Regular Octahedral Geometry Research Articles

Synthesis and crystal structure of the complex [(CH 3C(CH 2PPh 2) 3)Rh(CH 3C(CH 2S) 3]·0.5THF

The novel complex [(CH 3C(CH 2PPh 2) 3)Rh(CH 3C(CH 2S) 3)]·0.5THF containing the related tripod ligands CH 3C(CH 2PPh 2) 3 (triphos) and CH 3C(CH 2S) 3 3− (trithiol) has been prepared and its molecular structure has been determined by single crystal X-ray analysis. Space group P2 1/n, a = 14.188(3), b = 15.917(6), c = 21.735(4) A ̊ , β = 91.12(3) ° and Z = 4 . Each tripod ligand coordinates to the metal with all the three donor atoms in an almost regular octahedral geometry.

Calcium Potassium Tris(oxalato-O1,O2)chromate(III) Pentahydrate

The CrIII atom in CaK[Cr(C2O4)3].5H2O, has a regular octahedral geometry with three oxalato groups completing the coordination. Both the calcium and potassium cations are coordinated to the O atom of the oxalate group.

Crystal Structure of N,N-Dimethylthioformamide Solvates of the Divalent Group 12 Ions with Linear Coordination Geometry for Mercury(II), Tetrahedral for Zinc(II), and Octahedral for Cadmium(II).

The crystalline solvates of the divalent group 12 metal ions with the soft sulfur donor N,N-dimethylthioformamide display an unusual variation in coordination number and geometry with two, four, and six ligands attached to the mercury(II), zinc(II), and cadmium(II), ions, respectively. Bis(N,N-dimethylthioformamide)mercury(II) perchlorate precipitates from acetonitrile solution when adding less than 2 equiv of N,N-dimethylthioformamide, while the zinc and cadmium solvates crystallize from saturated N,N-dimethylthioformamide solutions. The disolvate [Hg(SCHN(CH(3))(2))(2)](ClO(4))(2) crystallizes in the monoclinic space group P2(1)/n (No. 14) with a = 6.208(1) Å, b = 15.239(7) Å, c = 8.681(2) Å, beta = 99.30(3) degrees, and Z = 2. Centrosymmetric mercury(II) complexes with strong collinear bonds to two N,N-dimethylthioformamide molecules, Hg-S 2.350(2) Å, are joined by double bridges of perchlorate ions in chains along the a-axis by four weak interactions between the mercury and the perchlorate oxygen atoms, mean Hg-O distance 2.84 Å. Tetrakis(N,N-dimethylthioformamide)zinc trifluoromethanesulfonate, [Zn(SCHN(CH(3))(2))(4)](CF(3)SO(3))(2), crystallizes in the triclinic space group P&onemacr; (No. 2) with a = 10.487(3) Å, b = 12.910(3) Å, c = 13.489(5) Å, alpha = 68.800(4) degrees, beta = 69.260(4) degrees, gamma = 74.06(1) degrees, and Z = 2, with the zinc ions tetrahedrally surrounded by four N,N-dimethylthioformamide ligands, mean Zn-S distance 2.34 Å. Also the cadmium solvate of corresponding composition, [Cd(SCHN(CH(3))(2))(4)(CF(3)SO(3))(2)], crystallizes in the space group P&onemacr;, with a = 8.670(1) Å, b = 9.529(1) Å, c = 10.685(1) Å, alpha = 75.20(1) degrees, beta = 66.97(1) degrees, gamma = 65.31(1) degrees, and Z = 1, although the structure comprises centrosymmetric tetrakis(N,N-dimethylthioformamide)bis(trifluoromethanesulfonato)cadmium(II) complexes in which four Cd-S bonds (mean 2.65 Å) and two weaker Cd-O bonds at 2.470(2) Å to the trifluoromethanesulfonate ions give rise to a pseudo-octahedral coordination around the cadmium ion. When using perchlorate instead as counterion, hexakis(N,N-dimethylthioformamide)cadmium perchlorate, [Cd(SCHN(CH(3))(2))(6)](ClO(4))(2), crystallizes in the space group P2(1)/n with a = 12.757(1) Å, b = 7.4681(6) Å, c = 19.732(2) Å, beta = 96.31(1) degrees, and Z = 2. The mean Cd-S bond distance increases to 2.715 Å in the fully solvated cadmium ion with almost regular octahedral coordination geometry to its six centrosymmetrically related ligands. The effect of the weak internal hydrogen bonding occuring between the hydrogen atom of a -CHS group and the sulfur atom of neighboring N,N-dimethylthioformamide ligands is discussed.

