Rudolf A. G. de Graaff

High-spin α low-spin transition in [Fe(NCS)2(4,4′-bis-1,2,4-triazole)2](H2O). X-ray crystal structure and magnetic, mössbauer and EPR properties

Abstract The FeII ion in [Fe(NCS)2(4,4′-bis-1,2,4-triazole)2](H2O) has distorted tetragonal symmetry with two trans-oriented NCS− ligands. It shows a very abrupt high-spin α low-spin transition at 123.5 K on cooling and 144.5 K on warming. The compound is rather stable in vacuo at room temperature; however, samples which have passed the spin transition once lose their water of hydration above 240 K in vacuo. The dehydrated substance does not show a spin transition; it is high spin in the whole temperature range. Mossbauer ligand-field spectra and magnetic behaviour of both the hydrated and non-hydrated compounds are discussed. The spin transition has been followed by EPR measurements with the aid of traces of Cu2+ ions which could be substituted for Fe2+ in the tetragonal structure. In the high-spin phase the EPR signal is very broad and featureless; in the diamagnetic low-spin phase it is very sharp and resolved in hyperfine and superhyperfine structures. This unusual method to follow the spin transition was shown to be quite generally applicable. In the crystal structure of Fe(NCS)2(C4H4N6)2(H2O) the distances FENCS are 2.125(3) A, and FeN(ligand) 2.180(3) and 2.188(2) A. The water molecule is connected to the non-coordinating ligand N-atom by hydrogen bonding.

Synthesis and co-ordination chemistry of a novel dinucleating chelating triazole ligand. The crystal structure of bis-µ-[4-amino-3,5-bis(pyridin-2-yl)-1,2,4-triazole-N′, µ-N1,µ-N2,N″,]-bis[aquachloro-nickel(II)] dichloride tetrahydrate

Reaction of 4-amino-3,5-bis(pyridin-2-yl)-1,2,4-triazole (abpt) with nickel(II) and cobalt (II) salts produces dinuclear co-ordination compounds. One of the compounds, [Ni2(abpt)2Cl2(H2O)2]Cl2·4H2O, crystallizes in the triclinic space group P with a= 6.840(2), b= 10.199(4), c= 12.480(3)A, α= 78.62(3), β= 76.47(2), γ= 84.17(3)°, and Z= 1. Refinement based on 4 015 independent reflections yielded a value for R′ of 0.034. The dinuclear Ni2(abpt)2 unit is almost planar. The nickel ions are co-ordinated by four nitrogen atoms with N–Ni–N angles of 93.00(4), 76.74(4), 113.67(4), and 76.47(4)° and Ni–N distances of 2.013(1), 2.029(1), 2.155(1), and 2.164(1)A. The axial ligands are a water molecule and a chloride ion. The co-ordination of the metal centres is rhombically distorted octahedral. The uncommon ligand-field spectrum is interpreted along with these findings. Variable-temperature magnetic susceptibility measurements for analogous compounds of NiII and CoII with BF4–, Cl–, or Br– anions revealed that a relatively weak antiferromagnetic exchange is present in these compounds.

Recent advances in the CRANK software suite for experimental phasing

Recent developments in the CRANK software suite for experimental phasing have led to many more structures being built automatically.

Acid–base chemistry of polypyridyl ruthenium compounds of (pyridin-2′-yl)-1,2,4-triazoles. X-Ray crystal structure of bis(2,2′-bipyridine)[3-methyl-5-(pyridin-2′-yl)-1,2,4-triazolato-N1]ruthenium hexafluorophosphate tetrahydrate

