Haloalkyl complexes of the transition metals: IV. The formation of a cationic ylide complex of platinum(II) from a chloromethylplatinum(II) complex and the crystal structures of cis-[Pt(CH2PPh3)X(PPh3)2]I (X = Cl or I)

The reactions of Pt(PPH₃)₄ and Pt(C₂H₄)(PPh₃)₂ with CH₂ClI have been investigated. The product of the reaction of Pt(PPh₃)₄ with CH₂ClI is the cationic ylide complex cis-[Pt(CH₂PPh₃)Cl(PPh₃)2][I], whereas the reaction of Pt(C₂H₄)-(PPh₃)₂ gives the oxidative addition product Pt(CH₂Cl)I(PPh₃)₂. Reaction of cis- or trans-Pt(CH₂Cl)I(PPh₃)₂] with PPh₃ gives the complex cis-[Pt(CH₂PPh₃)-Cl(PPh₃)₂][I]. The structures of the complexes cis-[Pt(CH₂PPh₃X(PPh₃)₂][I] (where X = Cl or I) have been determined by X-ray crystallography. Both complexes crystalize in the monoclinic space group P2₁/n. For X = Cl a 1388.6(7), b 2026.7(10), c 1823.9(9) pm, β 96.51(2)° and R converged to 0.075 for 3542 observed reflections; structural parameters Pt-Cl 240(1), Pt-C(3) 212(2), Pt-P(2) (trans to Cl) 235(1) and Pt-P(1) (trans to CH₂PPh₃) 233(1) pm; Cl-Pt-C(3) 86.9(5), C(3)-Pt-P(2) 91.8(5), P(2)-Pt-P(1) 97.0(2) and P(1)-Pt-Cl 85.1(2)°. For X = I, a 1379.4(7), b 2044.4(10), c 1840.0(9) pm, β 96.09(2)° and R converged to 0.071 for 4333 observed reflections; structural parameters Pt-I 266(1), Pt-C(3) 212(2), Pt-P(2) (trans to I) 226(1) and Pt-P(1) (trans to CH₂PPh₃ 233(1) pm; I-Pt-C(3) 87.2(5), C(3)-Pt-P(2) 91.5(5), P(2)-Pt-P(1) 96.5(2) and P(1)-Pt-I 85.6(1)°. Some other complexes of the type cis-[Pt(CH₂PPh₃)X(PPh₃)₂]Y are also described.     

Nature of the hydrogen bridge in transition metal complexes: I. Molecular orbital calculations of binuclear carbonyls of Cr,Mo Fe and Ni with single hydrogen bridges

Determination of the electronic structure was performed by the parameter-free Fenske-Hall method for the complexes [(CO)₅MHM(CO)₅]⁻ with D_4h, C_2v and C₂ symmetries (wehre M = Cr, Mo) as well as for the complex [(CO)₃NiHNi(CO)₃]⁻ with C_2v and D_3h symmetries and for the complex [(CO)₄FeHFe(CO)₄]⁺ with a D_3h symmetry.The character and stability of the metalhydrogenmetal bridge bond in each of these complexes was compared. The effect of lowering the symmetry on the electronic structure of these complexes is also discussed. The influence of the bridging hydrogen atom on terminal ligands, i.e. its cis effect, was characterized.     

Rotational spectrum of BiBr

The microwave absorption spectra of Bi⁷⁹Br and Bi⁸¹Br have been measured in the 65–100 GHz region. Frequencies of rotational transitions (υ,J + 1) ← (υ,J) in the 0⁺ electronic ground state with J = 26,27 and 35–39, and in the vibrational state υ = 0–11 can be fitted to the expression: ν = 2[Y₀₁ + Y₁₁(υ + $\text{1}\text{2}$) + Y₂₁(υ + $\text{1}\text{2}$)²] (J + 1) + 4Y₀₂(J + 1)³. The results for the Dunham coefficients are: Y₀₁ = 1295.5609(12) MHz, Y₁₁ = ?3.97809(18) MHz, Y₂₁ = 2.303(18) kHz, Y₀₂ = ?220.26(45) Hz for Bi⁷⁹Br, and: Y₀₁ = 1272.3406(12) MHz, Y₁₁ = ?3.87164(16) MHz, Y₂₁ = 2.225(14) kHz, Y₀₂ = ?212.31(45) Hz for Bi⁸¹Br. From these results we have deduced the value for the equilibrium distance r_e, for the potential constants a₀ and a₁, and for the vibrational constants ω_e and ω_eχ_e. The molecular constants of BiBr are almost the same as of TIBr, the situation found also for BiI and TII.     