The preparation and characterization of bis-chelated nickel(II) complexes of the 6-methylpyridine-2-carboxaldehyde Schiff bases of S-alkyldithiocarbazates and the X-ray crystal structure of the bis {S-methyl- β- N- (6-methylpyrid-2-yl)- methylenedithiocarbazato}nickel(II) complex

New nickel(II) complexes of general formula, [Ni(NNS) 2] (NNS − = uninegatively charged tridentate ligands formed by condensation of 6-methyl-2-formylpyridine with S-methyl- and S-benzyldithiocarbazates) have been prepared and characterized by a variety of physico-chemical techniques. Magnetic and spectroscopic evidence support a distorted octahedral structure for these complexes. The crystal and molecular structure of the bis{S-methyl- β- N-(6-methylpyrid-2-yl)methylenedithiocarbazato}nickel(II) complex has been determined by X-ray diffraction studies. The complex has a distorted octahedral structure with the ligands coordinated to the nickel(II) ion as uninegatively charged tridentate chelating agents via the pyridine nitrogen, the azomethine nitrogen and the mercaptide sulphur atoms. The distortion from the regular octahedral geometry is ascribed to the stereochemical limitations imposed by the planar tridentate ligands.

An Adduct of Magnesium Sulfate with a Member of the Quinolone Family (Ciprofloxacin)

In the title compound, 4-(3-carboxy-1-cyclopropyl-6-fluoro-1,4-dihydro-4-oxo-7-quinolinyl)-1- piperazinium—magnesium hexahydrate—sulfate—water(1/0.5/1/3), (C17H19FN3O3)[Mg(H2O)6]0.5SO4.3H2O, the Mg2+ ion lies on a twofold axis and adopts a nearly regular octahedral geometry. The quinolone is protonated at the terminal N atom of the piperazine residue. The H atom of the carboxylic group is hydrogen bonded to the carbonyl O atom, thus preventing the bonding of the metal to this part of the molecule.

Synthesis and x-ray structure of zinc(II) derivatives of esters of 2-pyridinecarboxylic acid

Zinc(II) halides form a series of of 1:1 and 1:2 compexes with neutral 2-pyridinecarboxylate esters, which act as bidentate nitrogenoxygen donors, via reaction in alcohol solution. Compounds of formula [ZnX 2(C 5H 4NCOOR) n ] with n = 1 (X = Cl, R = Me, Et, Pr 1 and X = Br, R = Et) and the whole series with n = 2 (x = Cl, Br, I and R = Me, Et, Pr i) have been obtained. The crystal structures of five complexes, [ZnX 2(C 5H 4NCOOPR i) 2] (X = Cl, Br or I) and [ZnX 2(C 5H 4NCOOMe) 2] (X = Br or I), have been determined. In all cases the structure consists of discrete neutral monomeric units where the zinc atom has a distorted octahedral coordination to two halides, in cis disposition, and to two 2-pyridinecarboxylate ester ligands by means of the pyridine nitrogen and the carbonyl oxygen atoms. The degree of distortion from regular octahedral geometry is compared to closely related structures.

A dicopper (II) complex of a new octaaza macrocycle: a receptor in the entatic state

In the crystallographically characterized macrocyclic complex [Cu2L(MeCN)2][F3CSO3]4·2 MeCN the copper ions adopt a highly distorted five-coordinate geometry; relaxation to a more regular octahedral geometry on incorporation of a bridging substrate is demonstrated by the structure of [Cu2L(µ-CN)(MeCN)2][ClO4]3.

