Formation of a steady state in the radiolysis of ferrimyoglobin in aqueous solution

The interaction of radiation-generated · OH radicals with ferrimyoglobin in deaerated aqueous solution at neutral pH has been quantitatively studied. Changes in the visible absorption spectrum have been analyzed on the basis of composition changes of the ferri, deoxy, and ferriperoxide forms of the metalloprotein. A postirradiation thermal process must be considered in order to evaluate the radical-induced composition changes. Initially, ·OH induces reduction of ferrimyoglobin to the deoxy form with a G value (molecular yield/100 eV of absorbed energy) in the zero-dose limit of 1.4 (±0.2). Radiation-generated H₂O₂ reacts with the ferrimyoglobin substrate to produce ferrimyoglobin peroxide with a G value of 0.7 (±0.1) in the zero-dose limit. At doses of >1 krad μm^?1 of myoglobin present, the composition of the three myoglobin derivatives reaches a radiolysis steady state. In this moderate-dose plateau region, this composition is 44% ferri, 18% deoxy, and 38% ferri peroxide. The · OH-induced hemoprotein radicals that do not initiate 1-eq redox conversions undergo reactions that generate dimer and other globin-modified material.     

Photosystem II: Structure and mechanism of the water:plastoquinone oxidoreductase

This mini-review briefly summarizes our current knowledge on the reaction pattern of light-driven water splitting and the structure of Photosystem II that acts as a water:plastoquinone oxidoreductase. The overall process comprises three types of reaction sequences: (a) light-induced charge separation leading to formation of the radical ion pair P680^+•Q_A^−•; (b) reduction of plastoquinone to plastoquinol at the Q_B site via a two-step reaction sequence with Q_A^−• as reductant and (c) oxidative water splitting into O₂ and four protons at a manganese-containing catalytic site via a four-step sequence driven by P680^+• as oxidant and a redox active tyrosine Y_Z acting as mediator. Based on recent progress in X-ray diffraction crystallographic structure analysis the array of the cofactors within the protein matrix is discussed in relation to the functional pattern. Special emphasis is paid on the structure of the catalytic sites of PQH₂ formation (Q_B-site) and oxidative water splitting (Mn₄O _x Ca cluster). The energetics and kinetics of the reactions taking place at these sites are presented only in a very concise manner with reference to recent up-to-date reviews. It is illustrated that several questions on the mechanism of oxidative water splitting and the structure of the catalytic sites are far from being satisfactorily answered.     

A proton magnetic relaxation study of ferrimyoglobin in aqueous ionic solutions

Proton magnetic longitudinal T₁ relaxation times have been measured for acid (horse) ferrimyoglobin solutions [0.1 M NaCl and KH₂PO₄, 2 M NaCl and 1 M MgCl₂] from 5°C to 35°C in dependence on myoglobin concentration up to 6 mM. The enhancement of the relaxation rate due to the paramagnetic haem iron. which is observed in this temperature range is compared with analogous data for the ferrihaemoglobin solution. The conclusion is that the protons exchanging from the haem pocket with bulk solvent are not those from the water molecule at the sixth ligand site of haem iron. The exchanging protons are more than 4 Å away from the haem iron being closer to it in ferrimyoglobin than in ferrihaemogiobin. This distance becomes larger in solutions with higher salt concentration, the largest difference between 0.1 M NaCl and 1 M MgCl₂ being over one Angstrom unit. This indicates a conformational change of the haem pocket, possibly its tightening.     

Magneto-structural relationships for a mononuclear Co(II) complex with large zero-field splitting

A mononuclear cobalt(II) complex, [Co(ac)₂(H₂O)₂(MeIm)₂], with heteroleptic coordination sphere possessing the {CoO₂O′₂N₂} chromophore has been prepared and structurally characterized. The magnetic data down to 2 K show an enhanced magnetic anisotropy manifesting itself in a large zero-field splitting (ZFS) parameter. As a consequence, the magnetization deviates substantially from the Brillouin-function behavior. A fit to the zero-field splitting model gave the following set of magnetic parameters: D/hc = +95 cm⁻¹, g_x = 2.530, zj/hc = −0.078, χ_TIP = 16.7 × 10⁻⁹ m³ mol⁻¹, (g_z = 2.0). The Griffith-Figgis model and the Generalized Crystal-Field model lie beyond the spin-Hamiltonian formalism; they gave analogous, although not identical ZFS parameters: D/hc = 109 cm⁻¹, and D/hc = 77 cm⁻¹, respectively. The absorption spectrum taken in the FAR-IR region exhibits manifold absorption peaks referring to the transitions among the crystal-field multiplets of the parent ⁴A_2g + ⁴E_g terms (D_4h), originating in a crystal-field splitting of the octahedral ⁴T_1g ground term.     

