Trigonal Pyramidal Coordination Geometry Research Articles

Silver(I) complexes based on diorganoselenium(II) ligands with amino or hydroxo functionalities

The diorganoselenide [Me2C(OH)CH2]2Se (1) was prepared by reacting the in situ obtained Na2Se with 1‐chloro‑2‐methyl‐2‐propanol. Reactions of 1 and [2-(Me2NCH2)C6H4]2Se (2) with appropriate silver(I) salts in 1:1 molar ratio resulted in metal complexes of type [Ag(X)Se{CH2C(OH)Me2}2] [X = OSO2CF3 (OTf) (3), OClO3 (4)] and [Ag(X)Se{C6H4(CH2NMe2)-2}2] [X = OSO2CF3 (5), ONO2 (6)], respectively. The ligand 1 and the silver complexes were investigated by appropriate spectroscopic methods, both in solution and in solid state: multinuclear NMR (1H, 13C, 19F, 77Se), ESI+ mass spectrometry, IR spectroscopy and molar conductivity. The metal complexes behave as 1:1 electrolytes in 10−3 MeOH solutions, while in solid state the anionic ligands behave as monodentate moieties. Complexes 4 and 5 were investigated by single‐crystal X‐ray diffraction. The crystal of 4 contains two similar independent molecules, 4a and 4b, for which was observed the migration of one OH hydrogen from ligand 1 to the OClO3 group, thus resulting in [Ag(HClO4)Se{OCCH2Me2}{(OH)CCH2Me2}], where ligand 1 behaves as an O,Se monometallic biconective moiety. In 5 the ligand 2 acts as a N,Se,N monometallic triconective moiety. In both compounds Ag(I) is surrounded by the donor atoms in a trigonal pyramidal coordination geometry. Strong Se→Ag intermolecular interactions in 4 resulted in 1D coordination polymers built by 4a and 4b molecules, respectively, while in the crystal of 5 no interaction between heavy atoms was observed. Supramolecular networks based on H‧‧‧O contacts are formed in both compounds.

Efficient photocatalytic water reduction by a cobalt(ii) tripodal iminopyridine complex

Enhanced reactivity is observed in a cobalt tripodal iminopyridine WRC bearing a metal active site with a trigonal pyramidal coordination geometry.

Synthesis, Structure, and Reactivity of Low-Spin Cobalt(II) Imido Complexes [(Me3P)3Co(NAr)

The reactions of [Co(PMe3)4] with the bulky organic azides, DippN3 and DmpN3 [Dipp, 2,6-diisopropylphenyl; Dmp, 2,6-di(2',4',6'-trimethylphenyl)phenyl], afforded the cobalt(II) terminal imido complexes [(Me3P)3Co(NAr)] (Ar = Dipp, 1; Dmp, 2). The cobalt imido complexes in their solid states show trigonal pyramidal coordination geometry and long Co-N(imido) separations (ca. 1.71 Å). Spectroscopic characterization and theoretical studies indicated their low-spin cobalt(II) nature. Reactivity studies on 1 revealed its nitrene-transfer reactions with PMe3 and CO, the imido/oxo and imido/sulfido exchange reactions with PhCHO and CS2, and the single-electron oxidation reaction by ferrocenium cation to form cobalt(III) imide.

Synthesis, Crystal Structure, and Electroconducting Properties of a 1D Mixed-Valence Cu(I)–Cu(II) Coordination Polymer with a Dicyclohexyl Dithiocarbamate Ligand

A new mixed-valence Cu(I)–Cu(II) 1D coordination polymer, [CuI4CuIIBr4(Cy2dtc)2]n, with an infinite chain structure is synthesized by the reaction of Cu(Cy2dtc)2 (Cy2dtc− = dicyclohexyl dithiocarbamate, C13H22NS2) with CuBr·S(CH3)2. The as-synthesized polymer consists of mononuclear copper(II) units of CuII(Cy2dtc)2 and tetranuclear copper(I) cluster units, CuI4Br4. In the cluster unit, all the CuI ions have distorted trigonal pyramidal coordination geometries, and the CuI–CuI or CuI–CuII distances between the nearest copper ions are shorter than the sum of van der Waals radii for Cu–Cu.

Crystal structure of bromido-bis-(naph-thal-en-1-yl)anti-mony(III).

