Equatorial Donor Atoms Research Articles

Multinuclear Co(II) and Zn(II) salamo-based complexes with unique τ5 parameters: Structure characterizations, Hirshfeld surfaces and fluorescence properties

The multinuclear Co(II) and Zn(II) salamo-based complexes [{Co2(L)(μ-OMe)}8]·11CH3OH·2H2O (1) and [Zn2(L)(μ-OEt)]·CHCl3 (2) have been successfully isolated by the solvent evaporation method and characterized structurally by elemental analyses, IR spectra and UV–Vis spectra. Complex 1 consists of four closely related neutral dinuclear units, 1A, 1B, 1C and 1D, while complex 2 consists of three closely related neutral dinuclear units 2A, 2B and 2C. Complexes 1 and 2 are unique examples of crystallographically independent but chemically identical molecules with unique τ5 parameters. For complex 1, all the Co(II) atoms possess extremely distorted trigonal bipyramidal geometries, except the for Co4 atom, with the Co(II) atoms lying out of the plane of the equatorial donor atoms. For complex 2, except for the Zn5 atom, the Zn(II) atoms possess extremely distorted trigonal bipyramidal geometries and square-based pyramidal geometries. Significantly, the geometries about the Co4 and Zn5 atoms show τ5 values very close to 0.500 and there are few such examples like those. Complex 2 has an obvious fluorescence enhancement, which may be caused by intramolecular charge transfer (ICT) and blocks the ligand to the metal charge transfer transition (LMCT) process. The intermolecular interactions were quantitatively analyzed by Hirshfeld surface analyses.

Insight into D6h Symmetry: Targeting Strong Axiality in Stable Dysprosium(III) Hexagonal Bipyramidal Single-Ion Magnets.

Following a novel synthetic strategy where the strong uniaxial ligand field generated by the Ph3SiO− (Ph3SiO−=anion of triphenylsilanol) and the 2,4‐di‐tBu‐PhO− (2,4‐di‐tBu‐PhO−=anion of 2,4‐di‐tertbutylphenol) ligands combined with the weak equatorial field of the ligand LN6, leads to [DyIII(LN6)(2,4‐di‐tBu‐PhO)2](PF6) (1), [DyIII(LN6)(Ph3SiO)2](PF6) (2) and [DyIII(LN6)(Ph3SiO)2](BPh4) (3) hexagonal bipyramidal dysprosium(III) single‐molecule magnets (SMMs) with high anisotropy barriers of U eff=973 K for 1, U eff=1080 K for 2 and U eff=1124 K for 3 under zero applied dc field. Ab initio calculations predict that the dominant magnetization reversal barrier of these complexes expands up to the 3rd Kramers doublet, thus revealing for the first time the exceptional uniaxial magnetic anisotropy that even the six equatorial donor atoms fail to negate, opening up the possibility to other higher‐order symmetry SMMs.

Insight into D6h Symmetry: Targeting Strong Axiality in Stable Dysprosium(III) Hexagonal Bipyramidal Single‐Ion Magnets

AbstractFollowing a novel synthetic strategy where the strong uniaxial ligand field generated by the Ph3SiO− (Ph3SiO−=anion of triphenylsilanol) and the 2,4‐di‐tBu‐PhO− (2,4‐di‐tBu‐PhO−=anion of 2,4‐di‐tertbutylphenol) ligands combined with the weak equatorial field of the ligand LN6, leads to [DyIII(LN6)(2,4‐di‐tBu‐PhO)2](PF6) (1), [DyIII(LN6)(Ph3SiO)2](PF6) (2) and [DyIII(LN6)(Ph3SiO)2](BPh4) (3) hexagonal bipyramidal dysprosium(III) single‐molecule magnets (SMMs) with high anisotropy barriers of Ueff=973 K for 1, Ueff=1080 K for 2 and Ueff=1124 K for 3 under zero applied dc field. Ab initio calculations predict that the dominant magnetization reversal barrier of these complexes expands up to the 3rd Kramers doublet, thus revealing for the first time the exceptional uniaxial magnetic anisotropy that even the six equatorial donor atoms fail to negate, opening up the possibility to other higher‐order symmetry SMMs.

Single-Molecule Magnet Properties of Transition-Metal Ions Encapsulated in Lacunary Polyoxometalates: A Theoretical Study.