Evolution of (GaAl) n Clusters and Chemisorptions of H2 on (GaAl) n Clusters

The growth behavior of (GaAl) _n (n = 1–12) and the chemisorptions of hydrogen on the ground state geometries have been studied with the three-parameter hybrid generalized gradient approximation due to Becke-Lee–Yang–Parr (B3LYP). The dissociation energy, the second-order energy differences, and the HOMO–LUMO gaps indicate that the magic numbers of the calculated (GaAl) _n clusters are n = 4 and 6. To my knowledge, this is the first time that a systematic study of chemisorptions of hydrogen on gallium aluminum clusters. The onefold top site of aluminum atom is identified to be the most favorable chemisorptions site for one hydrogen chemisorptions on most (GaAl) _n clusters. In general, dissociative chemisorptions of a hydrogen molecule on a top site of aluminum atom is found common for all sizes clusters considered here except for (GaAl) _n (n = 1–3) clusters. The stability of the (GaAl) _n H _m complexes shows that both large second-order difference and large fragmentation energies for (GaAl)₁₀H₂ and (GaAl)₁₁H₂ make these species behaving like magic clusters.     

Symmetry of Kekulé structures

The symmetry of Kekulé structures for aromatic hydrocarbons is studied by group theory. The general problem of deducing the distribution over irreducible representations (Λ_Kek) or characters of the representation based on the Kekulé structures (χ_Kek) has not been solved. A partial solution is given for two classes of molecules, namely (a) the “straight chain” aromatics (polyacenes): naphthalene, anthracene, naphthacene, etc., and (b) the “zig-zag chain” aromatics: phenanthrene, chrysene, picene, etc. As a part of this solution the number of Kekulé structures (K) in the two cases was found to be (a) K = Q + 1 and (b) K = F_Q+1, respectively. Here Q is the number of benzene rings in the molecule in question, and F_i denotes the i-th member of the Fibonacci series. Symmetrical structures (Λ_Kek) or characters (χ_Kek) are given for a number of additional molecules as examples: benzene (D_6h), tetraphene (C_s), benzo[c] phenanthrene (C_2v), pyrene (D_2h), triphenylene (D_3h), perylene (D_2h), pentaphene (C_2v), dibenzophenanthrene (C_2v), heptaphene (C_2v) and coronene (D_6h). Here the appropriate symmetry groups are given in parentheses.     

Radical copolymerization of N-isopropylacrylamide with anhydrides of maleic and citraconic acids

Radical-initiated copolymerization of N-isopropylacrylamide (NIPA) with maleic (MA) and citraconic (CA) anhydrides was carried out in the presence of 2,2^′-azobisisobutyronitrile (AIBN) as an initiator in 1,4-dioxane at 65 °C under nitrogen atmosphere. Structure and monomer unit compositon of the copolymers obtained from a wide range of monomer feed were determined by elemental analysis (content of N for NIPA units), Fourier transform infrared and ¹H NMR spectroscopy. Monomer reactivity ratios for NIPA (M₁)-MA (M₂) and NIPA (M₁)-CA (M₂) pairs were determined by Kelen-Tüdõs (KT) and non-linear regression (NLR) methods using elemental and ¹H NMR spectroscopy analyses data. They are r₁=0.45 and r₂=0.08 (KT, N analysis), r₁=0.44 and r₂=0.10 (KT, ¹H NMR), r₁=0.45 and r₂=0.078 (NLR) for NIPA-MA monomer pair and r₁=0.52 and r₂=0.02, r₁=0.44 and r₂=0.04, r₁=0.51 and r₂=0.014 for NIPA-CA monomer pair, respectively. Observed tendency towards alternating copolymerization at ?50 mol% NIPA concentration in monomer feed and relatively high activity of NIPA growing radical was explained by H-bond formation between CO (anhydride) and NH (amide) fragments during chain growth reactions. Intrinsic viscosity, molecular weight and thermal behaviour of the synthesized copolymers were found to depend on the type of comonomer and the amount of NIPA units in the copolymers. These functional amphiphilic copolymers containing anion- and cation-active groups show both temperature and pH sensitivity and can be used for biological purposes as physiologically active macromolecular systems.     

