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To examine how small structural changes influence the reactivity and magnetic properties of biologically relevant metal complexes, the reactivity and magnetic properties of two structurally related five-coordinate Fe(III) thiolate compounds are compared. (Et,Pr)-ligated [Fe(III)(S(2)(Me2)N(3)(Et,Pr))]PF(6) (3) is synthesized via the abstraction of a sulfur from alkyl persulfide ligated [Fe(III)(S(2)(Me2)N(3)(Et,Pr))-S(pers)]PF(6) (2) using PEt(3). (Et,Pr)-3 is structurally related to (Pr,Pr)-ligated [Fe(III)(S(2)(Me2)N(3)(Pr,Pr))]PF(6) (1), a nitrile hydratase model compound previously reported by our group, except it contains one fewer methylene unit in its ligand backbone. Removal of this methylene distorts the geometry, opens a S-Fe-N angle by approximately 10 degrees, alters the magnetic properties by stabilizing the S = 1/2 state relative to the S = 3/2 state, and increases reactivity. Reactivity differences between 3 and 1 were assessed by comparing the thermodynamics and kinetics of azide binding. Azide binds reversibly to both (Et,Pr)-3 and (Pr,Pr)-1 in MeOH solutions. The ambient temperature K(eq) describing the equilibrium between five-coordinate 1 or 3 and azide-bound 1-N(3) or 3-N(3) in MeOH is approximately 10 times larger for the (Et,Pr) system. In CH(2)Cl(2), azide binds approximately 3 times faster to 3 relative to 1, and in MeOH, azide dissociates 1 order of magnitude slower from 3-N(3) relative to 1-N(3). The increased on rates are most likely a consequence of the decreased structural rearrangement required to convert 3 to an approximately octahedral structure, or they reflect differences in the LUMO (vs SOMO) orbital population (i.e., spin-state differences). Dissociation rates from both 3-N(3) and 1-N(3) are much faster than one would expect for low-spin Fe(III). Most likely this is due to the labilizing effect of the thiolate sulfur that is trans to azide in these structures.

Tetraphenylporphinatomanganate(III) tetracyanoethenide, [MnTPP][TCNE], is the prototype of a growing family of linear chain (1-D) coordination polymers that magnetically order as ferrimagnets. [MnTPP][TCNE]·xS [S = PhMe (x = 2), 1,2-C6H4Me2 (x = 1), 1,2-C6H4Cl2 (x = 3), 1,2,4-C6H3Cl3 (x = 2), and 1,3-C6H4Cl2 (x = 2)] have been prepared and structurally and magnetically characterized. All form 1-D chain structures with intrachain Mn···Mn separations ranging from 9.202 to 10.218 A. The 173 K crystal structure of [MnTPP][TCNE]·2PhMe has been rerefined, revealing that the [TCNE]•- is 2-fold-disordered and coordinated to MnIII by a pair of trans cyano nitrogen atoms to form parallel one-dimensional chains. The two orientations of [TCNE]•- are related by a 180° rotation about the diagonal axis joining the trans nitrogen atoms bound to MnIII. The major form has an occupancy of 83.3(4)% with a Mn−NTCNE distance of 2.328(3) A and a MnNC angle of 146.8(8)°. The minor form, with 16.7(4)% occupancy, has a Mn−NTCNE di...