Single-molecule magnet (SMM) properties of transition-metal complexes coordinated to lacunary polyoxometalates (POM) are studied by means of state of the art ab initio methodology. Three [M(γ-SiW10O36)2] (M = Mn(III), Fe(III), Co(II)) complexes synthesized by Sato et al. (Chem. Commun. 2015, 51, 4081-4084) are analyzed in detail. SMM properties for the Co(II) and Mn(III) systems can be rationalized due to the presence of low-energy excitations in the case of Co(II), which are much higher in energy in the case of Mn(III). The magnetic behavior of both cases is consistent with simple d-orbital splitting considerations. The case of the Fe(III) complex is special, as it presents a sizable demagnetization barrier for a high-spin d(5) configuration, which should be magnetically isotropic. We conclude that a plausible explanation for this behavior is related to the presence of low-lying quartet and doublet states from the iron(III) center. This scenario is supported by ab initio ligand field analysis based on complete active space self-consistent field results, which picture a d-orbital splitting that resembles more a square-planar geometry than an octahedral one, stabilizing lower multiplicity states. This coordination environment is sustained by the rigidity of the POM ligand, which imposes a longer axial bond distance to the inner oxygen atom in comparison to the more external, equatorial donor atoms.

Synthesis, Crystal Structure, and Antimicrobial Activity of Manganese(III) and Iron(III) Complexes Derived from Similar bis-Schiff Bases

A new manganese(III) complex, [Mn(L1)(CH3OH)(dca)] 1, and a new iron(III) complex, [Fe(L2)(CH3OH)(NCS)] 2, for which dca is dicyanoamide anion, and L1 and L2 are the dianionic form of N,N′-3,4-methylphenylenebis(5-methylsalicylaldimine) and N,N′-bis(5-methylsalicylidene)-o-phenylenediamine, respectively, have been prepared and characterized by elemental analyses, IR, and single-crystal X-ray crystallographic determination. The crystal of complex 1 is orthorhombic: space group Pna21, a = 14.6557(6), b = 10.8906(5), c = 15.0536(7) Å, V = 2402.7(2) Å3, Z = 4, R1 = 0.0321, wR2 = 0.0715. The crystal of complex 2 is monoclinic: space group C2/c, a = 14.6798(9), b = 11.1306(7), c = 27.831(1) Å, β = 93.782(2)°, V = 4537.6(5) Å3, Z = 8, R1 = 0.0423, wR2 = 0.1027. The bis-Schiff base ligands coordinate to the metal center through phenolate O and imine N atoms. Both the Mn and Fe atoms in the complexes are in octahedral coordination, with the equatorial donor atoms come from the Schiff base ligands, and with the axial donor atoms come from a methanol O atom and a pseudohalide N atom. The effects of the complexes on the antimicrobial activity against Staphylococcus aureus, Escherichia coli, and Candida albicans were studied.

Synthesis, crystal structure and antimicrobial activity of a hetero trinuclear manganese(III)-iron(II) complex derived from N,N’-bis(5-methylsalicylidene)-1,2-diaminoethane

A new hetero trinuclear manganese(III)-iron(II) complex, [Mn(salen)(H2O)]2[Fe(CN)6], in which salen is the dianionic form of N,N’-bis(5-methylsalicylidene)-1,2-diaminoethane, has been prepared and characterized by elemental analyses, IR, and single crystal X-ray crystallographic determination. The crystal of the complex is monoclinic: space group P21/c, a = 10.768(2), b = 14.248(3), c = 15.222(3) Å, β = 95.394(2)º, V = 2325.0(8) Å3, Z = 2, R1 = 0.0754, wR2 = 0.2366. The bis-Schiff base ligand coordinates to the Mn atom through phenolate O and imine N atoms. Each Mn atom in the complex is in octahedral coordination, with the equatorial donor atoms come from the Schiff base ligand, and with the axial donor atoms come from a water O atom and a cyanide N atom. The effects of the complex on the antimicrobial activity against Staphylococcus aureus, Escherichia coli, and Candida albicans were studied. KEY WORDS: Schiff base, Manganese(III) complex, Iron(II) complex, Heteronuclear, Crystal structure Bull. Chem. Soc. Ethiop. 2015, 29(3), 407-413.DOI: http://dx.doi.org/10.4314/bcse.v29i3.8