Synthesis, crystal structure and magnetic properties of a 1D mixed-metal-mixed-ligand Ni(II)/Fe(II) coordination polymer built on the nitroprusside anion

A new complex [Ni(L)Fe(CN)₅NO] · 2H₂O (L = 4,6,6-trimethyl-1,9-diamino-3,7-di-aza-nona-3-ene) has been obtained and characterized by means of X-ray crystallographic analysis and magnetochemistry. The Fe(CN)₅NO²⁻ anion links to the Ni(L)²⁺ cation through two bridging cyanide groups in a bent fashion. The intrachain Ni?Ni and interchain Ni?Ni distances are equal to 9.81(8) and 7.75(1) Å, respectively. The magnetic behaviour of the complex indicates the zero field splitting parameter D higher than 3 cm⁻¹ and the average exchange parameter (intra- and interchain) corresponding to direct Ni-Ni magnetic interaction in the crystal lattice equals ∼−0.2 cm⁻¹.     

Synthesis, structure and electron-mediator properties of the mono- and difunctionalized macrobicyclic iron(II) tris-dioximates with thiol terminated ribbed spacer substituents

Nucleophilic substitution of the reactive chlorine atoms of mono- and dichlorine clathrochelate FeBd₂(HGmCl)(BF)₂ and FeBd₂(Cl₂Gm)(BF)₂ precursors (where Bd²⁻, HGmCl²⁻ and Cl₂Gm²⁻ are α-benzyldioxime, chloroglyoxime and dichloroglyoxine dianions, respectively) with HSCH₂CH₂SH and (HSCH₂CH₂)₂S in the presence of triethylamine afforded the FeBd₂(HGmSCH₂CH₂SH)(BF)₂ (1) and FeBd₂(HGm(SCH₂CH₂)₂SH)(BF)₂ clathrochelates with a sole thiol terminated spacer substituent and the FeBd₂((HS(CH₂CH₂S)₂)₂Gm)(BF)₂ clathrochelate with two longchain thiol-sulfide ribbed groups. The crystal and molecular structures of these complexes were obtained by X-ray crystallography. The clathrochelate molecules possess a geometry intermediate between a trigonal prism (TP) and a trigonal antiprism (TAP). The X-ray data are in a good agreement with the ⁵⁷Fe Mössbauer parameters for complexes studied. These parameters characterize them as the low-spin iron(II) complexes (the isomeric shift values) with TP-TAP geometry (the quadrupole splitting values). Application of clathrochelate self-assembled monolayer (SAM) as the redox mediators for the determination of hydrogen peroxide is discussed. The calibration curve for hydrogen peroxide concentrations was found to be in the range from 2.0 · 10⁻⁶ to 1.6 · 10⁻⁵ mol · L⁻¹ with limit of detection equal to 1.0 · 10⁻⁶ mol · L⁻¹. The clathrochelate SAM on gold electrode provides precise and sensitive amperometric determination of hydrogen peroxide.     

The origin of split EPR signals in the Ca2+-depleted Photosystem II

A light-driven reaction model for the Ca²⁺-depleted Photosystem (PS) II is proposed to explain the split signal observed in electron paramagnetic resonance (EPR) spectra based on a comparison of EPR assignments with recent x-ray structural data. The split signal has a splitting linewidth of 160 G at around g = 2 and is seen upon illumination of the Ca²⁺-depleted PS II in the S₂ state associated with complete or partial disappearance of the S₂ state multiline signal. Another g=2 broad ESR signal with a 110 G linewidth was produced by 245 K illumination for a short period in the Ca²⁺-depleted PS II in S₁ state. At the same time a normal Y_Z^· radical signal was also efficiently trapped. The g=2 broad signal is attributed to an intermediate S₁X^· state in equilibrium with the trapped Y_Z^· radical. Comparison with x-ray structural data suggests that one of the split signals (doublet signal) is attributable to interaction between His 190 and the Y_Z^· radical, and other signals is attributable to interaction between His 337 and the manganese cluster, providing further clues as to the mechanism of water oxidation in photosynthetic oxygen evolution.     

