J. Reedijk

Influence of alkyl chain length in N-alkyl imidazoles upon the complex formation with transition-metal salts

Abstract Preparation and properties of a large number of compounds with the general formula M(NRIz)n(anion)2 are described; in this formula M  Mn, Co, Ni, Zn, Cd; n = 1,2,3,4 and 6; NRIz stands for N-alkyl imidazole ligands (alkyl = Me, Et, Pr, Bu); the anions are ClO4−, BF4−, NO3−, Br− and Cl−. The compounds are characterized with the aid of far-IR ligand-field and ESR spectra and X-ray powder diagrams. The stoichiometry of the compounds depends upon the particular cation and anion, but also on the length of the alkyl substituent. This effect appears more pronounced in the m.ps of classes of similar compounds. Generally the m.ps follow three lines: 1. (a) cations: the Irving-Williams sequence is found; 2. (b) the anions occur in a sequence according to the ionic size; the larger the anion, the higher the m.p.; 3. (c) the ligands produce a sequence which follows the ligand size, i.e. the larger the substituent, the lower the m.p. Similar sequences are found in ligand-field and ESR spectra. Only in a few cases deviations from these lines occur in the sequence of stoichiometry, m.ps and spectral data. This may be due to different structures, probably caused by steric effects of the ligands.

Coordination compounds of Pt(II) and Pd(II) with imidazole as a ligand. New synthetic procedures and characterization

Abstract The synthesis and characterization of a number of new coordination compounds of Pt(II) and Pd(II) with the nitrogen-donor ligand imidazole (IzH) is described. These compounds are cis-Pt(IzH)2X2 trans-Pt(IzH)2X2, Pt(IzH)4X2, trans Pd(IzH)2X2, Pd(IzH)4X2 where X = Cl, Br or I and Pt(IzH)4PtX4, Pd(IzH)4PdX4, where X = Cl or Br, and cis-Pd- (IzH)2X2 where X = Cl, Br or X2 = C2O4, as well as Pt(IzH)2(Iz)2 and Pd(Iz)2 where Iz is the imidazolato anion. The new compounds are characterized by chemical analyses, X-ray powder diffraction photographs, vibrational spectroscopy (infrared- and far- infrared spectroscopy) and proton nuclear magnetic resonance. The metal(II) ions are in all cases coordinated in a square-planar geometry. In Pd(Iz)2 a polymeric structure exists with bidentate, bridging imidazolato anions.

Spectral Properties and Crystal Structure of Bis(μ-thiocyanato-N,S)bis(thiocyanato-N)-tetrakis(5,7-dimethyl[1,2,4]triazolo[1,5-α]pyrimidine-N3)dicopper(II) and of Tetrakis(5,7-dimethyl[1,2,4]triazolo[1,5-α]pyrimidine-N3)platinum(II)hexa(thiocyanato-S)platinate(IV).

Abstract The preparation, spectroscopic studies and the crystal structure of Cu(dmtp) 2 (NCS) 2 ( I ) and Pt(dmtp) 4 Pt(SCN) 6 ( II ) (dmtp stands for the 5,7-dimethyl[1,2,4]triazolo[1,5- a ] pyrimidine ligand) are described. Crystals of I are monoclinic, space group C 2/ c , with a = 19.088(7), b = 11.516(8), c = 20.118(7) A, β = 104.51(4)°, Z = 28; crystals of II are monoclinic, space group P 2 1 / n , with a = 16.914(8), b = 11.474(9), c = 11.893(7) A, β = 91.52(4)°, Z = 2. The structures of I and II have been solved from diffractometer data by Patterson and Fourier methods and refined by full-matrix least-squares to R = 0.044 for I and 0.051 for II . The structure of I consists of centrosymmetric dimers [Cu(dmtp) 2 (NCS) 2 ] 2 , in which the copper atoms, bridged by two thiocyanate groups, are in a square pyramidal arrangement involving two isothiocyanate nitrogen atoms and two triazole nitrogen atoms from two dmtp ligands in the basal plane and a thiocyanate sulphur atom from the centrosymmetric complex in the apical position. The structure of II consists of square planar [Pt(dmtp) 2 ] 2+ cations, in which the platinum atom is bound to four triazole nitrogen atoms from dmtp ligands and of octahedral [Pt(SCN) 6 ] 2− anions with the metal bound to sulphur atoms of thiocyanate anions.

The interactions of cis- and trans-diammineplatinum compounds with 5′-guanosine monophosphate and 5′-deoxyguanosine monophosphate. A proton nmr investigation

Abstract The interactions of cis - and trans -diammineplatinum compounds with 5′-GMP and 5′-dGMP in dilute aqueous solution at neutral pH were investigated by 1 H nmr. In addition to the 1:2 Pt nucleotide complexes cis - and trans -Pt(NH 3 ) 2 (GMP) 2 , it was possible to study the formation of the 1:1 Pt-nucleotide complexes with either one coordinated water or chloride ion. At 5°C GMP reacts with a stoichiometric amount of cis -diaquodiammine-platinum to yield cis -Pt(NH 3 ) 2 (GMP) (H 2 O) as a sole reaction product. From the present results it is concluded that such a complex may play an important role as the initial reaction product between antitumor compounds like cis -Pt(NH 3 ) 2 Cl 2 and guanine in DNA in living organisms. The coupling constant 3 J(H(1′)-H(2′)) of the H(1′) sugar proton in cis -Pt(NH 3 ) 2 (GMP) 2 is temperature dependent, indicating a conformational change in the sugar moiety.