A hetero trinuclear manganese(III)-iron(II) complex derived from N,N′-bis(5-chlorosalicylidene)-1,2-diaminoethane: Synthesis, crystal structure, and antimicrobial activity

A new hetero trinuclear manganese(III)-iron(II) complex, [Mn(ClSalen)(H2O)]2[Fe(CN)5(NO)] · CH3OH · H2O, where ClSalen is the dianionic form of N,N′-bis(5-chlorosalicylidene)-1,2-diaminoethane, has been prepared and characterized by elemental analyses, IR, and single crystal X-ray crystallographic determination (CIF file CCDC no. 1024666). The crystal of the complex is orthorhombic: space group Pca21, a = 27.784(2), b = 10.8876(6), c = 15.1755(8) A, V = 4590.5(4) A3, Z = 2, R1 = 0.0596, wR2 = 0.1406. The bis-Schiff base ligand coordinates to the Mn atom through two phenolate O and two imine N atoms. Each Mn atom in the complex is in octahedral coordination, with the equatorial donor atoms come from the Schiff base ligand, and with the axial donor atoms come from a water O atom and a cyanide N atom. The effects of the complex on the antimicrobial activity against Staphylococcus aureus, Escherichia coli, and Candida albicans were studied.

Oxidovanadium(IV) Schiff Base Complex Derived from Vitamin B6: Synthesis, Characterization, and Insulin Enhancing Properties

A new Schiff base, [H(4)pydmedpt](2+)·2Cl(-), derived from one of the forms of vitamin B(6) has been synthesized by condensation of pyridoxal hydrochloride with N,N-bis[3-aminopropyl]-methylamine (medpt) and characterized by analytical and spectroscopic methods. The molecular structure is calculated by density functional theory (DFT) procedures, and the donor properties of each individual donor atom are evaluated by calculation of the Fukui function. One pot reaction of pyridoxal and medpt with vanadyl acetylacetonate yields the brown complex [V(IV)O(H(2)pydmedpt)](2+)·2Cl(-)1, which upon recrystallization from water crystallizes as [V(IV)O(pydmedpt)]·5H(2)O 2. The compounds are characterized by analytical and spectroscopic methods, 2 being also characterized by single crystal X-ray diffraction. It displays a slightly distorted octahedral geometry around the vanadium atom involving the coordination of N(amine), two N(imine), and O(phenolato) donors of the ligand. One of the phenolato oxygen donors is positioned trans to the terminal O-oxido atom with relatively short V-O(phenolate) {2.041(3) Å} and long V-O(oxido) {1.625(4) Å} bond distances when compared to other known compounds. The two different pK(a) values (6.0 and 7.9) obtained for 1 are due to protonation of the pyridine ring nitrogen atoms having different basic characters, this being also substantiated by theoretical calculation of the proton affinity of the O- and N- atoms of the molecule. The spin Hamiltonian parameters are obtained from the electron paramagnetic resonance (EPR) spectra, but the A(z) value (ca. 155 × 10(-4) cm(-1)) is lower than expected by applying the additivity rule for the present set of equatorial donor atoms (ca. 162-163 × 10(-4) cm(-1)), this being attributed to the strong trans V-O(phenolate) bond. The UV-vis transitions and EPR spectral parameters are calculated by DFT procedures, and both the calculated electronic transitions and the hyperfine coupling constants agree well with those experimentally observed. The inhibitory effect of 1 on FFA release and % glucose uptake determined with isolated rat adipocyte cells gave IC(50) and EC(50) values lower than for V(IV)OSO(4) and of the same order of magnitude of other reported insulin enhancing vanadium compounds.

Synthesis and structural characterization of isomeric ‘lantern-shaped’ platinum(III) complexes of formula [Pt 2(PPh 3)X{ N(H)C(R) O} 4](NO 3) 2 (X=PPh 3, H 2O)