A series of four structurally related cis-dithiolate-ligated Fe(III) complexes, [Fe(III)(DITpy)2]Cl (1), [Fe(III)(DITIm)2]Cl (2), [Fe(III)(ADIT)2]Cl (3), and [Fe(III)(AMIT)2]Cl (4), are described. The structural characterization of 3 as well as the spectroscopic properties of 3 and 4 has been previously reported. Crystal data for 1, 2, and 4 are as follows: 1.3H2O crystallizes in the orthorhombic space group Pca2(1) with a = 19.800(4) A, b = 18.450(4) A, c = 14.800(3) A, and Z = 8. 2.(1/2)EtOH.1/2H2O crystallizes in the monoclinic space group Cc with a = 24.792(4) A, b = 14.364(3) A, c = 17.527(3) A, beta = 124.91(2) degrees, and Z = 8. 4 crystallizes in the triclinic space group P1 with a = 8.0152(6) A, b = 10.0221(8) A, c = 11.8384(10) A, alpha = 73.460(3) degrees, beta = 71.451(5) degrees, gamma = 72.856(4) degrees, and Z = 2. Complexes 1-4 share a common S2N4 coordination environment that consists of two cis-thiolates, two trans-imines, and two cis-terminal nitrogen donors: Nterm = pyridine (1), imidazole (2), and primary amine (3 and 4). The crystallographically determined mean Fe-S bond distances in 1-4 range from 2.196 to 2.232 A and are characteristic of low-spin Fe(III)-thiolate complexes. The low-spin S = 1/2 ground state was confirmed by both EPR and magnetic susceptibility measurements. The electronic spectra of these complexes are characterized by broad absorption bands centered near approximately 700 nm that are consistent with ligand-to-metal charge-transfer (CT) bands. The complexes were further characterized by cyclic voltammetry measurements, and all possess highly negative Fe(III)/Fe(II) redox couples ( approximately -1 V vs SCE, saturated calomel electrode) indicating that alkyl thiolate donors are effective at stabilizing Fe(III) centers. Both the redox couple and the 700 nm band in the visible spectra show solvent-dependent shifts that are dependent upon the H-bonding ability of the solvent. The implications of these results with respect to the active site of the iron-containing nitrile hydratases are also discussed.

The reaction of hexacyanobutadiene (HCBD) and meso-tetrakis(4-chlorophenyl)porphinatomanganese(II) pyridine [MnIITClPPpy] (1Cl) leads to two phases of [MnIIITClPPpy][HCBD].PhMe (alpha-2Clpy, beta-2Clpy). Similarly, the reaction of HCBD and tetrakis(4-bromophenyl)porphinatomanganese(II) pyridine [MnIITBrPPpy] (1Br) leads to two products [MnIIITBrPPpy] [HCBD] * PhMe (2 Brpy) and [MnIIITBrPP][HCBD]*2 PhMe (3Br). The structure of dark-green alpha-2Clpy consists of one porphyrin unit with MnIII in a square pyramidal coordination environment axially bound to one pyridine. The cation forms [MnIIITCIPPpy](2)2+ as cofacial dimerized porphyrins. Each [HCBD]*- is nonplanar with a torsion angle of 170.8(4) degrees about the center C-C bound, and forms [HCBD](2)2- dimers in the solid state with sub-van der Waals contacts of 3.325 and 3.340 angstroms. The magnetic data above 10 K obey the Curie-Weiss expression with a theta of -2.5 K, and mueff (300 K) = 4.91 muB as expected for S=2MnIII and S = 0 [HCBD](2)2-. The magnetic data for alpha-2Clpy can be fit with an zero-field-splitting D of -1.45 K. beta-2 Clpy consists of one porphyrin unit with MnIII in a distorted octahedral coordination environment axially bound to py and to a monodentate [HCBD]*- bound via an exo-nitrile. [HCBD]*- is nonplanar with a torsion angle of 169.7(5) degrees about the center C-C bound. The ueff (350 K) is 5.09 muB; however, the magnetic data do not obey the Curie-Weiss expression above 70 K. The low temperature data may be fit with a theta of -5.4 K. The data was modeled to an isolated S = 2 and S = 1/2 dinuclear spin system with J/kappaB = - 90 K. Decomposition of [HCBD]*- to [C4(CN)5O]- was evidenced by the determination of the structure of [MnIIITCIPP][C4(CN)5O] 2PhMe (3ClO). Crystals of 3 Cl-O were prepared by reaction of HCBD and 1Cl in the presence of a drop of water. The molecular structure consists of [HCBD]*-trans-mu-N-2,3-bound to [MnIIITBrPP]+ forming a 1-D coordination polymer of alternating [MnIIITBrPP]+ and [HCBD]*-. The intrachain Mn***Mn distance was 10.675(3) angstroms, with important interchain Mn***Mn distances of 10.832, 11.016, and 14.696 A. The magnetic data were fit to a Curie-Weiss law (10 < T< 290 K) with a theta of -3.5 K, and D = 0.3 K with mueff = 4.97 muB at 300 K.