The acid–base chemistry of the two co-ordination isomers of the complex of bis(2,2′-bipyridyl)-ruthenium(II)[Ru(bipy)2]2+ with 3-(pyridin-2′-yl)-1,2,4-triazole (HL1) and of the analogous compound with 3-methyl-5-(pyridin-2′-yl)-1,2,4-triazole (HL2) has been investigated. As expected the ligands act as stronger acids after binding to the Ru(bipy)2 moiety. The two co-ordination isomers of the HL1 compound show distinctly different pKa values of 4.07 ± 0.05 and 5.95 ± 0.05. Luminescence titrations and lifetime measurements indicate that both ligands are stronger acids in the excited state than in the ground state. This suggests that they act as spectator ligands and are not directly involved in the photophysical processes. The crystal structure of [Ru(bipy)2L2]PF6·4H2O has been determined by single-crystal X-ray diffraction. Crystal data: trigonal, space group P31 with a=b= 1 3.760(6), c= 30.503(9)A, α=β= 90.00, γ= 120.00°, and Z= 6. The refinement based on 4 288 unique reflections [I > 2σ(I)] yielded a R(R′) value of 0.036(0.049). The pyridyltriazole ligand is co-ordinated to ruthenium via the N1 atom of the triazolato ring. The Ru–N distances are between 2.050(5) and 2.086(4)A. Four water molecules have been located near the pyridyltriazole ligand, giving rise to an extended hydrogen-bridged, structure.

An unusual hexafluorosilicato-bridged chain compound; crystal structure of catena-(μ-Hexafluorosilicato)-tetrakis(5-phenylpyrazole)copper(II)

Abstract The reaction of a methanolic solution of M(II)(BF 4 ) 2 salts and 3(5)-phenylpyrazool (ppzH) in glass vessels yields chain compounds of general formula M(II)(ppzH) 4 (SiF 6 ) (M  Co, Ni, Cu), in which the SiF 6 2− group is the bridging ligand. The compounds can also be prepared starting from the hydrated hexafluorosilicates. The structure of one of these compounds, i.e. catena -(μ-hexafluorosilicato)-tetrakis(5-phenylpyrazole)copper(II) Cu(C 9 H 8 N 2 ) 4 (SiF 6 ) ( I ) has been determined from X-ray diffraction data. The crystals are triclinic, space group P 1 lattice constants a =5.531(7), b =12.211(5), c =12.140(7) A, α=121.69(5), β=99.30(4), γ=101.73(3)°, Z =2. The Cu(II) ions are at special positions 0,0,0 and 1 2 , 1 2 , 1 2 and are linked by bridging SiF 6 2− groups. The copper ions are coordinated by four pyrazole nitrogen atoms and the fluorine atoms of the SiF 6 2− group as axial ligands. CuN pyr distances are 2.002(5) and 1.992(5) A for Cu(1) and 2.009(5) and 1.994(5) A for Cu(2). CuF distances are 2.251(3) A for Cu(1) and 2.245(3) A for Cu(2). Magnetic susceptibility measurements of I and the analog compounds Ni(C 9 H 8 N 2 ) 4 (SiF 6 ) ( II ) and Co(C 9 H 8 N 2 ) 4 (SiF 6 ) ( III ) show no significant magnetic interaction. The magnetic and spectroscopic properties of the compounds are discussed in relation to their structure.

Syntheses, spectroscopic and magnetic properties and X-ray crystal structure of two dinuclear copper(II) compounds with the ligand N3-salicyloyylpyridine-2-carboxamidrazonato

