) studies were carried out on complexes 1−4 in the 5.0−300 K range. Fitting of the data revealed that 1 has an S = 5/2 ground state spin whereas 2−4 possess an S = 5 ground state. Fitting of the M/NμB vs H/T data by matrix diagonalization and including only axial zero-field splitting (ZFS) gave values of the axial ZFS parameter |D| of 0.75, 0.36, 0.46, and 0.36 cm-1 for 1−4, respectively

A New N,N,O Chelate for Transition Metal Chemistry: Fe₅ and Fe₆ Clusters from the Use of 6-Hydroxymethyl-2,2‘-bipyridine (hmbpH)

The initial use of the anion of 6-hydroxymethyl-2,2‘-bipyridine (hmbpH) as a chelate in coordination chemistry is described. The syntheses, crystal structures, and magnetochemical characterization are reported of four new iron(III) clusters [Fe5O2(OH)(O2CMe)5(hmbp)3](ClO4)2 (1) and [Fe6O2(OH)2(O2CR)6(hmbp)4](NO3)2 (R = Ph (2), Me (3), But (4); hmbpH = 6-hydroxymethyl-2,2‘-bipyridine). The reaction of Fe(ClO4)3, hmbpH, and sodium acetate in a 1:1:∼4 ratio in EtOH gave 1, and the reaction between [Fe3O(O2CR)6(H2O)3](NO3) (R = Ph, Me, But) and hmbpH in a 1:1 ratio in MeCN gave 2−4, respectively. The core of 1 consists of a [Fe4(μ3-O)2]8+ butterfly unit to which is attached a fifth Fe atom by bridging O atoms. The core of 2−4 also consists of a [Fe4(μ3-O)2]8+ butterfly unit to which are attached an Fe atom on either side by bridging O atoms. Variable-temperature (T) and -field (H) solid-state DC and AC magnetization (M) studies were carried out on complexes 1−4 in the 5.0−300 K range. Fitting of the data revealed that 1 has an S = 5/2 ground state spin whereas 2−4 possess an S = 5 ground state. Fitting of the M/NμB vs H/T data by matrix diagonalization and including only axial zero-field splitting (ZFS) gave values of the axial ZFS parameter |D| of 0.75, 0.36, 0.46, and 0.36 cm-1 for 1−4, respectively

Unusual Structural Types in Manganese Cluster Chemistry from the Use of <i>N</i>,<i>N</i>,<i>N</i>‘,<i>N</i>‘-Tetrakis(2-hydroxyethyl)ethylenediamine: Mn₈, Mn₁₂, and Mn₂₀ Clusters

The syntheses, crystal structures, and magnetochemical characterization are reported for three new mixed-valent Mn clusters [Mn8O3(OH)(OMe)(O2CPh)7(edte)(edteH2)](O2CPh) (1), [Mn12O4(OH)2(edte)4Cl6(H2O)2] (2), and [Mn20O8(OH)4(O2CMe)6(edte)6](ClO4)2 (3) (edteH4 = (HOCH2CH2)2NCH2CH2N(CH2CH2OH)2 = N,N,N‘,N‘-tetrakis(2-hydroxyethyl)ethylenediamine). The reaction of edteH4 with Mn(O2CPh)2, MnCl2, or Mn(O2CMe)2 gives 1, 2, and 3, respectively, which all possess unprecedented core topologies. The core of 1 comprises two edge-sharing [Mn4O4] cubanes connected to an additional Mn ion by a μ3-OH- ion and two alkoxide arms of edteH22-. The core of 2 consists of a [Mn12(μ4-O)4]24+ unit with S4 symmetry. The core of 3 consists of six fused [Mn4O4] cubanes in a 3 × 2 arrangement and linked to three additional Mn atoms at both ends. Variable-temperature, solid-state dc and ac magnetization (M) studies were carried out on complexes 1−3 in the 5.0−300 K range. Fitting of the obtained M/NμB vs H/T data by matrix diagonalization and including only axial zero-field splitting (ZFS) gave ground-state spin (S) and axial ZFS parameter (D) of S = 8, D = −0.30 cm-1 for 1, S = 7, D = −0.16 cm-1 for 2, and S = 8, D = −0.16 cm-1 for 3. The combined work demonstrates that four hydroxyethyl arms on an ethylenediamine backbone can generate novel Mn structural types not accessible with other alcohol-based ligands

A New N,N,O Chelate for Transition Metal Chemistry: Fe₅ and Fe₆ Clusters from the Use of 6-Hydroxymethyl-2,2‘-bipyridine (hmbpH)