The platinum(III) lantern type complexes [Pt 2(PPh 3) 2{ N(H)C(R) O} 4](NO 3) 2 [R=Me ( 1), Bu t ( 2)], and [Pt 2(H 2O)(PPh 3){ N(H)C(Bu t) O} 4](NO 3) 2 ( 3) were synthesized and characterized by 1H NMR and X-ray crystallography ( 2 and 3). The compounds can give rise to formation of isomers differing for the sets of equatorial donor atoms around each platinum, N 3O/NO 3 or N 2O 2, and, in the case of N 2O 2, for the cis or trans geometry. The effect of the anion upon the chemical shifts of NH protons was studied for NO 3 − , BF 4 − , and ClO 4 − . The stability of phosphine axial ligands in the complexes N 3O/NO 3–[Pt 2(PPh 3) 2{ N(H)C(R) O} 4](NO 3) 2 as a function of the set of donor atoms was also studied. The complex N 3O/NO 3– 3 is the fist non-symmetric lantern-type platinum dimer to be characterized by X-ray diffraction. Comparison of the platinum/axial ligand bond distances in different complexes of this type allows to conclude that two factors contribute to the lengthening of axial bonds: the strong trans labilizing effect of the intermetallic bond and the trans-influence of the axial ligand on the second platinum unit.

Monomeric, trimeric and polymeric assemblies of dicopper(ii) complexes of a triazolate-containing Schiff-base macrocycle

The new triazolate-containing Schiff-base macrocyclic ligand L22− has been synthesised as [PbII2(L2)](ClO4)2, 1, by the [2 + 2] cyclisation reaction of 3,5-diacetyl-1H-1,2,4-triazole and 1,3-diaminopropane using lead(II) template ions. The macrocycle provides four nitrogen atoms, two imine and two triazolate donors, as equatorial donor atoms to each of the two metal ions in the macrocycle. A series of copper(II) complexes of the L22− macrocycle has been produced with a variety of axial donors. Each copper complex has been structurally characterised by X-ray diffraction and three different structural types can be distinguished: monomeric, trimeric and polymeric. These different types arise from adding a different ratio of thiocyanate ions to the copper(II) transmetallation reaction of [PbII2(L2)](ClO4)2 (1). The monomeric dicopper(II) macrocyclic complexes include [CuII2(L2)(NCMe)2](ClO4)2 (2) and [CuII2(L2)(NCS)2] (3). The trimeric complex {[CuII2(L2)]3(NCS)2}(ClO4)4 (4) consists of three dicopper(II) macrocyclic complexes bridged by two thiocyanate ions. The thiocyanate-bridged polymeric complex {[CuII2(L2)(NCS)][CuII2(L2)(SCN)](ClO4)2}x (5) comprises two types of macrocyclic units in the repeating unit. A second polymeric isomer {[CuII2(L2)(NCS)](ClO4)}x (6), incorporating a more symmetrical thiocyanate-bridging mode that has only one type of macrocyclic unit in the repeating unit, is also reported.

Model investigations for vanadium-protein interactions: vanadium(III) compounds with dipeptides and their oxovanadium(IV) analogues

The reaction of VCl(3) with 1,10-phenanthroline and a series of dipeptides (H(2)dip), having aliphatic as well as aromatic side chains, in methyl alcohol and in the presence of triethylamine affords vanadium(III) compounds of the general formula [V(III)(dip)(MeOH)(phen)]Cl. Aerial oxidation/hydrolysis of the vanadium(III) species gives their oxovanadium(IV) analogues of the general formula [V(IV)O(dip)(phen)]. X-ray crystallographic characterization of the [V(IV)O(dip)(phen)] compounds (where dip(2-)=Gly- L-Ala, Gly- L-Val and Gly- L-Phe) revealed that the vanadium atom possesses a severely distorted octahedral coordination and is ligated to a tridentate dip(2-) ligand at the N(amine) atom, the deprotonated N(peptide) atom and one of the O(carboxylate) atoms, as well as an oxo group and two phenanthroline nitrogen atoms. Circular dichroism characterization of the V(III)/V(IV)O(2+)-dipeptide compounds revealed a strong signal for the V(IV)O(2+) species in the visible range of the spectrum, with a characteristic pattern which may be exploited to identify the N(am), N(pep) and O(car) ligation of a peptide or a protein to V(IV)O(2+) center, and a weak Cotton effect of opposite sign to their vanadium(III) analogues. The visible spectra of the V(III)-dipeptide compounds revealed two d-d bands with high intensity, thus indicating that the covalency of the metal-donor atoms is significant, i.e. the vanadium d orbitals are significantly mixed with the ligand orbitals, and this is confirmed by the low values of their Racah B parameters. The high-intensity band of the V(IV)O(2+)-dipeptide compounds at approximately 460 nm implies also a strong covalency of the metal with the equatorial donor atoms and this was supported by the EPR spectra of these compounds. Moreover, the V(III)/V(IV)O(2+)-dipeptide complexes were characterized by EPR and IR spectroscopies as well as conductivity and magnetic susceptibility measurements.