Metal‐Free 2D/2D Heterojunction of Graphitic Carbon Nitride/Graphdiyne for Improving the Hole Mobility of Graphitic Carbon Nitride

The design and synthesis of efficient metal‐free photoelectrocatalysts for water splitting are of great significance, as nonmetal elements are generally earth abundant and environment friendly. As a typical metal‐free semiconductor, g‐C3N4 has received much attention in the field of photocatalytic water splitting. However, the poor photoinduced hole mobility of g‐C₃N₄ restrains its catalytic performance. Herein, for the first time, graphdiyne (GDY) is used to interact with g‐C₃N₄ to construct a metal‐free 2D/2D heterojunction of g‐C₃N₄/GDY as an efficient photoelectrocatalyst for water splitting. The g‐C₃N₄/GDY photocathode exhibits enhanced photocarriers separation due to excellent hole transfer nature of graphdiyne and the structure of 2D/2D heterojunction of g‐C₃N₄/GDY, realizing a sevenfold increase in electron life time (610 μs) compared to that of g‐C₃N₄ (88 μs), and a threefold increase in photocurrent density (?98 μA cm^?2) compared to that of g‐C₃N₄ photocathode (?32 μA cm^?2) at a potential of 0 V versus normal hydrogen electrode (NHE) in neutral aqueous solution. The photoelectrocatalytic performance can be further improved by fabricating Pt@g‐C₃N₄/GDY, which displays an photocurrent of ?133 μA cm^?2 at a potential of 0 V versus NHE in neutral aqueous solution. This work provides a new strategy for the design of efficient metal‐free photoelectrocatalysts for water splitting.     

The relation between the chloride status of the photosynthetic water splitting complex and the inhibitory effectiveness of amines

The protective role of chloride ions (Cl^–) against inhibition of the photosynthetic water splitting complex by amines was investigated with purified photosystem II membrane particles from tobacco chloroplasts. Seemingly competitive interactions occurred between Cl^– (except at low concentrations) and Tris, but not between Cl^– and NH₃. The rate of Cl^– release was not increased by the amines but, instead, may have been limited by a labilization under the experimental conditions of the extrinsic 23 kDa polypeptide. An additional detachment of the 18 kDa polypeptide was seen when SO₄ ^2– ions were present. Tris induced changes of the thermoluminescence patterns of flash illuminated photosystem II particles were found to be different from those caused by either Cl^– deficiency or high pH. It is concluded that the protective functions of Cl^– are brough about not because it is bound to the target site of the inhibitory actions of Lewis bases like amines and hydroxyl ions. Instead, this effect of Cl^– may be due to its influence on the tertiary and quaternary structures of the water oxidizing protein complex.     

Inactivation of the plasma membrane ATPase ofSchizosaccharomyces pombe by hydrogen peroxide and by the fenton reagent (Fe2+/H2O2): Nonradicalvs. Radical-induced oxidation

In the absence of added Fe²⁺, the ATPase activity of isolatedSchizosaccharomyces pombe plasma membranes (5–7 μmolP _i per mg protein per min) is moderately inhibited by H₂O₂ in a concentration-dependent manner. Sizable inactivation occurs only at 50–80 mmol/L H₂O₂. The process, probably a direct oxidative action of H₂O₂ on the enzyme, is not induced by the indigenous membrane-bound iron (19.3 nmol/mg membrane protein), is not affected by the radical scavengers mannitol and Tris, and involves a decrease of both theK _m of the enzyme for ATP and theV of ATP splitting. On exposing the membranes to the Fenton reagent (50 μmol/L Fe²⁺ +20 mmol/L H₂O₂), which causes a fast production of HO⁻ radicals, the ATPase is 50–60% inactivated and 90% of added Fe²⁺ is oxidized to Fe³⁺ within 1 min. The inactivation occurs only when Fe²⁺ is added before H₂O₂ and can thus bind to the membranes. The lack of effect of radical scavengers (mannitol, Tris) indicates that HO⁻ radicals produced in the bulk phase play no role in inactivation. Blockage of the inactivation by the iron chelator deferrioxamine implies that the process requires the presence of Fe²⁺ ions bound to binding sites on the enzyme molecules. Added catalase, which competes with Fe²⁺ for H₂O₂, slows down the inactivation but in some cases increases its total extent, probably due to the formation of the superoxide radical that gives rise to delayed HO⁻ production.     