5,10,15,20-Tetrakis(4-fluorophenyl)porphyrinatomanganese(III) tetracyanoethenide, [MnTFPP][TCNE], 1F, 5,10,15,20-tetrakis(4-bromophenyl)porphyrinatomanganese(III) tetracyanoethenide, [MnTBrPP][TCNE], 1Br, and 5,10,15,20-tetrakis(4-iodophenyl)porphyrinatomanganese(III) tetracyanoethenide, [MnTIPP][TCNE], 1I, have been prepared and characterized as both the toluene and dichloromethane disolvates and the magnetic, IR, and thermal properties of these solvates, as well as their corresponding desolvated materials, have been determined and are compared to the previously reported [TCNE]˙− salts of 5,10,15,20-tetrakis(4-chlorophenyl)porphyrinatomanganese(III), 1Cl. The νCN absorptions of 1X·2PhMe (X = Cl, Br, I) and 1I·xxCH22Cl22 occur at 2202 ± 1 (m) and 2161 ± 1 (s) cm−1 and 1X·xxCH22Cl22 (X = F, Cl, Br) and 1F·xxPhMe occur at 2195 ± 1 (m) and 2135 ± 2 (s) cm−1. Upon thermolysis at 175 °C the toluene desolvates to form α-[MnTXPP][TCNE] [X = Cl (α-1C1), Br (α-1Br), I (α-1I)] with νCN absorptions maintained at 2201 ± 1 (m) and 2160 ± 1 (s) cm−1. In contrast, unlike 1Cl·2PhMe, desolvation of 1X·2PhMe (X = Br, I) in refluxing n-octane (127 °C) or heated mineral oil (170 °C) slurries does not lead to materials with νCN absorptions characteristic of β-[MnTClPP][TCNE]. Upon facile desolvation of dichloromethane solvates, materials with νCN absorptions characteristic of γ-[MnTClPP][TCNE] form as the νCN absorptions remain essentially unchanged [2195 ± 2 (m) and 2135 ± 2 (s) cm−1]. The magnetic data for the [MnTXPP][TCNE] family are consistent with linear chain ferrimagnets comprised of antiferromagnetically coupled S = 2 MnIII sites and S = 1/2 [TCNE]˙− sites with the antiferromagnetic intrachain coupling, Jintra/kB (kB = Boltzmann’s constant) determined from fits to the Seiden expression for isolated chains comprised of alternating S = 1/2 and S = 2 spins. For the [MnTFPP][TCNE] series, Jintra values of −225, −160, −210, and −177 K were obtained for 1F·xxPhMe, β-1F, 1F·2CH22Cl22, and γ-1F, respectively. While Jintra values of −30, −45, −270, and −75 K were observed for 1Br·2PhMe, α-1Br, 2CH22Cl22, and γ-1Br, respectively. Finally, Jintra values of −53, −35, −35, and −53 K were observed for 1I·2PhMe, α-1I, 1I·2CH22Cl22, and γ-1I, respectively. The ordering temperatures, Tc, determined from the maxima in the 10 Hz χ′(T) ranged from 6.5 K (1I·2PhMe) to 28 K for (1F·xxPhMe). Based on the magnetic behavior, desolvation of 1X·PhMe and 1X·CH22Cl22 increases the magnetic disorder and subsequent spin glass behavior as well as changing the observed interchain magnetic coupling.