Electrochemical synthesis of network polygermanes and polysilanes

Network σ-conjugated polymers, i.e., a butyl substituted network polygermane, (BuH_xGe)_n (x=0–2), a butyl substituted network polysilane, (BuH_xSi)_n (x=0–2), and an octyl substituted network polysilane, (OctH_xSi)_n (x=0–2), were synthesized by electrochemical reduction of butyltrichlorogermane, butyltrichlorosilane, and octyltrichlorosilane, respectively, for the first time. A polymer of (BuH_xGe)_n (x=0–2) had absorption which extended to 900 nm, while a polymer of (BuH_xSi)_n (x=0–2) and a polymer of (OctH_xSi)_n (x=0–2) had absorption which extended to 500 and 800 nms, respectively. It was found that the reported electrochemical method gave σ-conjugated polymers with more highly developed network structures compared to the other synthetic pathways. The structure of the polymers was successfully controlled from linear to highly developed network structures by controlling the charge for electrosynthesis.     

Cationic Carbonyl complexes of manganese(I) with diphosphines

The bromo-carbonyls fac-BrMn(CO)₃(diphos)(diphos  Ph₂P(CH₂)_nPPh₂ for n = 1(dpm), 2(dpe), 3(dpp) and 4(dbp)) react with AgClO₄ in dichloromethane solution to give the neutral fac-O₃ClOMn(CO)₃(diphos). The reaction of the latter complexes at room temperature with a variety of ligands L  phosphines (PR₃), phosphites (P(OR)₃), pyridine (Py), acetonitrile (MeCN), tetrahydrothiophene (THT) or acetone (Me₂CO) leads to the cationic species fac-[Mn(CO)₃(diphos)L]ClO₄ (or to the [Mn(CO)₄(diphos))]ClO₄, when L  CO). When L is a phosphorus ligand, the cationic fac-tricarbonyls isomerize upon heating to the mer isomers, which could only be isolated by this method for diphos  dpm, the reaction being accompanied by decomposition in the other cases. UV irradiation of the mer-[Mn(CO)₃(diphos)L]ClO₄ in the presence of a large excess of L gives the corresponding trans-[Mn(CO)₂(diphos)L₂]ClO₄.     

Complexes of the selected transition metal ions with 4-methoxycinnamic acid

In this study, 4-methoxycinnamates of Mn(II), Co(II), Ni(II), Cu(II), Cd(II), Nd(III) and Gd(III) were synthesised. From the infrared (IR) spectra analysis of complexes, sodium salt and according to the spectroscopic criteria the carboxylate groups seem to be bidentate chelating. The complexes of 4-methoxycinnamates lose the water molecules in one or two steps. The final products of their decomposition are oxides of the respective metals. The enthalpy values of dehydration process were determined. The FTIR spectra of the gas phase products indicate that the decomposition of the complexes is connected mainly with the release of molecules of water (H₂O), carbon dioxide (CO₂), carbon monoxide (CO), methane (CH₄) and other hydrocarbons. The analysed compounds follow the Curie?CWeiss law. The magnetic moment values experimentally determined change as follows: from 5.90??? _B to 6.27??? _B for Mn(II) complex, from 4.57??? _B to 4.99??? _B for Co(II) complex, from 3.68??? _B to 3.30??? _B for Ni(II) complex, from 1.87 ?? _B to 1.96 ?? _B for Cu(II) complex, from 3.06??? _B to 3.51??? _B for Nd(III) complex, and from 6.91??? _B to 6.90??? _B for Gd(III) complex.     

Synthesis and structure of alkali metal zirconium vanadate phosphates

Mixed vanadate phosphates in the systems MZr₂(VO₄) _x (PO₄)_{3 ? x} , where M is an alkali metal, were synthesized and studied by X-ray diffraction, electron probe microanalysis, and IR spectroscopy. Substitutional solid solutions with the structure of the mineral kosnarite (NZP) are formed at the compositions 0 ≤ x ≤ 0.2 for M = Li; 0 ≤ x ≤ 0.4 for M = Na; 0 ≤ x ≤ 0.5 for M = K; 0 ≤ x ≤ 0.3 for M = Rb; and 0 ≤ x ≤ 0.2 for M = Cs. Apart from the high-temperature NZP modification, lithium vanadate phosphates LiZr₂(VO₄) _x (PO₄)_{3 ? x} with 0 ≤ x ≤ 0.8 synthesized at temperatures not exceeding 840°C crystallize in the scandium tungstate type structure. The crystal structures of LiZr₂(VO₄)_0.8(PO₄)_2.2 (space group P2₁/n, a = 8.8447(6) Å, b = 8.9876(7) Å, c = 12.3976(7) Å, β = 90.821(4)○, V = 985.4(1) ų, Z = 4) and NaZr₂(VO₄)_0.4(PO₄)_2.6 (space group $R\bar 3c$ = 8.8182(3) Å, c = 22.7814(6) Å, V = 1534.14(1) ų, Z = 6) were refined by the Rietvield method. The framework of the vanadate phosphate structure is composed of tetrahedra (that are statistically occupied by vanadium and phosphorus atoms) and ZrO₆ octahedra. The alkali metal atoms occupy extra-framework sites.     