Synthesis, spectroscopic and structural characterization of the mer isomer of ammonium bis(phenylpyruvic acid thiosemicarbazone)-cobalt(III) hemihydrate

Phenyl pyruvate thiosemicarbazone (H2PPVATSC) coordinates in its binegative thiolate form to cobalt(III) in the complex isolated from basic medium. An X-ray structure determination of the resulting meridional isomer was found to contain mutually cis sulphur, trans nitrogen, and trans oxygen donor atoms, respectively. The two five-membered rings formed by each ligand are puckered towards each other, resulting in a distortion from regular octahedral geometry about the cobalt atom. The complex was found to exhibit only a metal-based one electron reversible reduction at -0.97 V, while the parent ligand yields a c.v. profile consisting of two irreversible reduction peaks at -0.75 and -1.05V respectively, the latter corresponding to the reduction of the azomethine group.

1,4,7-Tris(2,2′-bipyridyl-5-ylmethyl)-1,4,7-triazacyclononane (L1), a powerful tris(2,2′-bipyridyl) chelating macrocyclic ligand. X-Ray structure of [Ru(L1H)][PF6]3, a complex containing a strongly trapped proton

A new powerful tris(2,2′-bipyridyl) chelating ligand, 1,4,7-tris(2,2′-bipyridyl-5-ylmethyl)1,4,7-triazacyclononane (L1), has been synthesised and characterised, and an X-ray structure of [Ru(L1H)]3+ obtained; in the complex all three bipyridyl groups are coordinated, with a fairly regular octahedral RuII geometry, and although the azamacrocyclic nitrogen-atoms are non-coordinating to RuII, in aqueous solution they trap a single proton in the cavity between the macrocycle and the RuII, and which cannot be removed even at high pH.

Crown thioether chemistry of tin(IV): formation and crystal and molecular structures of 3SnCl4·2[9]aneS3and 2SnCl4·[18]aneS6·MeCN ([9]aneS3= 1,4,7-trithiacyclononane; [18]aneS6= 1,4,7,10,13,16-hexathiacyclooctadecane)

Reactions of tin(IV) chloride with selected thiacrown ligands in acetonitrile have been studied. With [9]aneS3(1,4,7-trithiacyclononane) the yellow compound 3SnCl4·2[9]aneS3 has been isolated and structurally characterised by X-ray diffraction: orthorhombic, space group Pbca, a= 11.245(5)Å, b= 12.927(6)Å. c= 23.779(10)Å, Z= 4, at 230(2) K. The structure consists of six-co-ordinate [SnCl3([9]aneS3)]+ cations and [SnCl6]2– anions in the ratio 2 : 1. In the cation the thiacrown is chelated facially to a SnCl3 unit with Sn–Cl 2.369(4)(mean), Sn–S 2.637(4)Å(mean). The [SnCl6]2– counter anions exhibit a regular octahedral geometry with Sn–Cl 2.448(4)(mean)Å. The reaction with [18]aneS6(1,4,7,10,13,16-hexathiacyclooctadecane) provides yellow crystals of the adduct 2SnCl4·[18]aneS6·MeCN the structure of which has also been determined by X-ray diffraction; monoclinic, space group C2, a= 16.901 (5), b= 12.968(5), c= 7.284(3)Å, β= 100.50(3)°, Z= 2, at 240(2) K. The structure consists of two SnCl4 units located at opposite ends of the ring cavity with one above and the other below the ring plane. Each tin atom is six-co-ordinate and is attached to the ring via cis chelation of two sulfur atoms.