Trinuclear-based coordination compounds of Mn(II) and Co(II) with 4-amino-3,5-dimethyl-1,2,4-triazole and azide and thiocyanate anions: Synthesis, structure and magnetic properties

A 2D layer complex 1 and a linear trinuclear complex 2 with mixed ligands have been synthesized and characterized by elemental analyses, IR and single-crystal X-ray diffraction. In 1, the Mn(II) ions are six-coordinated and lie in distorted octahedron coordination environments. Complex 1 is connected into a 2D layer structure based on a linear trinuclear Mn₃(admtrz)₄(N₃)₆ (admtrz = 4-amino-3,5-dimethyl-1,2,4-triazole) building unit with either (6,3) topology when Mn1 cations as three-connected nodes or (4,4) network when the coordination trinuclear units being regarded as four connected nodes. In 2, the Co(II) ions are in slightly distorted octahedron coordination geometries. The magnetic behaviors are investigated in the temperature range 1.8-300 K. The magnetic susceptibility measurements show that the Mn(II) ions of complex 1 are weakly antiferromagnetically coupled with g = 1.98(1), J1 = −6.31(5) cm⁻¹ and J2 = −1.88(1) cm⁻¹. There is dominant zero field splitting (ZFS) effects with g values, g_// = 2.38(2) and g_⊥ = 4.96(4), indicated a significant presence of the spin-orbit coupling and magnetization experiment reveals large, uniaxial zero-field splitting parameters of D = −29.55 cm⁻¹ for 2.     

On the red blood cell Ca2+-pump: An estimate of stoichiometry

Summary Efflux of Ca²⁺ from reversibly hemolyzed human red blood cell ghosts was determined by a Ca²⁺ selective electrode, by atomic absorption spectroscopy, and by the use of⁴⁵Ca. Hydrolysis of ATP was determined by measurement of inorganic phosphate (P_i). At 25°C, ghosts loaded with CaCl₂, MgCl₂, Na₂ATP, and Tris buffer (pH 7.4) extruded Ca²⁺, with mean rates ranging from 58.8±3.5 (sd) to 74.7±8.2 (sd) moles·liter ghosts^–1·min^– depending on the method of Ca²⁺ determination. The ratio of Ca²⁺ transported to P_i released in the presence of ouabain without correction for background ATP splitting was 0.83, 0.83, and 0.80, respectively, for the three methods of Ca²⁺ determination. Correction for the ATPase activity not associated with Ca²⁺ transport resulted in a ratio of 0.91:1. In other experiments, the use of La³⁺ to inhibit the Ca²⁺-pump allowed an estimate of the ATPase activity associated with Ca²⁺ extrusion. In the presence of various concentrations of La³⁺, the ratio of Ca²⁺ pumped to P_i liberated was 0.86 or 1.02, depending on the method of Ca²⁺ determination. It is concluded that the stoichiometry of the Ca²⁺-pump of the RBC plasma membrane is one Ca²⁺ pumped per ATP hydrolyzed.     

A study on mono-, bis- and tris-N-functionalized 1,4,7-triazacyclononane with benzimidazolyl groups and their nickel(II) complexes

Three new ligands, 1-(benzimidazolyl-2-methyl)-1,4,7-triazacyclononane L¹, 1,4-bis(benzimidazolyl-2-methyl)-1,4,7-triazacyclonone L², and 1,4,7-tris-(benzimidazolyl-2-methyl)-1,4,7-triazacyclonane L³, were synthesized by a straightforward one-pot method. Their nickel(II) complexes , [NiL²CH₃CN](ClO₄)₂ · 2CH₃OH · H₂O (or [NiL²Cl] · ClO₄) and [Ni(H₋₂L³)] · H₂O were obtained and characterized by electrospray mass spectrum, ¹H NMR, CV and other physical methods. Their crystal structures were determined by X-ray analyses. The crystal structure of the nickel(II) complex of L¹ shows that two Ni(II) atoms are bridged by two Cl⁻ anions. A ferromagnetic exchange coupling and zero-field splitting effect exist in complex 1.     