In the title compound, [SbBr(C10H7)2], the SbIII atom has a distorted trigonal–pyramidal coordination geometry and the planes of the two naphthalene ring systems make a dihedral angle of 80.26 (18)°. An intra­molecular C—H⋯Br hydrogen bond forms an S(5) ring motif. In the crystal, weak C—H⋯Br inter­actions link the mol­ecules into helical chains along the b-axis direction.

Organoantimony(III) and -bismuth(III) hypervalent pseudohalides. An experimental and theoretical study

The reaction between the organopnicogen(III) chlorides R2MCl and RMCl2 [M = Sb, Bi; R = 2-(Me2NCH2)C6H4] and alkali metal pseudohalides in a 1:1 and a 1:2 molar ratio, respectively, resulted in the formation of hypervalent species of type R2MX (M = Sb, X = NCO (1), NCS (2) and SeCN (3), M = Bi, X = NCO (4) and SeCN (5), and RMX2 (M = Sb, X = NCO (6) and NCS (7), M = Bi, X = NCO (8), NCS (9) and SeCN (10). The new species were characterized by multinuclear NMR (1H, 13C, 77Se where appropriate), IR spectroscopy and mass spectrometry. The molecular structures of compounds 2–5 and 7 were determined by single-crystal X-ray diffraction. In all five compounds the nitrogen atoms in the pendant arms are involved in intramolecular coordination to metal, thus resulting in a distorted square pyramidal coordination geometry (12-M-5 hypervalent species) in case of 2–5 and a distorted trigonal pyramidal coordination geometry in case of 7 (10-Sb-4 hypervalent species). The intramolecular N → M coordination determines a chiral pattern of the investigated compounds. Bi⋯Phcentroid intermolecular interactions led to dimers in case of compound 4. In all species weak CH⋯Phcentroid intermolecular contacts led to polymeric associations, e.g. polymeric chains in case of compounds 2, 3, 5 and 7 and a 2D layer structure built by chains of dimers in case of compound 4. DFT calculations and FTIR data allowed us to assign the coordination pattern of the pseudohalide ligand in the other species.

Tris(μ4-azepane-1-carbodithioato)bis(μ3-azepane-1-carbodithioato)-μ9-bromido-tetra-μ2-bromido-octacopper(I)copper(II)

The reaction of Cu(Hm-dtc)2 (H2m-dtc is azepane-1-carbodi­thioic acid), CuBr2 and methyl iso­thio­cyanate yielded the title mixed-valence nona­nuclear CuI/CuII compound, [Cu9Br5(C7H12NS2)5] or [CuI 8CuIIBr5(Hm-dtc)5], encapsulating a bromide anion in the center of the Cu9Br4S10 cluster cage. The cage consists of a mononuclear CuII unit [Cu(Hm-dtc)2], three μ4-bridging Hm-dtc− ligands, eight CuI ions with distorted tetra­hedral or trigonal pyramidal coordination geometries and four μ2-bridging bromide anions. The incorporated central bromide anion inter­acts with nine Cu ions with shorter Cu—Br separations than the sum of the van der Waals radii for Cu and Br.

Structural characterization of tris(pyrazolyl)hydroborato and tris(2-pyridylthio)methyl lithium compounds: Lithium in uncommon trigonal pyramidal and trigonal monopyramidal coordination environments

X-ray diffraction reveals that the molecular structures of the tris(pyrazolyl)hydroborato and tris(2-pyridylthio)methyl lithium compounds, [TpBut,R]Li (R=H, Me) and [κ4-Tptm]Li, respectively exhibit three-coordinate trigonal pyramidal and four-coordinate trigonal monopyramidal coordination geometries, both of which are uncommon for lithium. Accordingly, [TpBut]Li and [TpBut,Me]Li bind additional ligands to form four-coordinate adducts, such as [TpBut]Li(NCMe), [TpBut,Me]Li(NCMe), [TpBut]Li(pzButH), [TpBut,Me]Li(pzButH)·(pzButH), [TpBut,Me]Li(OH2), [TpBut,Me]Li(OH2)·(pzH) and [TpBut]Li(OH2)·(THF), each of which has been structurally characterized by X-ray diffraction in the solid state. In solution, however, dissociation of the ligand (L) from the adducts [TpBut,R]LiL is facile such that the adducts exist in equilibrium with [TpBut,R]Li and L, as demonstrated by NMR spectroscopic studies.