Electrochemical, spectroscopic and structural characterization of the mer isomer of ammonium bis(pyruvic acid thiosemicarbazone)cobalt(III)·benzene

The crystal structure is reported of ammonium bis(pyruvic acid thiosemicarbazone)cobalt(III)·benzene, CoS 2O 4N 6C 16H 16, which forms dark red triclinic crystals with unit cell parameters: a=9.307(2), b=9.555(2), c=14.729(3) Å, α=67.04(1), β=118.89(2), γ=79.09(1)°, V=932.9(2) Å 3, space group P 1 . The final R factor for 3948 observed reflections is 3.1%. The distorted octahedral complex is held together by a hydrogen bonding system involving the ammonium and amine protons and the carboxylate oxygen and imine nitrogen atoms. The coordination polyhedron around the cobalt atom in the complex anion [Co(PVATSCH) 2] − is highly distorted from regular octahedral geometry as evidenced by the fact that the bond angles about the cobalt atom range from 83.40(6) to 96.75(5)°. The isolated meridional isomer contains a cis placement of the sulfur donor atoms with puckered ligand moieties arising from the non-planar hydrazinic chain with a folding angle of ca. 4° across the sulfur-nitrogen and oxygen-nitrogen atoms. The ligand H 2PVATSC provides a strong ligand field and thus results in a low spin cobalt(III) complex. The complex undergoes a reversible one-electron reduction at the metal center.

Structure of tetraaquacobalt(II) bromide dihydrate (cobalt bromide hexahydrate)

Tetraaquacobalt(II) bromide dihydrate, [Co(H2O)4]Br2 x 2H2O, Mr = 326.83, monoclinic, C2/m, a = 11.0158(12), b = 7.1694(10), c = 6.9111(10) A, beta = 124.761(7)degrees, V = 448.4(1) A3, Z = 2, F(000) = 314, Dx = 2.420 g cm-3, lambda(Mo K alpha) = 0.71069 A, T = 296 K, mu = 107.13 cm-1, R = 0.022 for 532 unique reflections having I greater than 0. The single type of Co ion is octahedrally coordinated by four equivalent water-molecule O atoms at the observed distance 2.081(2) A and two equivalent Br ions at the observed distance 2.6048(5) A in an array which, with respect to its angles, departs only slightly from regular octahedral geometry. The cobalt-oxygen-bromine complex was found to manifest rigid-body behavior. The cobalt-oxygen distance corrected for rigid-body motion was found to be 2.088 A; the corrected cobalt-bromine distance, 2.6081 A. Associated with each complex are two water molecules of hydration. Assignment and refinement of the coordinates of the four non-equivalent H atoms permitted detailed analysis of the hydrogen bonding, which involves each of the four non-equivalent H atoms significantly. The structure as determined in this study differs markedly from that presented in the sole published single-crystal study [Stroganov, Andreev, Kozina & Solov'ev (1961). Vestn. Leningr. Univ. Ser. Mat. Fiz. Khim. 16, 114-119]. In particular, the space-group assignment differs and the pattern of bromine-oxygen distances is quite different. Contrary to Stroganov et al., this structure is isomorphic with that of cobalt chloride hexahydrate.

Interaction of Purine Nucleotides with Inert Paramagnetic Cr(III) Probes Evaluated by NMR Relaxation Effects. Molecular Mechanics Calculations on Cr(III) and Co(III) Polyphosphate Complexes