Synthesis and chemical characterization of Cu, Ni and Zn complexes of 3,5-bis(2′-pyridyl)-1,2,4-oxadiazole and 3-(2′-pyridyl)5-(phenyl)-1,2,4-oxadiazole ligands

The synthesis and structural characterization of Ni^II, Cu^II and Zn^II complexes of two chelating 1,2,4-oxadiazole ligands, namely 3,5-bis(2′-pyridyl)-1,2,4-oxadiazole (bipyOXA) and 3-(2′-pyridyl)5-(phenyl)-1,2,4-oxadiazole (pyOXA), is here reported. The formed hexacoordinated metal complexes are [M(bipyOXA)₂(H₂O)₂](ClO₄)₂ and [M(pyOXA)₂(ClO₄)₂], respectively (M = Ni, Cu, Zn). X-ray crystallography, ¹H and ¹³C NMR spectroscopy and C, N, H elemental analysis data concord in attributing them an octahedral coordination geometry. The two coordinated pyOXA ligands assume a trans coplanar disposition, while the two bipyOXA ligands are not. The latter result is a possible consequence of the formation of H-bonds between the coordinated water molecules and the nitrogen atom of the pyridine in position 5 of the oxadiazole ring. The expected splitting of the d metal orbitals in an octahedral ligand field explains the observed paramagnetism of the d⁸ and d⁹ electron configuration of the nickel(II) and copper(II) complexes, respectively, as determined by the broadening of their NMR spectra.     

Optical properties of a novel neodymium pentafluoropropionate binuclear complex

A novel neodymium pentafluoropropionate binuclear complex, Nd(C₂F₅COO)₃Dipy (Dipy: 2,2′-dipyridyl), was synthesized and characterized by single-crystal X-ray diffraction. At a concentration of 0.2 M in DMSO-d₆, the Judd-Ofelt parameters (Ω₂, Ω₄, Ω₆) were calculated from the UV-Vis spectrum. According to the small value of Ω₂ and the zero splitting energy of ⁴F/_3/2 level, a symmetric ligand field of the complex was confirmed in DMSO-d₆. Strong emission of the complex in DMSO-d₆ at 1057 nm with a decay time about 1.3 μs were detected when excited at 800 nm pumped by a laser diode. The stimulated emission cross-section of ⁴F_3/2 → ⁴I_11/2 fluorescence transition was 2.36 × 10⁻²⁰ cm² and comparable with some laser glasses, which indicated good radiative properties of this neodymium pentafluoropropionate binuclear complex in liquid matrix.     

A cyano-bridged FeRe(CN)2 cluster incorporating two high-magnetic anisotropy building units

The pentagonal bipyramidal high-spin iron(II) complex, [(TPA^2C(O)NHtBu)Fe(CF₃SO₃)]⁺, is shown to exhibit a high-anisotropy ground state, with fits to dc magnetization data providing an axial zero-field splitting parameter of D = − 7.9 cm⁻¹. The utility of this compound as a building unit is demonstrated, as its reaction with [ReCl₄(CN)₂]²⁻ affords the cyano-bridged dinuclear cluster (TPA^2C(O)NHtBu)FeReCl₄(CN)₂. dc magnetic susceptibility measurements reveal intracluster ferromagnetic exchange interactions between Fe^II and Re^IV centers, with J = +3.0 cm⁻¹, giving rise to a spin ground state of S = 7/2. Moreover, fits to dc magnetization data obtained for the FeRe cluster show the presence of strong axial anisotropy, with D = −2.3 cm⁻¹. Finally, variable-frequency ac susceptibility measurements reveal the onset of slow magnetic relaxation at low temperature, suggesting that the FeRe cluster is a single-molecule magnet.     

Seven-coordinate Mn(II) and Co(II) complexes of the pentadentate ligand 2,6-diacetyl-4-carboxymethyl-pyridine bis(benzoylhydrazone): Synthesis, crystal structure and magnetic properties

The metal complexation properties of a functionalized N₃O₂ donor ligand H₂L², where H₂L² stands for 2,6-diacetyl-4-carboxymethyl-pyridine bis(benzoylhydrazone), are investigated by structural and spectroscopic (IR, ESI-MS and EPR) characterization of its Mn(II) and Co(II) complexes. The ligand H₂L² is observed to react essentially in the same fashion as its unmodified parent H₂L¹ producing mixed-ligand [M(H₂L²)(Cl₂)] complexes (M = Mn^II (1), Co^II (3)) upon treatment with MCl₂. Complexes [M(HL²)(H₂O)(EtOH)]BPh₄ (M = Mn 2, M = Co 4), incorporating the supporting ligand in the partially deprotonated form (HL²)⁻, are formed by salt elimination of the [M(H₂L²)(Cl₂)] compounds with NaBPh₄. Compounds 2 and 4 are isostructural featuring distorted pentagonal-bipyramidal coordinated Mn^II and Co^II ions, with the H₂O and EtOH ligands bound in axial positions. Intermolecular hydrogen bonding interactions of the type M-OH₂?O-M involving the H₂O ligands and the carbonyl functions of the supporting ligand assembles the complexes into dimers. Temperature-dependent magnetic susceptibility measurements (2-300 K) show a substantially paramagnetic Curie behavior for the Mn²⁺ compound (2) influenced by zero-field splitting and significant orbital angular momentum contribution for 4 (high-spin Co^II). The exchange coupling across the Mn^II-OH₂?O-Mn^II bridges in 2 was found to be less than 0.1 cm⁻¹, suggesting that no significant intradimer exchange coupling occurs via this path.     