Abstract The crystal structures, spectroscopic and magnetic properties of two dinuclear copper(II) coordination compounds containing the ligand N3-salicyloylpyridine-2-carboxamidrazonato (abbreviated as spa) are reported. Compound 1, bis[(N3-salicyloylpyridine-2-carboxamidrazonato-N1,N2O)aquacopper(II)nitrate], [Cu(spa)(H2O)(No3)]2, Cu2C26H26N10O12, crystallizes in the triclinic space group P 1 , with , a = 8.898(1), b = 12.472(4), c = 14.063(5) A , α = 91.15(3), β = 97.48(2), γ = 102.25(2)°, V = 1511.8 A 3 and Z = 2 (dinuclear units). The least-squares refinement based on 3147 reflections, with I>2σ(I), converged to R = 0.0501 and Rw = 0.0581. Two crystallographic independent five-coordinated copper(II) atoms are present in this structure, which differ slightly in bond distances and angles. Both metal ions are in a squares pyramidal environment of which the basal plane is formed by two nitrogen and an oxygen donor atom of the spa ligand and a water molecule. A nitrate anion occupies the apical position. The mononuclear fragments of symmetry related metal ions are linked in dinuclear units via a four-fold hydrogen bonding network, with Cu1Cu 1′ (1-x,1 −y, 1-z)=4.723(2) A and Cu 2 Cu 2″ (−x, −y, −z)=4.616(2) A . Compound 2, bis[(N3-salicyloylpyridine-2-carboxamidrazonato-N1,N2,O)diaquacopper(II)]diperchlorate, [Cu(spa)(H2O)2]2(ClO4)2, Cu2C26H30N8O16Cl2, crystallizes in the triclinic space group P 1 , with a = 7.138(1), b = 10.655(2), c = 12.844(1) A , α = 103.71(1), β = 98.43(1), γ = 102.19(2)°, V = 907.4 A and Z = 1 (dinuclear unit). The least-squares refinement based on 3022 reflections, with P>2σ(I), converged to R = 0.0359 and Rw = 0.0475. The copper(II) ion is in a distorted octahedron, with two N and an O donor atom of the spa ligand and a water molecule in the equatorial plane. An additional water molecule and a phenol-O are in the axial positions. There is an intramolecular stacking of two [Cu(spa)(H2O)2] units, with CuCu′ (1-x, −y, −z)=6.2810(7) A . The X-band powder EPR spectra for [Cu(spa)(H2O)(NO3)]2 show the usual spectrum for copper(II) ions in an axial symmetry. For [Cu(spa)(H2O)2]2(ClO4)2 the signals at g = 4.04, 3.02, 2.08 and 1.66, give evidence for Cu … Cu exchange splittings, although the magnetic interaction is extremely weak and could not be detected by magnetic susceptibility measurements over the temperature range 10–280 K.

Spectroscopic and magnetic properties of cobalt(II) and nickel(II) clusters obtained from 1-(hydroxymethyl)-3,5-dimethylpyrazole. X-Ray structure of tetrakis[chloro(µ3-3,5-dimethyl-N-oxymethylpyrazolato-N2,µ3-O)(ethanol)nickel(II)]

The synthesis, and spectroscopic and magnetic characterisation of four isomorphous cluster compounds of general formula [{MX(L)(EtOH)}4][L = 3,5-dimethyl-1-oxymethylpyrazolate(1–); X = Cl or Br; M = CoII or NiII] is described. The compounds are formed upon reaction of 1-(hydroxymethyl)-3,5-dimethylpyrazole (HL) with the metal(II) halides in ethanol in the presence of one equivalent of KOH. The deprotonated ligand co-ordinates as a bidentate ligand through its pyrazole N2 nitrogen and the oxy-part. The oxygen atom bridges between three metal ions, thereby forming a M4O4 cubane-type cluster. In the case of M = Ni the metal ions are ferromagnetically coupled, whereas in the case of M = Co antiferromagnetic coupling occurs. The presence of the cubane-type structure was confirmed by the crystal structure determination of [{NiCl(L)(EtOH)}4]. The complex crystallizes in space group P21/n with a= 12.936(6), b= 18.152(5), c= 20.79(1)A, β= 106.23°, and Z= 4. Standard least-squares refinement gave R= 0.039 (R′= 0.047). The Ni atom has a NiO4NCl chromophore in a distorted octahedral geometry. Important averaged distances are: Ni–N = 2.06, Ni–Cl = 2.35, Ni–O(EtOH)= 2.08, Ni–O = 2.08 and, Ni ⋯ Ni = 3.18 A. Intramolecular hydrogen bonds between Cl (bound to one Ni) and EtOH (bound to another Ni) with average O ⋯ Cl contacts of 3.01 A stabilize the cluster.