Isolation and X-ray structures of four Rh(PCP) complexes including a Rh(I) dioxygen complex with a short O–O bond

The reaction of RhCl3·H2O with tBu2P(CH2)5PtBu2 afforded several complexes including [RhIII(H)Cl{tBu2P(CH2)2CH(CH2)2PtBu2}] (1), [RhIIIHCl2{tBu2P(CH2)5PtBu2}]2 (2), [RhICl{tBu2P(CH2)2CHCHCH2PtBu2}] (3) and [RhICl{tBu2PCH2C(O)CHCHCH2PtBu2}] (4). X-ray crystal structures of 3 and 4 showed that the CC bond on the C5 unit of tBu2P(CH2)5PtBu2 is bound to Rh(I) in a η2 configuration. In 4, the Rh atom has a trigonal pyramidal coordination geometry. The X-ray crystal structure of 2 consists of two rhodium(III) centers bridged by two tBu2P(CH2)5PtBu2 ligands with two phosphorus atoms, one from each ligand, trans to one another. The crystal structure of the rhodium oxygen adduct with 1,3-bis(di-t-butylphosphinomethyl)benzene [RhO2{tBu2PCH2(C6H3)CH2PtBu2}] (5) was also investigated. In this species the O2 is η2 coordinated to the Rh(I) center with asymmetric Rh–O bond lengths (2.087(7) and 1.998(8)Å). The O–O bond distance is short (1.337(11)Å) with νO–O of 990.5cm−1. DFT calculations on complex 5 yielded two η2–O2 structures that differed in energy by only 0.76kcal/mol. The lower energy one (5a) had near C2 symmetry, and had nearly equal Rh–O bond lengths, while the higher energy structure (5b) had near Cs symmetry and generally good agreement with the experimental structure. The calculated UV–Vis and IR spectra of complex 5 are in excellent agreement with experiment.

Magnesium Cyclam complexes with a Mg2(Bn2Cyclam) core: Structural characterization of Mg2(Bn2Cyclam)I2 and Mg2(Bn2Cyclam){μ-H}{μ-F-C6F4}2BC6F5

This work describes the crystal structures of two Mg dimers supported by dianionic trans-disubstituted Bn2Cyclam ligands (1,8-dibenzyl-1,4,8,11-tetraazacyclotetradecane). Mg2(Bn2Cyclam)I2 (1) crystallizes in the monoclinic space group P21/c with half-molecule in the asymmetric unit. The two metal centers and the two Namido donors of the cyclam ring define a four-member Mg2N2 metallacycle. The metals’ coordination spheres are completed by one amine of the macrocycle and one iodide defining a trigonal pyramidal coordination geometry. Mg2(Bn2Cyclam){μ-H}{μ-F-C6F4}2BC6F5 (2) crystallizes in the monoclinic space group P21/c with half-molecule in the asymmetric unit. Compound 2 is a rare example of a zwitterionic species of the type [Mg2(Bn2Cyclam)]2+ with two [HB(C6F5)3]− anions coordinating in a k3-H,F,F tridentate fashion. This compound also displays bridging Namido ligands that bind the two Mg atoms in a Mg2N2 arrangement analogous to 1, promoting a capped square pyramidal coordination geometry. At a supramolecular level C–H⋯I and C–H⋯F hydrogen bonds as well as CH/π and F⋯F interactions are responsible for the crystal packing.

Four-Coordinate, 14-Electron RuII Complexes: Unusual Trigonal Pyramidal Geometry Enforced by Bis(phosphino)silyl Ligation