The 1H NMR relaxation effects produced by paramagnetic Cr(III) complexes on nucleoside 5'-mono- and -triphosphates in D2O solution at pH' = 3 were measured. The paramagnetic probes were [Cr(III)(H2O)6]3+, [Cr(III)(H2O)3(HATP)], [Cr(III)(H2O)3(HCTP)] and [Cr(III)(H2O)3(UTP)-, while the matrix nucleotides (0.1 M) were H2AMP, HIMP-, and H2ATP2-. For the aromatic base protons, the ratios of the transverse to longitudinal paramagnetic relaxation rates (R2p/R1p) for the [Cr(III)(H2O)6]3+/H2ATP2-, [Cr(III)(H2O)3(HATP)]/H2ATP2-, [Cr(III)(H2O)3(HCTP)]/H2ATP2 and [Cr(III)(H2O)3(UTP)]-/H2ATP2 systems were below 2.33 so the dipolar term predominates. For a given nucleotide, R1p for the purine H(8) signal was larger than for the H(2) signal with the [Cr(III)(H2O)6]3+ probe, while R1p for the H(2) signal was larger with all the other Cr(III) probes. Molecular mechanics computations on the [Cr(III)(H2O)4(HPP)(alpha,beta)], [Cr(III)(NH3)4(HPP)(alpha,beta)], [Co(III)(NH3)3(H2PPP)(alpha,beta,gamma)] and [Co(III)(NH3)4(HPP)(alpha,beta)] complexes gave calculated energy-minimized geometries in good agreement with those reported in crystal structures. The molecular mechanics force constants found were then used to calculate the geometry of the inner sphere [Cr(III)(H2O)6]3+ and [Cr(III)(H2O)3(HATP)(alpha,beta,gamma)] complexes as well as the structures of the outer sphere [Cr(III)(H2O)6]3(+)-(H2AMP) and [Cr(III)(H2O)6]-(HIMP)- species. The gas-phase structure of the [Cr(III)(H2O)3(HATP)(alpha,beta,gamma)] complex shows the existence of a hydrogen bond interaction between a water ligand and the adenine N(7)(O...N = 2.82 A). The structure is also stabilized by intramolecular hydrogen bonds involving the -O(2')H group and the adenine N(3) (O...N = 2.80 A) as well as phosphate oxygen atoms and a water molecule (O...O = 2.47 A). The metal center has an almost regular octahedral coordination geometry. The structures of the two outer-sphere species reveal that the phosphate group interacts strongly with the hexa-aquochromium probe. In both complexes, the nucleotides have a similar "anti" conformation around the N(9)-C(1') glycosidic bond. However, a very important difference characterizes the two structures. For the (HIMP)- complex, strong hydrogen bond interactions exist between one and two water ligands and the inosine N(7) and O(6) atoms, respectively (O...O = 2.63 A; O...N = 2.72, 2.70 A). For the H2AMP complex, the [Cr(III)(H2O)6]3+ cation does not interact with N(7) since it is far from the purine system. Hydrogen bonds occur between water ligands and phosphate oxygens. The Cr-H(8) and Cr-H(2) distances revealed by the energy-minimized geometries for the two outer sphere species were used to calculate the R1p values for the H(8) and H(2) signals for comparison with the observed R1p values: 0.92(c), 1.04(ob) (H(8)) and 0.06(c), 0.35(ob) (H(2)) for H2AMP; and 3.76(c), 4.53(ob) (H(8)) and 0.16(c), 0.77(ob) s-1 (H(2)) for HIMP-.(ABSTRACT TRUNCATED AT 400 WORDS)

Structural characterization of the manganese(IV) Schiff-base complex MnIV(5-Cl-SALAHP)2

Bis[3-(5-chlorosalicylideneamino)propanolato-O,N,O']manganes e(IV) methanol solvate, [Mn(C10H10ClNO2)2].CH3OH, Mr = 510.3, monoclinic, P2(1)/c, a = 11.949 (2), b = 7.530 (2), c = 25.777 (6) A, beta = 105.75 (2) degrees, V = 2232.4 (8) A3, Z = 4, Dx = 1.518 g cm-3, lambda(Mo K alpha) = 0.7107 A, mu = 7.98 cm-1, F(000) = 1502, T = 300 K, R = 0.0343, wR = 0.032 for 2113 unique reflections with (I) greater than 3 sigma(I). The title complex MnIV(5-Cl-SALAHP)2 [5-Cl-SALAHP = 3-(5-chlorosalicylideneamino)propanolato] displays a regular octahedral geometry. The 5-Cl-SALAHP ligand is tridentate, forming a meridional chelate with one phenolato oxygen (Mn-Oavg = 1.90 A), one alkoxide oxygen (Mn-Oavg = 1.85 A) and one imine nitrogen (Mn-Navg = 2.02 A) coordinated to the metal. Important angles described by the six atoms bound to manganese are all very close to either 180 or 90 degrees except the N-Mn-N angle which is 174.7 degrees. Previous studies have shown that MnIV(5-Cl-SALAHP)2 displays a rhombic EPR spectrum with well-resolved 55Mn hyperfine structure on gx, gy and gz. In contrast, Mn(SALADHP)2 [SALADHP = 2-methyl-2-(salicylideneamino)-1,3-propanediolato] shows a broad, ill-defined signal at g = 5.15 and a weak g = 2 component. The different spectral forms result from the extent of distortion of the MnIV octahedron. The reported structure is of potential importance to the understanding of the photosynthetic water-oxidizing system.