The initial use of the anion of 6-hydroxymethyl-2,2‘-bipyridine (hmbpH) as a chelate in coordination chemistry is described. The syntheses, crystal structures, and magnetochemical characterization are reported of four new iron(III) clusters [Fe5O2(OH)(O2CMe)5(hmbp)3](ClO4)2 (1) and [Fe6O2(OH)2(O2CR)6(hmbp)4](NO3)2 (R = Ph (2), Me (3), But (4); hmbpH = 6-hydroxymethyl-2,2‘-bipyridine). The reaction of Fe(ClO4)3, hmbpH, and sodium acetate in a 1:1:∼4 ratio in EtOH gave 1, and the reaction between [Fe3O(O2CR)6(H2O)3](NO3) (R = Ph, Me, But) and hmbpH in a 1:1 ratio in MeCN gave 2−4, respectively. The core of 1 consists of a [Fe4(μ3-O)2]8+ butterfly unit to which is attached a fifth Fe atom by bridging O atoms. The core of 2−4 also consists of a [Fe4(μ3-O)2]8+ butterfly unit to which are attached an Fe atom on either side by bridging O atoms. Variable-temperature (T) and -field (H) solid-state DC and AC magnetization (M) studies were carried out on complexes 1−4 in the 5.0−300 K range. Fitting of the data revealed that 1 has an S = 5/2 ground state spin whereas 2−4 possess an S = 5 ground state. Fitting of the M/NμB vs H/T data by matrix diagonalization and including only axial zero-field splitting (ZFS) gave values of the axial ZFS parameter |D| of 0.75, 0.36, 0.46, and 0.36 cm-1 for 1−4, respectively

Unusual Structural Types in Manganese Cluster Chemistry from the Use of <i>N</i>,<i>N</i>,<i>N</i>‘,<i>N</i>‘-Tetrakis(2-hydroxyethyl)ethylenediamine: Mn₈, Mn₁₂, and Mn₂₀ Clusters

The syntheses, crystal structures, and magnetochemical characterization are reported for three new mixed-valent Mn clusters [Mn8O3(OH)(OMe)(O2CPh)7(edte)(edteH2)](O2CPh) (1), [Mn12O4(OH)2(edte)4Cl6(H2O)2] (2), and [Mn20O8(OH)4(O2CMe)6(edte)6](ClO4)2 (3) (edteH4 = (HOCH2CH2)2NCH2CH2N(CH2CH2OH)2 = N,N,N‘,N‘-tetrakis(2-hydroxyethyl)ethylenediamine). The reaction of edteH4 with Mn(O2CPh)2, MnCl2, or Mn(O2CMe)2 gives 1, 2, and 3, respectively, which all possess unprecedented core topologies. The core of 1 comprises two edge-sharing [Mn4O4] cubanes connected to an additional Mn ion by a μ3-OH- ion and two alkoxide arms of edteH22-. The core of 2 consists of a [Mn12(μ4-O)4]24+ unit with S4 symmetry. The core of 3 consists of six fused [Mn4O4] cubanes in a 3 × 2 arrangement and linked to three additional Mn atoms at both ends. Variable-temperature, solid-state dc and ac magnetization (M) studies were carried out on complexes 1−3 in the 5.0−300 K range. Fitting of the obtained M/NμB vs H/T data by matrix diagonalization and including only axial zero-field splitting (ZFS) gave ground-state spin (S) and axial ZFS parameter (D) of S = 8, D = −0.30 cm-1 for 1, S = 7, D = −0.16 cm-1 for 2, and S = 8, D = −0.16 cm-1 for 3. The combined work demonstrates that four hydroxyethyl arms on an ethylenediamine backbone can generate novel Mn structural types not accessible with other alcohol-based ligands

Unusual Structural Types in Manganese Cluster Chemistry from the Use of <i>N</i>,<i>N</i>,<i>N</i>‘,<i>N</i>‘-Tetrakis(2-hydroxyethyl)ethylenediamine: Mn₈, Mn₁₂, and Mn₂₀ Clusters

The syntheses, crystal structures, and magnetochemical characterization are reported for three new mixed-valent Mn clusters [Mn8O3(OH)(OMe)(O2CPh)7(edte)(edteH2)](O2CPh) (1), [Mn12O4(OH)2(edte)4Cl6(H2O)2] (2), and [Mn20O8(OH)4(O2CMe)6(edte)6](ClO4)2 (3) (edteH4 = (HOCH2CH2)2NCH2CH2N(CH2CH2OH)2 = N,N,N‘,N‘-tetrakis(2-hydroxyethyl)ethylenediamine). The reaction of edteH4 with Mn(O2CPh)2, MnCl2, or Mn(O2CMe)2 gives 1, 2, and 3, respectively, which all possess unprecedented core topologies. The core of 1 comprises two edge-sharing [Mn4O4] cubanes connected to an additional Mn ion by a μ3-OH- ion and two alkoxide arms of edteH22-. The core of 2 consists of a [Mn12(μ4-O)4]24+ unit with S4 symmetry. The core of 3 consists of six fused [Mn4O4] cubanes in a 3 × 2 arrangement and linked to three additional Mn atoms at both ends. Variable-temperature, solid-state dc and ac magnetization (M) studies were carried out on complexes 1−3 in the 5.0−300 K range. Fitting of the obtained M/NμB vs H/T data by matrix diagonalization and including only axial zero-field splitting (ZFS) gave ground-state spin (S) and axial ZFS parameter (D) of S = 8, D = −0.30 cm-1 for 1, S = 7, D = −0.16 cm-1 for 2, and S = 8, D = −0.16 cm-1 for 3. The combined work demonstrates that four hydroxyethyl arms on an ethylenediamine backbone can generate novel Mn structural types not accessible with other alcohol-based ligands