Unprecedented diamagnetic, four-coordinate, formally 14-electron (Cy-PSiP)RuX (Cy-PSiP = [κ(3)-(2-R(2)PC(6)H(4))(2)SiMe](-); X = amido, alkoxo) complexes that do not require agostic stabilization and that adopt a highly unusual trigonal pyramidal coordination geometry are reported. The tertiary silane [(2-Cy(2)PC(6)H(4))(2)SiMe]H ((Cy-PSiP)H) reacted with 0.5 [(p-cymene)RuCl(2)](2) in the presence of Et(3)N and PCy(3) to afford [(Cy-PSiP)RuCl](2) (1) in 74% yield. Treatment of 1 with KO(t)Bu led to the formation of (Cy-PSiP)RuO(t)Bu (2, 97% yield), which was crystallographically characterized and shown to adopt a trigonal pyramidal coordination geometry in the solid state. Treatment of 1 with NaN(SiMe(3))(2) led to the formation of (Cy-PSiP)RuN(SiMe(3))(2) (3, 70% yield), which was also found to adopt a trigonal pyramidal coordination geometry in the solid state. The related anilido complexes (Cy-PSiP)RuNH(2,6-R(2)C(6)H(3)) (4, R = H; 5, R = Me) were also prepared in >90% yields by treating 1 with LiNH(2,6-R(2)C(6)H(3)) (R = H, Me) reagents. The solid state structure of 5 indicates a monomeric trigonal pyramidal complex that features a C-H agostic interaction. Complexes 2 and 3 were found to react readily with 1 equiv of H(2)O to form the dimeric hydroxo-bridged complex [(Cy-PSiP)RuOH](2) (6, 94% yield), which was crystallographically characterized. Complexes 2 and 3 also reacted with 1 equiv of PhOH to form the new 18-electron η(5)-oxocyclohexadienyl complex (Cy-PSiP)Ru(η(5)-C(6)H(5)O) (7, 84% yield). Both amido and alkoxo (Cy-PSiP)RuX complexes reacted with H(3)B·NHRR' reagents to form bis(σ-B-H) complexes of the type (Cy-PSiP)RuH(η(2):η(2)-H(2)BNRR') (8, R = R' = H; 9, R = R' = Me; 10, R = H, R' = (t)Bu), which illustrates that such four-coordinate (Cy-PSiP)RuX (X = amido, alkoxo) complexes are able to undergo multiple E-H (E = main group element) bond activation steps. Computational methods were used to investigate structurally related PCP, PPP, PNP, and PSiP four-coordinate Ru complexes and confirmed the key role of the strongly σ-donating silyl group of the PSiP ligand set in enforcing the unusual trigonal pyramidal coordination geometry featured in complexes 2-5, thus substantiating a new strategy for the synthesis of low-coordinate Ru species. The mechanism of the activation of ammonia-borane by such low-coordinate (R-PSiP)RuX (X = amido, alkoxo) species was also studied computationally and was determined to proceed most likely in a stepwise fashion via intramolecular deprotonation of ammonia and subsequent borane B-H bond oxidative addition steps.

Hydrothermal synthesis, structure and photoluminescent property of a novel sodium-pyrazinyltetrazole framework compound

Abstract A novel coordination polymer of sodium [Na2(Pzta)2(H2O)2]n (1) has been synthesized hydrothermally by reacting pyrazine carbonitrile and sodium azide in the presence of aluminum(III) chloride as Lewis acid catalyst. Complex 1 was characterized by elemental analysis, thermal gravimetric analysis and IR spectroscopy. Single crystal X-ray diffraction revealed that complex 1 has both distorted trigonal bipyramidal and square pyramidal coordination geometries around sodium atoms. Complex 1 represents the first hydrothermally synthesized 1D sodium monotetrazole coordination polymer. Strong hydrogen bonds are formed between water molecules and nitrogen atoms of both pyrazine and tetrazole rings which result in the formation of a 2D metallosupramolecular network. The luminescence properties of 1 were also investigated at room temperature in the solid state.

Orange and Yellow Crystals of Copper(I) Complexes Bearing 8-(Diphenylphosphino)quinoline: A Pair of Distortion Isomers of an Intrinsic Tetrahedral Complex

The tetrafluoroborate salt of bis{8-(diphenylphosphino)quinoline}copper(I), [Cu(Ph(2)Pqn)(2)]BF(4), afforded orange prismatic (2O) or yellow columnar (2Y) crystals, dependent on the solvent and concentration of the recrystallization solution used. X-ray analysis revealed that crystals of 2O and 2Y had the same composition and exhibited different crystal systems: 2O was triclinic, with space group P ̅1 and Z = 2, and 2Y was monoclinic with space group P2(1)/c and Z = 4. In these crystals, the tetrahedral copper(I) complex exhibited a strong "rocking distortion" toward a trigonal pyramidal coordination geometry (by a slide translation of one of the unsymmetrical bidentate chelating ligands along the tetrahedral edge). In addition, both the 2O and 2Y complexes showed a "flattening distortion", meaning that the dihedral angle between the two chelate planes were off-perpendicular and oriented toward opposite directions, which resulted in a pair of distortion isomers: syn clinal (sc: 2O) and anti clinal (ac: 2Y). (31)P CP-MAS NMR spectroscopy indicated that 2O and 2Y could be distinguished. Both isomers exhibited inequivalent P atoms, but a larger difference in chemical shift was observed in 2Y. TD-DFT calculations reproduced the difference in spectra between the orange- and yellow-colored complexes, which originated from metal-to-ligand charge-transfer transitions.