Antitumour copper(II) salicylaldehyde benzoylhydrazone (H 2sb) complexes: physicochemical properties and the single-crystal X-ray structures of [{Cu(H 2sb)(CCl 3CO 2) 2} 2] and [{Cu(Hsb) (ClO 4) (C 2H 5OH)} 2] and the related salicylaldehyde acetylhydrazone (H 2sa) complex, [Cu(Hsa)Cl(H 2O)]·h 2O

Copper(II) complexes of the antitumour ligand salicylaldehyde benzoylhydrazone (H 2sb) have been prepared. In the presence of strong acids, complexes of the neutral ligand were isolated: [{Cu(H 2sb)X 2} 2]· nH 2O (X = Br, n X = CCl 3CO 2, n = 0) and [Cu(H 2sb)Cl 2(H 2O)]. In weakly acid or neutral media, monoanionic compounds separated: Cu(HsB)X 2· nH 2O] (X = Cl,Br, NO 3, 0.3SO 4, n = 0; X = ClO 4, n = 1). With base only the highly insoluble dianionic complex [{Cu(sb)} 2] was isolated. Also prepared was the related anionic ligand complex [Cu(Hsa)Cl(H 2O)]·H 2O (H 2sa = salicylaldehyde acetylhydrazone). The complexes have been characterised by a range of physicochemical techniques and the crystal and molecular structures of [{Cu(H 2sb)(CCl 3CO 2) 2} 2], [{Cu(Hsb)ClO 4(C 2H 5OH)} 2] and [Cu(Hsa)Cl(H 2O)]·H 2O, determined by single-crystal X-ray diffraction studies. Crystals [{Cu(H 2sb)(CCl 3CO 2) 2} 2] are triclinic, space group P 1 , with = 10.130(2), b = 11.660(2), c = 11.876(2)r α = 67.07(2), β = 109-09(2) γ = 107.84(2)° and Z = 2. The complex is a centrosymmetric dimer, the monomeric units being bridged through the phenol oxygen. The copper coordination is tetragonal with the equatorial donor atoms coming from the tridentate ‘ONO’ donor ligand and the symmetry-related phenol oxygen. The more weakly bound axial donor oxygens are from the coordinated trichloroacetates. Crystals of [Cu(Hsb)ClO 4(C 2H 5OH) 2] are monoclinic, space group P2 1/ c, with a = 11.2281(8), b = 7.9129(4), c = 21.043(1) ;rA β = 98.560(6)°✓ and Z = 4. This complex is also a centrosymmetric dimer, the monomeric units being bridged through the phenoxy oxygen. The copper coordination is tetragonal with the equatorial donor atoms coming from the tridentate ‘ONO’ ligand and the symmetry related phenoxy oxygen. The more weakly bound axial donor oxygens are supplied by the ethanol and perchlorato moieties. Crystals of [Cu(Hsa)Cl(H 2O)]·H 2O are monoclinic, space group P2 1/ c, with a = 7.4877(4), b = 15.5806(7), c = 10.5208(3) A ̊ , β = 103.56(4)° and Z = 4 . The complex is monomeric with the copper(II) adopting a square-pyramidal coordination. The four in-plane donors are provided by the tridentate ‘ONO’ donor Hsa and an oxygen from a coordinated water molecule; the axial site is occupied by the chloride ion. Most of the complexes have low magnetic moments and are assigned dimeric side-by-side structures. Powder ESR spectra have g 1 and g ✓ resolved often with ΔM = 2 transitions present.