The formation and crystal and molecular structures of (η5-pentamethylcyclopentadienyl)(η5-cyclopentadienyl)dichloro-titanium, -zirconium and -hafnium

A reaction between (η⁵-C₅Me₅)TiCl₃ and C₅H₅Tl in benzene solution has afforded (η⁵-C₅Me₅)(η⁵-C₅H₅)TiCl₂ (I) in quantitative yield. (η⁵-C₅Me₅)(η⁵-C₅H₅)HfCl₂ (III) has been prepared in 83% yield from a reaction between (η⁵-C₅Me₅)HfCl₃ and C₅H₅Na·DME in refluxing toluene solution. The crystal and molecular structures of (η⁵-C₅Me₅)(η⁵-C₅H₅TiCl₂ (I), (η⁵-C₅Me₅)(η⁵-C₅H₅)ZrCl₂ (II) and (η⁵-C₅Me₅)(η⁵-C₅H₅HfCl₂ (III) have been determined from X-ray data measured by counter methods. The three compounds are isostructural, crystallizing in the orthorhombic space group Pnma. The cell constants are: (I): a 9.873(1), b 12.989(3), c 11.376(4) Å and D_calc 1.45 g cm^?3 for Z = 4; (II): a 9.930(3), b 13.231(9), c 11.628(3) Å and D_calc 1.58 g cm^?3 for Z = 4; (III): a 9.938(1), b 13.156(2), c 11.582(2) Å and D_calc 1.97 g cm^?3 for Z = 4. In each case the metal atom resides on a crystallographic mirror plane which bisects both cyclopentadienyl rings and the ClMCl bond angle. The MCl bond lengths are 2.3518(9) for I, 2.4421(9) for II and 2.415(1) Å for III. The metal—cyclopentadienyl and metal—pentamethylcyclopentadienyl bond distances average 2.38(5) and 2.42(2) Å for I, 2.50(4) and 2.53(2) Å for II, and 2.48(4) and 2.50(1) Å for III respectively.     

Thermodynamic dissociation constants of silychristin, silybin, silydianin and mycophenolate by the regression analysis of spectrophotometric data

Mixed dissociation constants of four drug acids, i.e. silychristin, silybinin, silydianin and mycophenolate at various ionic strengths I of range 0.01 and 0.30 and at temperatures of 25 and 37 °C were determined using the SQUAD(84) regression analysis program applied to pH-spectrophotometric titration data. The proposed strategy of an efficient experimentation in a protonation constants determination, followed by a computational strategy for the chemical model with a protonation constants determination, is presented on the protonation equilibria of silychristin. The thermodynamic dissociation constant pK_a^T was estimated by non-linear regression of {pK_a, I} data at 25 and 37 °C: for silychristin pK_a,1^T=6.52(16) and 6.62(1), pK_a,2^T=7.22(13) and 7.41(5), pK_a,3^T=8.96(9) and 8.94(9), pK_a,4^T=10.17(7) and 10.03(8), pK_a,5^T=11.89(4) and 11.63(7); for silybin pK_a,1^T=7.00(4) and 6.86(5), pK_a,2^T=8.77(11) and 8.77(3), pK_a,3^T=9.57(8) and 9.62(1), pK_a,4^T=11.66(3) and 11.38(1); for silydianin pK_a,1^T=6.64(7) and 7.10(6), pK_a,2^T=7.78(5) and 8.93(1), pK_a,3^T=9.66(9) and 10.06(11), pK_a,4^T=10.71(7) and 10.77(7), pK_a,5^T=12.26(5) and 12.14(5); for mycophenolate pK_a^T=8.32(1) and 8.14(1). Goodness-of-fit tests for various regression diagnostics enabled the reliability of parameter estimates to be found.     