A Cagelike Polyanion with a Ag+ Enwrapped, [AgAs2Mo15O54]11−

The polyanion [AgAs(2)Mo(15)O(54)](11-) has an unusual cage-like structure composed of [AsMo(6)O(27)](15-) and [AsMo(6)O(24)](9-) subunits connected by three MoO(4) tetrahedra, and a Ag(+) cation is inclosed at the center of the cage and coordinated by two As atoms with a As-Ag-As bond angle of 180° along with three μ(3)-oxo groups from MoO(4) tetrahedra to lead to a trigonal-pyramidal coordination geometry. The compound was also characterized by IR, X-ray photoelectron spectroscopy, fluorescent spectroscopy, and thermogravimetry-differential scanning calorimetry. The stability of [AgAs(2)Mo(15)O(54)](11-) in aqueous solution was investigated by using electronic absorbance spectroscopy and electrospray ionization mass spectrometry.

Synthesis of LithiumN-pentafluorophenyl,N′-trimethylsilyl 2-Pyridylamidinate and Its Cyclization to Lithium Tetrafluoro-2-(2-pyridyl)benzimidazolate via a Me3SiF Elimination. Coordination Chemistry, Reactivity, and Mechanism

When N-trimethylsilylpentafluoro aniline reacts with BuLi in the presence of THF or TMEDA, the corresponding THF (2) or TMEDA (4) lithium anilides are obtained. Complex 4 is monomeric in the solid state, with a distorted trigonal pyramidal coordination geometry at the lithium center. The strong C-F-->Li interaction in this complex is also accompanied by the elongation of the C-F bond. Mild heating of complex 4 with 2-cyanopyridine results in rapid evolution of Me(3)SiF to quantitatively yield the tetrafluoro-2-(2-pyridyl)benzimidazolate lithium complex (6). From the reaction mixture of complex 4 the asymmetric N-trimethylsilyl, N'-pentafluorophenyl-2-pyridylamidinate lithium complex (5) was isolated as a dormant intermediate. Complex 5 possesses several unusual bonding features with the most notably being a very short Si-N bond length and a rare kappa(1)-Z-syn amidinate bonding mode. A mechanism that includes silicon assisted C-F bond activation is proposed for the cyclization reaction based on the structural parameters of complexes 5 and 6, and on (1)H, (19)F, and (13)C NMR studies.

Electrochemical syntheses and structures of lead(II) and bismuth(III) complexes of 4-(trimethylammonio)benzenethiolate

Two main-group metal complexes of the zwitterionic ammonium thiolate complexes, [M(Tab) 3](ClO 4) n (Tab = 4-(trimethylammonio)benzenethiolate) ( 1: M = Pb, n = 2; 2: M = Bi, n = 3), were prepared by electrochemical oxidation of Pb or Bi electrode in MeCN containing Tab and Et 4NClO 4. Each M atom in 1 and 2 is coordinated by three S atoms of three Tab ligands, forming a trigonal pyramidal coordination geometry. The resulting [M(Tab) 3] n+ cations are interconnected by secondary M⋯S interactions to form two different 1D cationic chains. The electrochemical properties of 1 and 2 were also investigated by cyclic voltammetry.

Coordination compounds of N, N′-olefin functionalized imidazolin-2-ylidenes

N-Heterocyclic carbene ligands (NHC) were metalated with Pd(OAc) 2 or [Ni(CH 3CN) 6](BF 4) 2 by in situ deprotonation of imidazolium salts to give the N-olefin functionalized biscarbene complexes [MX 2(NHC) 2] 3– 7 ( 3: M = Pd, X = Br, NHC = 1,3-di(3-butenyl)imidazolin-2-ylidene; 4: M = Pd, X = Br, NHC = 1,3-di(4-pentenyl)imidazolin-2-ylidene; 5: M = Pd, X = I, NHC = 1,3-diallylimidazolin-2-ylidene; 6: M = Ni, X = I, NHC = 1,3-diallylimidazolin-2-ylidene; 7: M = Ni, X = I, NHC = 1-methyl-3-allylimidazolin-2-ylidene). Molecular structure determinations for 4– 7 revealed that square-planar complexes with cis ( 5) or trans ( 4, 6, 7) coordination geometry at the metal center had been obtained. Reaction of nickelocene with imidazolium bromides afforded the η 5-cyclopentadienyl (η 5-Cp) monocarbene nickel complexes [NiBr(η 5-Cp)(NHC)] 8 and 9 ( 8: NHC = 1-methyl-3-allylimidazolin-2-ylidene; 9: NHC = 1,3-diallylimidazolin-2-ylidene). The bromine abstraction in complexes 8 and 9 with silver tetrafluoroborate gave complexes [NiBr(η 5-Cp)(η 3-NHC)] 10 and 11. The X-ray structure analysis of 10 and 11 showed a trigonal-pyramidal coordination geometry at the nickel(II) center and coordination of one N-allyl substituent.