Regular Octahedral Coordination of As(III) in the Anion [As3Br12]3- Structural Correlation of the Antibonding Influence of the As 4s-Orbital in Bromoarsenates(III)

The bromoarsenates(lll) [Et4N]3[As3Br12] (1). [Ph4P]2[As2Br8] (2), [(n-prop)4N]2[As2Br8] (3) and {[pipH]3[As2Br9] · [pipH]Br} (4) have been prepared and their structures established by X-ray structural analysis. The central As atom in the novel face-bridged trioctahedral species [As3Br12] displays an effectively regular octahedral coordination in one of the two independent anions in the unit cell of 1. The As-Br distances are 2.671 (1) - 2.672(2) Å with Br-A s-Br angles in the range 88.8(1)-91.2(1)°. In contrast the outer As atoms exhibit a severely distorted octahedral geometry with three short As - Br terminal bonds (2.404(2)-2.409(2) Å). The [As2Br8]2- anions in 2 and 3 are centrosymmetric with the As atoms displaying a square-pyramidal coordination. A structural correlation of opposite As-Br distances in the linear three-centre Br-As···Br interactions is presented. The sum of the bond valences in bromoarsenates(III) is a minimum for the regular octahedral geometry, reflecting, thereby, the influence of the As 4s-orbital in the antibonding 2a1g MO. An empirical expression for As-Br distances in bromoarsenates(III) is derived.

Sulphonamide nitrogen-containing, nitrogen-protected amino acids interacting with the Cd2+ion. A cadmium-113 nuclear magnetic resonance and potentiometric study. X-Ray diffraction of [Cd(ts-β-alaO)2(H2O4)

α-Alanine and β-alanine, N-protected by a tosyl (toluene-p-sulphonyl) group, bind Cd2+ acting initially as a simple carboxylate at low pH, and, at increasing pH, as N,O-bidentate ligands, through the carboxylic oxygen and the deprotonated amide nitrogen atoms. In the latter case they give rise to five- and six-membered ring chelate species, respectively. Cadmium-113 n.m.r. and potentiometric measurements reveal that the stability of the complexes is almost unaffected by the chelate ring size. The five-membered ring chelate species has a more deshielded chemical shift and only a slightly greater stability than the six-membered species. The crystal and molecular structures of the [Cd(ts-β-alaO)2(H2O)4](ts-β-alao =N-tosyl-β-alaninate monoanion) complex have been solved. Crystal data are: monoclinic, space group P21/c, a= 14.956 (6), b= 5.472(2), c= 16.860(7)Å, β= 107.36(3)°, Z= 2, and R= 0.039 for 1 635 reflections. The amina acid molecule binds through the unidentate carboxylate group and the structure consists of discrete units in which the Cd2+ exhibits a nearly regular octahedral geometry.