Synthesis, crystal structure and properties of two acetazolamide (5-acetamido-1,3,4-thiadiazole-2-sulfonamide) complexes: bis(5-acetamidato- 1,3,4-thiadiazole-2-sulfonamide-O)bis( 1,2-ethanediamine)copper(II) and bis(5-acetamidato-1,3,4-thiadiazole-2-sulfonamide-N)bis(1,3- propanediamine)copper(II); an unusually weak ambidentate anionic ligand

Abstract The diverse coordination chemistry exhibited by acetazolamide (H2acm), a potent inhibitor of the carbonic anhydrase metalloenzyme, is highlighted in two new copper(II) complexes of this ligand: [Cu(Hacm)2(en)2] (I) and [Cu(Hacm)2(tn)2] (II). The synthesis, crystal structure and spectroscopic properties of both compounds are reported in this paper. The structures of both compounds consist of discrete units of [Cu(Hacm)2(en)2] (I) and [Cu(Hacm)2(tn)2] (II), respectively, interacting through van der Waals contacts and hydrogen bonds only. Hacm, however, binds differently in each compound. In both cases, the Cu(II) ions, lying on the symmetry centers, show an elongated octahedral geometry with the four 1,2-ethanediamine or 1,3-propanediamine N atoms in an approximately square coplanar arrangement (Cu-N distances of 2.00 and 2.01 A for I; 2.04 and 2.05 A for II); two sulfonamido O atoms in I and two thiadiazole N atoms in II, from two trans Hacm ligands, complete the distorted octahedron at the longer distance of 2.65 and 2.46 A, respectively. Although the ligand is deprotonated at the acetamido group, in neither case is the interaction with the copper produced via the donor atoms of that group. Furthermore, in I, unexpectedly, in spite of its four potentially chelating N atoms, and in spite of the deprotonation of the acetamido group, acetazolamide acts as a monodentate ligand coordinating through one of the O atoms of the sulfonamido moiety. This behavior is completely different from that observed in II and in all acetazolamide complexes described up to now, and it must be related to hydrogen bonding and to the copper(II) Jahn-Teller effect. Stabilization of the negative charge at the deprotonated group takes place through ‘pairing’ of the Hacm ions in the packing system. These results further emphasize the many coordinating possibilities of the ligand, which could be of relevance to a proper understanding of the mechanism of inhibition in the enzyme. Crystallographic data: [Cu(C4N4S2O3H5)2(C2N2H8)2] (I) (MW=626.2) crystallizes in the triclinic space group P 1 , Z=1, with the cell dimensions a=8.196(7), b=9.094(4), c=9.352(3) A, α=84.51(3), β=74.83(6), γ=63.57(5)° and V=602 A3, Dcalc=1.73 Mg m−3; the final agreement values were R=0.0335 and Rw=0.0427 for 3947 independent significant reflections. [Cu(C4N4S2O3H5)2(C3N2H10)2] (II) (MW=654.3) crystallizes in the monoclinic space group P21/n, Z=2, with the cell dimensions a=9.336(3), b=10.232(1), c=14.138(3) A, β=103.80(2) and V=1312 A3, Dcalc=1.66 Mg m−3; the final agreement values were R=0.0327 and Rw=0.0405 for 1932 independent significant reflections. The structures were solved by using the copper coordinates (at the inversion center) for repeated Fourier calculations (AUTOFOUR, SHELXS-86). Ligand field and EPR spectra for both complexes are in agreement with the tetragonal Cu(II)N4O2 (I) and Cu(II)N4N2′ (II) chromophores, respectively.

Dalton communications. The first dinuclear µ-hexafluorosilicato copper(II) compound. Synthesis and crystal structure of (µ-hexafluorosilicato-κF:κF′)-bis[aqua(N3-salicyloylpyridine-2-carboxamidrazonato-κ3N′,N2,O)copper(II)] dihydrate

The X-ray structure of a unique dinuclear copper(II) compound containing a single hexafluorosilicato bridge, [Cu2L2(H2O)2(SiF6)]·2H2O (HL =N3-salicyloylpyridine-2-carboxamidrazone), is reported.

A novel type of tetranuclear copper(II) cluster, containing deprotonated 3-(pyridin-2-yl)-5-(pyrazin-2-yl)-1,2,4-triazole (Hppt) as a diatomic bridging ligand. Preparation, magnetism, and X-ray crystal structure of [Cu(µ-ppt)(H2O)]4(NO3)4(H2O)12

The title compound, characterized by means of an X-ray structure analysis, represents the first example of a tetranuclear co-ordination compound with only diatomic bridges.