Linear trinuclear coordination compounds with 4-ethyl-1,2,4-triazole. Structure and magnetic properties

Abstract The synthesis and characterisation of a series of linear trinuclear coordination compounds containing 4-ethyl-1,2,4-triazole (Ettrz) are presented. The crystal structure of the first linear trinuclear Mn(II) compound [Mn 3 (Ettrz) 6 (H 2 O 6 ](CF 3 SO 3 ) 6 was determined at room temperature. The compound crystallizes in the space group P 3 1 c , with lattice constants a = b = 14.545(2) A and c = 20.072(3) A. In the linear trimer the metal ions are linked by three 1,2-bidentate coordinating triazole ligands. The manganese ions are coordinated octahedrally. For the terminal metal ions the octahedral coordination is completed by H 2 O molecules. The coordination distances are: MnN 2.24 A and MnO 2.19 A. The Co(II), Ni(II) and Zn(II) compounds are X-ray isomorphous with the Mn(II) compound. The magnetic exchange in the Mn, Co and Ni compounds is antiferromagnetic with J values of −0.6 cm −1 , −14.7 cm −1 (Ising approximation) and −9.4 cm −1 , respectively. An expression for the magnetisation and magnetic susceptibility of a linear Mn(II) trimer is presented. The Cu(II) and Cd(II) compounds, with composition [M 3 (Ettrz) 9 (H 2 O) 3 ](CF 3 SO 3 ) 6 (H 2 O) x , are also likely to be trinuclear. The terminal coordination sites in these compounds appear to be occupied by three monodentate coordinating triazole ligands and three water molecules. Surprisingly, the magnetic exchange in the Cu compound appears to be ferromagnetic.

Coordination compounds of benzotriazole and related ligands

Abstract The coordination chemistry of benzotriazole towards several transition metal compounds has been studied. Unpon reaction of neutral benzotriazole (BTAH) with metal compounds under varying conditions, both neutral (BTAH) ligands and anionic, deprotonated ligands (BTA − ) may be coordinated to the metal. The compounds have the general formula M(BTAH) n X m , with M = Cu, Zn, Cd, Hg, Pd, Ti, Sn, n = 1, 2, 3, 4, X = Cl, Br and m = 2 or 4. Similar compounds of formula Cu(ligand) n X 2 (X = Cl, Br; n = 1, 2) with 5-nitrobenzotriazole and N-methylbenzotriazole, were obtained. Compounds with anionic BTA have the formulae: Cu(BTA)Cl, Cu(BTA) 1.5 (BF 4 ) 0.5 , Cu(BTA) 2 , Hg(BTA) 2 , Cu(phen) 2 (BTA) 2 , Hg(BTA)(CH 3 ), Si(BTA)(CH 3 ) 3 , Mn(BTA)(CO) 5 . In addition some mixed compounds were isolated, i.e. Cu 2 (BTA) 2 (BTAH)(NO 3 ) 2 , Cu 2 (BTA)(BTAH)(SO 4 ) and Ni(BTAH)(BTA)(BF 4 ). Structures of the compounds have been proposed based on infrared and far-infrared spectroscopy, ligand field and UV spectroscopy, EPR spectroscopy, conductivity data and NMR spectroscopy. The most common mode of bonding for neutral, monodentate benzotriazole to metal ions seems to involve N(3) in BTAH (this is named N(1) in BTA). In the case of bidentate binding, it is not clear whether N(1)N(2) or N(1)N(3) bidentate bridging occurs. Spectral measurements are unable to distinguish between these modes. Tridentate binding of salt-like structures seems likely for Cu(BTA) 2 and Hg(BTA) 2 , and might be present in a few other compounds such as Cu(BTA)Cl. Due to the insoluble nature of most of the compounds, polymeric structures using BTA and BTAH as bridging ligands seem to occur most frequently. Such structures are discussed in relation to the corrosion-inhibiting properties of benzotriazole.

Coordination compounds of Pt(II) with N-methyl imidazole as a ligand

Abstract The synthesis of a number of new coordination compounds of Pt(II) with the nitrogen-donor ligand N-methyl imidazole (NMIz) is described. These compounds are cis-Pt(NMIz)2X2, Pt(NMIz)2C2O4·H2O, trans-Pt(NMIz)2X2, Pt(NMIz)4X2(H2O)n and Pt(NMIz)4PtX4 where X = Cl, Br or 1 and n = 0 or 2, and the mixed-valence compound Pt[NMlz)4PtCl6. The new compounds are characterised by chemical analyses, X-ray powder diffraction, vibrational spectroscopy (infrared, far-infrared and Raman spectroscopy), thermal analyses (thermogravimetry and differential thermal analysis) and proton nuclear magnetic resonance. The cis-dichloro and cis-dibromo compounds exist in several crystal forms with slightly different spectroscopic properties. When dissolved in concentrated hydrochloric acid and exposed to air, the compound Pt(NMlz)4PtCl4 is axidised to Pt(NMIz)4PtCl6.