Synthesis of octahedral carbonyl complexes of manganese(I) with SCN or CN ligands. Crystal structure of fac-[SCNMn(CO)3(dppm)]

The complexes fac-[XMn(CO)₃(dppm)], cis,cis-[XMn(CO)₂(dppm)(P(OPh)₃)] and trans-[XMn(CO)(dppm)₂] with X = SCN or CN have been prepared from the corresponding bromocarbonyls and the salts AgX or KX, or, in the case of the di- and mono-carbonyls, from fac-[XMn(CO)₃(dppm)] with X = SCN or CN by thermal or photochemical CO substitution by the ligands P(OPh)₃ or dppm. The structure of fac-[SCNMn(CO)₃(dppm)] has been determined by X-ray diffraction. The crystals are monoclinic, space group P2₁/n, and the structure has been refined to R = 0.058 for 4123 reflexions measured in the range 2 ⩽ θ ⩽ 30 at room temperature. The cis,cis-[NCMn(CO)₂(dppm)(P(OPh)₃)] complex can be oxidized and subsequently reduced to the isomer trans-[NCMn(CO)₂(dppm)(P(OPh)₃)]. All the neutral cyanide complexes react readily with MeI and KPF₆ to give the corresponding methylisocyanide derivatives [Mn(CO)₂(dppm)(P(OPh)₃)(CNMe)]PF₆ and [Mn(CO)(dppm)₂(CNMe)]PF₆. The stereochemistries of the compounds is discussed in relation to the ³¹P NMR spectra.     

Jahn-teller effects in the MNDO approximation: structures of the molecular cations of some simple organoberyllium compounds

The MNDO method gives geometries for the molecular cations of organoberyllium compounds of types BeR₂ and HBeR (R = CH₃, CHCH₂, CCH, CN, C₅H₅), of C₄H₄Be and CH₃BeBeH₃ and of the series CH_4?n(BeH)_n (n = 0–4) which have symmetries in precise accord with the predictions of the Jahn-Teller theorem. In the series CH_4?n(BeH)_n and CH_4?n(BeH)_n⁺, the barriers to inversion via a planar intermediate decrease with increasing n, are significantly smaller for the cations than for the neutral molecules, and are zero for CH(BeH)₃⁺ and C(BeH)₄⁺, both of which have their minimum energy when strictly planar at carbon.     

Crystal and molecular structures of the complexes of cobalt dichloride with 1-isopropenylimidazole and 1-vinylimidazole

The crystal and molecular structures of bis(1-isopropenylimidazole)dichlorocobalt (C₁₂H₁₆Cl₂·N₄Co) [R 0.036 (R _W 0.089) for 3229 unique reflections with I > 2σ(I)] and tetra(1-vinylimidazole)dichlorocobalt (C₂₀H₂₄Cl₂N₈Co) [R 0.031 (R _W 0.072) for 1863 unique reflections with I > 2σ(I)] were determined. In these molecular complexes, the monodentate terminal 1-alkenylimidazole ligands coordinate to the metal via a “pyridine” nitrogen atom. In C₁₂H₁₆Cl₂N₄Co, the Co atom has a distorted tetrahedral 2N,2Cl coordination. The coordination polyhedron of cobalt in C₂₀H₂₄Cl₂N₈Co is a strongly elongated 4N,2Cl octahedron. The Co-N and Co-Cl bonds [Co-N 2.015(2) and 2.032(4) Å; Co-Cl 2.229(2) Å] in the tetrahedral complex C₁₂H₁₆Cl₂N₄Co are shorter than those in the octahedral complex C₂₀H₂₄Cl₂N₈Co [Co-N 2.134(2) and 2.157(2) Å; Co-Cl 2.518(1) Å]. In the structures of both complexes there are short contacts involving the Cl atoms.     

Thermal decomposition of anionic organoaluminum compounds : V. The preparation and crystal structure of the (isopropylideneamino)dimethylaluminum dimer

The thermolysis of K[Al₂(CH₃)₆SCN] at 120° leads to the formation of [(CH₃)₂AlNC(CH₃)₂]₂. Verification of the dimeric configuration of (isopropylidenamino)dimethylaluminum has been obtained from three-dimensional X-ray data measured by counter methods. [(CH₃)₂AlNC(CH₃)₂]₂ crystallizes in the triclinic space group P$\text{1}$ with cell dimensions a 7.027(4), b 7.760(4), c 8.583(4) Å, α 115.70(5)°, β 105.72(5)°, γ 92.38(5)°, and ?_calc 0.94 g/cm³ for Z = 1. Leastsquares refinement gave a final conventional R value of 0.058 for 1230 independent reflections. Proposed structures of the parent 2/1 complex, as well as mechanisms for the formation of (isopropylidenamino)dimethylaluminum are discussed.     