Synthesis, structure and characterization of new complexes [Fe2(μ-OMe)2(PAP)(X)4] (PAP= 1,4-di(2-pyridyl)aminophthalazine, X=Cl, OAc) and their oxidation catalysis

Two dinuclear iron(III) complexes with tetradentate N-donor ligand 1,4-di(2^′-pyridyl)aminophthalazine (PAP), [Fe₂(μ-OMe)₂(PAP)Cl₄] (2) and [Fe₂(μ-OMe)₂(PAP)(OAc)₄] (3) were prepared and characterized. Single crystal X-ray molecular structure of [Fe₂(μ-OMe)₂(PAP)Cl₄] · 2MeOH have been elucidated. The six-coordinate iron atoms are in distorted octahedral environment bridged by the oxygen atoms of two methoxy groups and the PAP ligand. The Mössbauer spectra of both complexes show one quadrupole doublet and the isomer shift and quadrupole splitting values indicate the presence of octahedral high-spin Fe^III ions. Complex 2 showed catalytic activity for alkane oxidation with hydrogen peroxide.     

Crystal structure and luminescence properties of the blue‐green‐emitting Ba9(Lu,Y)2Si6O24:Ce3+ phosphor

Samples of the Ba₉(Lu_2‐xY_x)Si₆O₂₄:Ce³⁺ (x = 0–2) blue‐green phosphors were synthesized by solid‐state reactions. All the samples exhibited a rhombohedral crystal structure. As the Y³⁺ concentration increased, the diffraction peaks shifted to the small angle region and the lattice parameters increased due to the larger ionic radius of Y³⁺ (r = 0.900 Å) compared with that of Lu³⁺ (r = 0.861 Å). Under 400 nm excitation, samples exhibited strong blue‐green emissions around 490 nm. The emission bands had a slight blue shift that resulted from weak crystal‐field splitting with increasing Y³⁺ concentration. Luminescence intensity and quantum efficiency (QE) decreased with increasing Y³⁺ concentration. The internal QE decreased from 74 to 50% and the external QE decreased from 50 to 34% as x increased from 0 to 2. The thermal stability of the Lu series was better than that of the Y‐series. The excitation band peak around 400 nm matched well with the emission light from the efficient near‐ultraviolet (NUV) chip. These results indicate promising applications for these NUV‐based white light‐emitting diodes.     

Antiferromagnetic interactions through phenoxo bridges and lattice water: Synthesis, structure, and magnetic properties of new Mn(III) Schiff base complexes in combination with thiocyanate ligand

The Schiff base ligands, N,N′-bis(2-hydroxyacetophenone)-1,2-diaminoethane (acphenH₂) and N,N′-bis(2-hydroxyacetophenone)-1,3-diaminopropane (acphpnH₂), prepared in situ were used to synthesise two new Mn(III) complexes which were characterised by crystallography and variable temperature magnetic measurements. [Mn(acphen)NCS]₂ is a phenoxo-bridged dimeric compound with the thiocyanate coordinating in the usual bent mode (Mn-N-C angle, 152°) and is weakly antiferromagnetic. Since there are no significant inter-dimer contacts in the crystal, the low temperature magnetic behaviour is influenced by single ion zero-field splitting. Exact diagonalisation of the spin Hamiltonian was performed to derive the following parameters: J = −0.7 cm⁻¹, D = −0.6 cm⁻¹. Mn(acphpn)(H₂O)NCS is monomeric with an unusual linearly coordinated thiocyanate (Mn-N-C angle, 178°). Two lattice water molecules link the Mn(III) complex molecules through hydrogen bonds to form one-dimensional chains in the crystal. Magnetic exchange along the chain makes this compound also weakly antiferromagnetic with J ∼ -2 cm⁻¹.