The magnetic susceptibility (χ) of 1,6,10,15,19,25,28,32-octa-n-butoxynaphthalocyaninatomanganese(III) tetra-cyanoethanide can be fit to a Curie–Weiss expression with θ = 54 K for T > 150 K, and the χT(T) data are con-sistent with linear chains and can be fit to a Seiden expression for alternating S = 2 and S = 1/2 anti-ferromagnetically coupled spin sites with a coupling constant, Jintra/kB (H = −2JSa·Sb) of −145 K. Hysteresis with a coercive field of 1.6 kOe was observed at 2 K. The magnetic ordering temperature, Tc, determined from both the maximum in the 10 Hz ac susceptibility, χ′(T), and the irreversibility of low field zero field cooled/field cooled magnetization data, was determined to be 9.0 K. This is the first example of a metallophthalocyanine electron transfer salt that magnetically orders.

The quest to identify a new molecule-based magnet led to the discovery that the reduction of meso-tetrakis(pentafluorophenyl)porphyrinatomanganese(iii) chloride, MnIIITF5PPCl, with sodium borohydride and its subsequent reaction with tetracyanoethylene (TCNE) forms the magnet [MnIIITF4OMePP][tcne]. The structure undergoes a reversible phase transition (see picture) below −100 °C, which is not evident from either the magnetic or infrared data.

(meso-Tetrakis(4-chlorophenyl)porphinato)manganese(III) tetracyanoethenide, [MnTClPP][TCNE], has been prepared and structurally characterized as the toluene and dichloromethane disolvates, and the magnetic and thermal properties of these solvates, as well as their corresponding desolvates, have been determined.

Nitrile hydratase (NHase) is an iron-containing metalloenzyme that converts nitriles to amides. The mechanism by which this biochemical reaction occurs is unknown. One mechanism that has been proposed involves nucleophilic attack of an Fe-bound nitrile by water (or hydroxide). Reported herein is a five-coordinate model compound ([Fe(III)(S(2)(Me2)N(3)(Et,Pr))](+)) containing Fe(III) in an environment resembling that of NHase, which reversibly binds a variety of nitriles, alcohols, amines, and thiocyanate. XAS shows that five-coordinate [Fe(III)(S(2)(Me2)N(3)(Et,Pr))](+) reacts with both methanol and acetonitrile to afford a six-coordinate solvent-bound complex. Competitive binding studies demonstrate that MeCN preferentially binds over ROH, suggesting that nitriles would be capable of displacing the H(2)O coordinated to the iron site of NHase. Thermodynamic parameters were determined for acetonitrile (DeltaH = -6.2(+/-0.2) kcal/mol, DeltaS = -29.4(+/-0.8) eu), benzonitrile (-4.2(+/-0.6) kcal/mol, DeltaS = -18(+/-3) eu), and pyridine (DeltaH = -8(+/-1) kcal/mol, DeltaS = -41(+/-6) eu) binding to [Fe(III)(S(2)(Me2)N(3)(Et,Pr))](+) using variable-temperature electronic absorption spectroscopy. Ligand exchange kinetics were examined for acetonitrile, iso-propylnitrile, benzonitrile, and 4-tert-butylpyridine using (13)C NMR line-broadening analysis, at a variety of temperatures. Activation parameters for ligand exchange were determined to be DeltaH(+ +) = 7.1(+/-0.8) kcal/mol, DeltaS(+ +) = -10(+/-1) eu (acetonitrile), DeltaH(+ +) = 5.4(+/-0.6) kcal/mol, DeltaS(+ +) = -17(+/-2) eu (iso-propionitrile), DeltaH(+ +) = 4.9(+/-0.8) kcal/mol, DeltaS(+ +) = -20(+/-3) eu (benzonitrile), and DeltaH(+ +) = 4.7(+/-1.4) kcal/mol DeltaS(+ +) = -18(+/-2) eu (4-tert-butylpyridine). The thermodynamic parameters for pyridine binding to a related complex, [Fe(III)(S(2)(Me2)N(3)(Pr,Pr))](+) (DeltaH = -5.9(+/-0.8) kcal/mol, DeltaS = -24(+/-3) eu), are also reported, as well as kinetic parameters for 4-tert-butylpyridine exchange (DeltaH(+ +) = 3.1(+/-0.8) kcal/mol, DeltaS(+ +) = -25(+/-3) eu). These data show for the first time that, when it is contained in a ligand environment similar to that of NHase, Fe(III) is capable of forming a stable complex with nitriles. Also, the rates of ligand exchange demonstrate that low-spin Fe(III) in this ligand environment is more labile than expected. Furthermore, comparison of [Fe(III)(S(2)(Me2)N(3)(Et,Pr))](+) and [Fe(III)(S(2)(Me2)N(3)(Pr,Pr))](+) demonstrates how minor distortions induced by ligand constraints can dramatically alter the reactivity of a metal complex.