X-Ray crystal structure identification of the ternary complex MgCl2·2SbCl3·6MeCN

The solid-state structure of MgCl2·2SbCl3·6MeCN has been determined by X-ray diffraction studies as the ionic salt [Mg(MeCN)6][(SbCl4)2]. Crystals of hexakis(acetonitrile)magnesium(II) bis[tetrachloroantimonate(III)] are triclinic, space group P with a= 8.968(8), b= 10.220(11), c= 8.389(9)A, α= 97.1(1), β= 79.8(1), γ= 78.1(1)°, and Z= 1.2 165 Independent reflections above background have been measured on a diffractometer and the structure refined to R 0.070. In the centrosymmetric [Mg(MeCN)6]2+ cation, the six-co-ordinate magnesium atom has a regular octahedral geometry with independent Mg–N distances of 2.136(9), 2.134(7), and 2.179(8)A. The [SbCl4]– units are polymeric. There are three short Sb–Cl bonds in a fac arrangement [Sb–Cl(1) 2.433(2), Sb–Cl(3) 2.431(2), Sb–Cl(4) 2.367(3)A]. Two SbCl3 moieties are bridged via two weaker bonds [Sb–Cl(2) 3.006(3), Sb–Cl(2′) 2.822(4)A] over a centre of symmetry to give [Sb2Cl8]2– units. These units are connected via a further weak contact Sb–Cl(1″) 3.580(2)A to give a polymeric chain. The environment of the antimony atom is distorted octahedral and there is no evidence for a stereochemically active lone pair of electrons around the antimony centres.

ChemInform Abstract: Cyano Derivatives of Some Organochlorophosphate(V) Ions.

AbstractReaction of excess AgCN with the organochlorophosphates (I) leads to the formation of the tricyanophenylphosphate (IIa) (all three isomers) and of pentacyanomethylphosphate (IIb).

The Crystal and Molecular-Structure of Two Complexes of Cobalt(III) With Pentaaza Macrocyclic Ligands Chloro (1,4,7,10,14-pentaazacycloheptadecane)cobalt(III) Bromide Chloride Hydrate [Co(C12H29N5)Cl] (Br0.33Cl1.67)H2O and Bromo(1,4,7,11,15-pentaazacyclooctadecane)cobalt(III) Bromide [Co(C13H31N5)Br]Br2

The structures of the compounds chloro (1,4,7,10,14-pentaazacycloheptadecane) cobalt(III) bromide chloride hydrate, [Co( chad )Cl] ( Br0.33Cl1.67)H2O(1) and bromo (1,4,7,11,15-pentaazacyclooctadecane) cobalt(III) bromide, [Co( coad )Br]Br2(2),have been determined by X-ray diffractometry. [Compound (1) orthorhombic, space group P bac, a 1208.5, b 2305.5, c 1318.9 pm, Z 8, R 0.056, Rw 0.071 for 1943 reflections. Compound (2), triclinic, space group P1, a 930.8, b 953.5, c 1120.3pm, α 84.60,β 398.82, γ 105.26�, Z 2, R 0.045, RW0.054 for 4821 reflections.] The compounds have structures with two ( chad ) or three ( coad ) six-membered chelate rings in the equatorial (N4) plane, but with different configurations of the chiral nitrogen centres ; chad : 1SR , 4SR, 7RS, 10RS, that is, with only the NH group at the junction of the two six-membered chelate rings on the same side of the N4 plane as the axial nitrogen; coad : 1 RS, 7SR, 11 SR, 15RS, that is, with NH groups of the central six-membered chelate ring on the same side of the N4 plane as the axial nitrogen, and the others on the opposite side. The chad compound has regular octahedral geometry, with one chair and one boat conformation six-membered chelate ring. The coad compound has distorted octahedral geometry, with long Co-N distances in the N4 plane, attributed to intra-ligand interactions.

Structure and Magnetism of Cs2KCr(CN)6 at Very Low Temperatures

The structure of the elpasolite Cs2KCr(CN)6 has been determined at 7.0 K by neutron diffraction. 877 unique reflections refined to Rw = 0.020, Χ = 1.4. The Cr(CN)6 unit is close to regular octahedral coordination geometry, with bond lengths of 207.4(4) for Cr-C and 116.6(6) pm for C-N. The C-Cr-C angles average to 90.0(5)� and the Cr-C-N angles to 178.3(1)�. The magnetic susceptibility as a function of temperature and the magnetization as a function of magnetic field strength correspond to the 4A2g ground term perturbed by a small magnetic exchange effect.