Strong dependence of negative cluster ion spectra on principal quantum numbern in collisions of state-selected Ar** (n d) Rydberg atoms with N2O clusters

Electron transfer from state-selected Ar**(n d) Rydberg atoms to N₂O clusters has been studied over a broad range of principal quantum number (10 ≦n ≦ 45) and at two different Ar velocities (560 and 1000 m/s). A strongn-dependence of the negative cluster ion spectra is detected: while at highn ? 30, a rather narrow distribution of (N₂O) _q ·O^? and (N₂O) _q ^? ions around the major product (N₂O)₆·O^? is found, the distribution widens considerably towards largerq for decreasingn. Correspondingly, the effective rate constants for (N₂O) _q ·O^? and (N₂O) _q ^? formation show very differentn-dependences for lowq ≦ 6 and higherq. Possible reasons for the observed behaviour are discussed.     

The preparation and crystal structures of dicarbonylcyclopentadienylnitrosylchromium and dicarbonylfluorenylnitrosylchromium

The X-ray-crystal structures of both (η⁵-C₅H₅)Cr(CO)₂(NO) (I) and (η⁵-C₁₃H₉)Cr(CO)₂(NO) (II, η⁵-C₁₃H₉ = η⁵-9H-fluorenyl) are described. I crystallizes in the monoclinic space group P2₁/n with lattice constants a 10.998(4), b 7.066(3), c 11.940(4) Å, β 116.37(4)°, and ?_calc 1.63 g cm^?3 for Z = 4. II belongs to the orthorhombic space group Pnma with a 6.463(4), b 15.512(6), c 12.916(6) Å, and ?_calc 1.55 g cm^?3 for Z = 4. Least-squares refinement gave final conventional R values of 0.037 based on 1081 independent observed reflections for I, and 0.042 with 630 reflections for II. The carbonyl and nitrosyl groups are disordered in I, but the nitrosyl ligand in II occupies a position “trans” to the electron-rich C(9) of the fluorenyl system. Photolysis of II in liquid olefins (L) or acetyleness leads to substituted derivatives of the type (η⁵-C₁₃H₉)Cr(CO)(NO)L (L = cyclooctene, cycloocta-1,5-diene, norbornene, norbornadiene, phenylacetylene).     

The chemistry and the sterechemistry of Poly(N-Alkyliminoalanes: XIII. The crystal and molecular structure of the hexamers (ClAlN-i-Pr)6 and (Me0.83H0.17AlN-i-Pr)6MeAlN-i-Pr)6

The crystall and molecular structures of (ClAlN-i-Pr)₆ (I), and of (Me_0.83H_0.17AlN-i-Pr)₆(MeAlN-i-Pr)₆ have been determined by single crystal three-dimensional X-ray analysis. Block-matrix least-squares refinements led to conventional R factor of 0.039 for I and 0.037 for II. The compounds are isostructural, as the cage molecules consist of a prismatic hexagonal framework, (AlN)₆, similar to that observed for the parent hydrogenated analogue (HAlN-i-Pr)₆.Some differences in bond distances and angles are discussed, in connection with the different Al-bonded substituents. Crystal data: I, trigonal space group R$\text{3}$; a = 17.083(2), c = 9.652(1); Z = 3; D_c 1.46 g cm^?3; II, trigonal space group R$\text{3}$, a = 17.378(3), c = 9.706(3) »; Z = 3; D_c 1.15 g cm^?3.     

The sign of the Co quadrupole splitting in Co(III) compounds,and the magnitude of the Fe quadrupole moment

Using the partial quadrupole splitting values (PQS) for ligands such as Cl⁻, CN⁻ and NH₃ derived from Mössbauer spectra of Fe(II) low spin compounds, the sign of V_zz is obtained for (e²qQ)_Co in isoelectronic compounds of Co(III) low spin. The predicted signs of V_zz are: trans- [Co(NH₃)₄Cl₂]⁺, positive; [Co(NH₃)₅Cl]⁺⁺, positive, and [Co(NH₃)₅CN]⁺⁺, negative. A value of the ⁵⁷Fe quadrupole moment of 0.16 ± 0.03 has been determined by comparing the observed e²qQ values for the above Co(III) compounds with these calculated from PQS values for the corresponding hypothetical Fe(II) compounds.