1H NMR line-shape measurements have been performed in the linear chain molecule-based ferrimagnet [MnTFPP][TCNE].xPhMe (TFPP=tetrakis(4-fluorophenyl)porphinato; TCNE=tetracyanoethylene) as a function of temperature. Hyperfine shifts of opposite sign were observed indicating the presence of two oppositely hyperfine couplings, predominantly between the Mn ions and the 1 H nuclei of the planar ring of the [MnTFPP] + unit. The observation of the hyperfine shifts strongly suggests the existence of two oppositely directed [MnTFPP] + sites. Since there is no direct exchange coupling between adjacent [MnTFPP] spins, then it can be argued that an ordered spin configuration with antiparallel components may arise from antisymmetric spin-spin exchange interactions. The field independence of the hyperfine shifts at low temperatures and for applied magnetic fields in the range 2-5 T, indicates the presence of ferromagnetic interactions in the ground state of the ferrimagnetic chain.

The toluene solvates of meso-tetrakis(4-halophenyl)porphinatomanganese(III) tetracyanoethenide, [MnTFPP][TCNE] (1F), [MnTBrPP][TCNE] (1Br), and [MnTIPP][TCNE] (1I) have been prepared, and the magnetic and thermal properties have been determined and compared to those of [MnTClPP][TCNE] (1Cl). 1Br and 1I form uniform 1-D chains with each [TCNE](*)(-) being trans-m-N-sigma-bound to Mn(III) with Mn-N distances of 2.293 (1Br) and 2.276 (1I), which are a bit longer than 2.267 A observed for 1Cl. The Mn-N-C angles are 167.2, 168.1, and 158.7, while intrachain Mn.Mn separations are 10.189, 10.277, and 10.101 A. The magnetic susceptibilities for 1Br and 1I can be fit by the Curie-Weiss expression with high-temperature (T > 200 K) theta and low-temperature (T < 110 K) effective theta' values of -53 and 13 K and -79 and 30 K, respectively, compared to -60 and 13 K in 1Cl. theta is not observed for 1F; however, theta' is 70 K. The magnetic data are consistent with linear chain ferrimagnets composed of antiferromagnetically coupled S = 2 Mn(III) sites and S = (1)/(2) [TCNE](*)(-) sites with the antiferromagnetic intrachain coupling, J(intra/)k(B) (k(B) = Boltzmann's constant) determined from fits to the Seiden expression, of -225, -33, -30, and -53 K for the 1F, 1Cl, 1Br, and 1I, respectively. Hysteresis with coercive fields at 2 K of 20.0, 6.7, 4.0, and 15.9 kOe was observed for the 1F, 1Cl, 1Br, and 1I, respectively. Metamagnetic behavior is observed below 10 K for 1F, and below 5 K for both 1Br and 1I. The observed critical fields of 21.8, 6.8, 4.1, and 15.8 kOe were observed for 1F, 1Cl, 1Br, and 1I at 2 K, respectively. The ordering temperatures, T(c), determined from the maxima in the chi'(T) data taken at 10 Hz, are 28.0, 8.8, 8.0, and 6.5 K for 1F, 1Cl, 1Br, and 1I, respectively. The 28 K T(c) for 1F is the highest reported for this family of magnets.

The reaction of GdPc2 and the strong electron acceptor C4(CN)6 forms [GdPc2][C4(CN)6], which is formulated as [GdIII(Pc•-)2]+[C4(CN)6]•- with four paramagnetic centers.