Copper(II) complexes of the antitumour-related ligand salicylaldehyde acetylhydrazone (H 2L) and the single-crystal X-ray structures of [{Cu(HL)H 2O} 2] · 2(NO 3) and [{Cu(HL) (pyridine) (NO 3)} 2

Binary and ternary copper(II) complexes of the ligand salicylaldehyde acetylhydrazone (H 2L) have been prepared. In acid or neutral media monoanionic HL complexes separate. Addition of the Lewis bases pyridine (py) and thiourea (tu) to [{Cu(HL)H 2O} 2] · 2(NO 3) results in the monoanionic ternary ligand adducts [{Cu(HL) (py) (NO 3)} 2] and [Cu(HL) (tu) (NO 3)], respectively. With base, the le soluble dianionic complex [{CuL} 2] was isolated. Addition of py to [{CuL} 2]afforded the dianionic ternary complex [ CuL(py)]· 1 2 H 2 O . The complexes have been characterized by a range of physicochemical techniques and the crystal and molecular structures of [{Cu(HL)H 2O} 2] · 2(NO 3) and [{Cu(HL) (py) (NO 3)} 2] determined. Crystals of [{Cu(HL)H 2O} 2] · 2 (NO 3), C 18H 22Cu 2N 6O 12, are monoclinic, with space group P2 1/c, a=7.217(4), b=11.758(8), c=13.764(8) A ̊ , β=95.47(4)° and Z=4 . [{Cu(HL)H 2O} 2] · 2 (NO 3) is a centrosymmetric (planar) dimer, the monomeric units being bridged through the phenoxy oxygen. The copper atom has a square-pyramidal geometry with the basal donor atoms coming from the tridentate ligand (ONO) and the symmetry-related phenolate (O). The more weakly bound apical donor oxygen is supplied by a coordinated water molecule. The nitrate is not bound. Crystals of [{Cu(HL)(py) (NO 3)} 2], C 28H 28Cu 2N 8O 10, are monoclinic, with space group P2 1/c, a=10.642(3), b=11.796(3), c=13.137(2) A ̊ , β=111.03(2)° and Z=4. [{Cu(HL) (py) (NO 3)} 2] is a weakly interacting centrosymmetric (stacked) dimer, the monomeric units being bridged axially through the phenoxy oxygen. The copper atom has a tetragonal geometry with the equatorial donor atoms coming from the tridentate ligand (ONO) and the pyridine (N). The more weakly bound nitrato anion provides the other axial donor (O). Several of the complexes exhibit interesting magnetic properties.

EPR characterisation of the CrV intermediates in the CrVI/V oxidations of organic substrates and of relevance to Cr-induced cancers

An empirical method has been developed for determining the coordination number of CrV complexes (five- or six-coordinate) and the donor groups bound to CrV from the measured giso and Aiso values. The giso values depend only on the nature of the donor groups and the number of each group, which is very useful in the characterisation of the coordination number and donors. By contrast, the Aiso values appear to be sensitive to the nature of the equatorial donor atoms and the coordination geometry. Strong correlations have been found between the giso values of isoelectronic CrV and VIV complexes and between the Aiso values of analogous complexes of these two metal ions. These, combined, have been used to understand the solution chemistry of CrV using EPR spectroscopy. Such studies have also been invaluable in unravelling the biochemistry that occurs in cell media and cells exposed to carcinogenic CrVI and, hence, possible mechanisms of Cr-induced cancers.

Polysulfonylamine: XXVII. Synthese von Dimethylindium-und Bis(trimethylsilylmethyl)indium-dimesylamid sowie Röntgenstrukturanalyse von [(Me 3SiCH 2) 2InN(SO 2Me) 2] 2

The compounds R 2InN(SO 2Me) 2 [R = Me ( 1), Me 3SiCH 2 ( 2)] have been prepared by acidolysis of R 3In with (MeSO 2) 2NH. 2 crystallizes in the monoclinic space group P2 1 with a = 1857.9(8), b = 1207.2(5), c = 1954.8(8) pm, β = 108.60(3)°, U = 4.155 nm 3, Z = 8 monomers. The asymmetric unit contains two crystallographically independent dimers, in which the indium atoms are linked by two N-S-O bridges originating from two (MeSO 2) 2N − ligands to form an eight-membered [InNSO] 2 ring (In-N 232-235, In-O 230-239 pm, C-In-C 136-150°). Additionally, the two MeSO 2 groups exocyclic to the eight-membered ring are weakly linked to the indium atoms in four-membered [InNSO] chelate rings (In⋯O 253–261 pm). The indium atoms are thus five coordinate with very distorted (because of the four-membered rings) trigonal bipyramidal stereochemistry (O-In⋯O 141–146°, N-In⋯O ca. 58°), and are 6.3-25.8 pm out of the NC 2 planes formed by the equatorial donor atoms.