Quantitative geometric descriptions of the belt iron atoms of the iron-molybdenum cofactor of nitrogenase and synthetic iron(II) model complexes.

Six of the seven iron atoms in the iron-molybdenum cofactor of nitrogenase display an unusual geometry, which is distorted from the tetrahedral geometry that is most common in iron-sulfur clusters. This distortion pulls the iron along one C3 axis of the tetrahedron toward a trigonal pyramid. The trigonal pyramidal coordination geometry is rare in four-coordinate transition metal complexes. In order to document this geometry in a systematic fashion in iron(II) chemistry, we have synthesized a range of four-coordinate iron(II) complexes that vary from tetrahedral to trigonal pyramidal. Continuous shape measures are used for a quantitative comparison of the stereochemistry of the Fe atoms in the iron-molybdenum cofactor with those of the presently and previously reported model complexes, as well as with those in polynuclear iron-sulfur compounds. This understanding of the iron coordination geometry is expected to assist in the design of synthetic analogues for intermediates in the nitrogenase catalytic cycle.

A tetrameric copper(I) alkoxide with a π-tethered ligand: 2-allyl-6-methylphenoxocopper(I)

The complex 2-allyl-6-methylphenoxocopper(I) has been prepared by reaction between mesitylcopper(I) and 2-allyl-6-methylphenol. Crystallographic studies show that the compound is tetrameric with a distorted cubane-type copper(I)-oxygen core, and with additional π-coordination of the ligand to copper through the alkene functionality ( ν(CC)=1520 cm −1). The ligands thus act both as chelates and as bridges between adjacent copper(I) centres. Copper(I) exhibits trigonal pyramidal coordination geometry with CuC distances to the CC group of 1.976(9) and 2.017(11) Å and CuO distances of 1.973(6), 2.021(6) and 2.577(6) Å, respectively.

Structure of the M148Q mutant of rusticyanin at 1.5 Å: a model for the copper site of stellacyanin

The small blue copper protein rusticyanin from Thiobacillus ferrooxidans contains a type 1 Cu centre with a single axial ligand, Met148, which together with the His-Cys-His trigonal planar ligands produces a distorted trigonal pyramidal coordination geometry to copper. Type 1 Cu sites are found in cupredoxins and several multicopper proteins, including oxidases and nitrite reductases. The role of the axial ligand has been extensively debated in terms of its function in the fine tuning of the redox potential and spectroscopic properties of type 1 Cu sites. Numerous mutations of the Met ligand in azurins have been studied, but interpretation of the results has been complicated by the presence of the additional carbonyl oxygen ligand from Gly45, a neighbouring residue to the coordinating His46. The importance of the axial ligand has been further emphasized by the finding that the type 1 centre in Rhus vernicifera stellacyanin, with the lowest redox potential in a type 1 Cu site of 184 mV, has Gln as the axial ligand, whilst fungal laccase and ceruloplasmin, which have redox potentials of 550-800 mV, have a Leu in this position. Here, the crystal structure of the M148Q mutant of rusticyanin at 1.5 A resolution is presented. This is a significantly higher resolution than that of the structures of native rusticyanin. In addition, the M148Q structure is that of the oxidized protein while the native structures to date are of the reduced protein. The mutant protein crystallizes with two molecules per asymmetric unit, in contrast to the one present in the native crystal form. This mutant's redox potential (550 mV at pH 3.2) is lowered compared with that of the native protein ( approximately 670 mV at pH 3.2) by about 120 mV. The type 1 Cu site of M148Q closely mimics the structural characteristics of the equivalent site in non-glycosylated cucumber stellacyanin (redox potential approximately 260 mV) and, owing to the absence in rusticyanin of the fifth, carbonyl ligand present in azurin, may provide a better model for the R. vernicifera stellacyanin (redox potential approximately 184 mV) type 1 Cu site, which also lacks the fifth ligand. Furthermore, the presence of two molecules in the asymmetric unit cell indicates a potential binding region of the redox partners.