Transition-metal(II) thiocyanate coordination compounds with 4-t-butyl-1,2,4-triazole. Structure and magnetic properties

Abstract The synthesis, spectroscopy and structure of a series of t-Butrz coordination compounds with varying geometries is described. [Zn(t-Butrz)2-(NCS)2] is a mononuclear compounds, in which the Zn(II) ion is coordinated tetrahedrally. [Mn2(t-Butrz)4(H2O)(NCS)4] and its Fe(II) analogue are both asymmetrical dinuclear compounds. In the manganese compounds a small antiferromagnetic exchange (J - 0.5 cm−1 is present. the crystal structure of [Co3(t-Butrz)8(NCS)4]-(NCS)2(H2O)9 was determined at room temperature. It crystallizes in the space group P21/n, with lattice constants a = 15.616(3) », b = 14.168(4) », c = 19.517(7) », and β = 90.48(2)°. The unit cell contains two trinuclear units. In the linear trimer the Co centers are linked by three 1,2-bicoordinating t-Butrz groups (CoCo: 3.88 »). The central Co(II) ion is therefore coordinated by 6 t-Butrz ligands. For the terminal Co ions the octahedral coordination is completed by two N-donating thiocyanate anions (CoN: 2.10 ») and a monodentate coordinating t-Butrz (CoN: 2.13 »). The non-coordinating nitrogen atom of this triazole ligands is involved in hydrogen bonding (ON: 2.98 »). The magnetic properties of this compound can be described in terms of a S = 1 2 formalism. Application of the Ising model yields J = −13.2 cm−1 and g = 7.8. The magnetic interaction in the corresponding isostructural Ni compound is antiferromagnetic also (J = 10.0 cm−1, g = 2.02). [Co3(t-Butrz)4(NCS)6](H2O)2 is a trinuclear compound in which the central Co(II) ion is coordinated octahedrally, while the terminal Co ions reside in tetrahedral coordination sites. Attempts to replace the terminal Co ions by Zn(II) ions appeared to be successful. The magnetic exchanged in [Cu(t-Butrz)2(NCS)2](H2O)0.5 is antiferromagnetic and unusually strong. Based on spectral data a layer structure is proposed for this compound. Cd(t-Butrz)1.5(NCS)2 is a linear-chain type compound, containing alternating units of bridging ligands and unusual bridging NCS anions.

Linear-chain anti-ferromagnetism and spectroscopy of compounds CuX2L2, with x = CI, Br and L = substituted pyridine

Abstract A series of linear-chain systems CuX2L2, with X= Cl, Br and L = substituted pyridine, is prepared and investigated. I.R., far-I.R., ligand-field and ESR spectra have been recorded; furthermore, magnetic susceptibility data at low temperatures are collected in order to find out the influence of small changes in the ligand molecule on the exchange constants. The chloride and bromide compounds of each ligand appear to be isomorphous according to the I.R. spectra, although small differences in the X-ray diffraction patterns occur. The M-X and M-L frequencies, which occur in the far-infrared region, have been assigned. The ESR parameters differ only slightly for the several chloride compounds, although the g-value of the 4-Etpy compound is less anisotropic than that of the others. All bromides have nearly the same ESR spectra. The susceptibility data of the compounds have been collected over the temperature region 4.2–80.0 K. J values for the compounds are calculated using the Heisenberg model for one-dimensional systems. The data do not agree with the Ising model. All compounds behave like antiferromagnetically-coupled copper ions bridged by halogen atoms. The J values correlate with a Cu-X frequency in the far-infrared. Examination of the exchange coupling constants reveals that the J values for the bromide compounds are consistently higher than those of the corresponding chlorides. Structural data show that the magnitude of exchange is influenced by the steric effects of the different ligands. For complete understanding of the factors influencing exchange coupling in these linear-chain systems, more detailed structural data are needed.

Transition-metal(II) thiocyanate coordination compounds containing 4-allyl-1,2,4-triazole. Structure and magnetic properties.

The synthesis and characterisation of a series of dinuclear and polynuclear coordination compounds with 4-allyl-1,2,4-triazole are described. Dinuclear compounds were obtained for Mn(II) and Fe(II) with composition [M2(Altrz)5(NCS)4], and for Co(II) and Ni(II) with composition [M2(Altrz)4(H2O)(NCS)4](H2O)2. The crystal structure of [Co2(Altrz)4(H2O)(NCS)4](H2O)2 was solved at room temperature. It crystallizes in the monoclinic space group P21/n. The lattice constants are a = 18.033(3) A, b = 13.611(2) A, c = 15.619(3) A, β = 92.04(2)° Z = 4. One cobalt ion has an octahedrally arranged donor set of ligands consisting of three vicinal nitrogens of 1,2-bridging triazoles (CoN = 2.14–2.15 A), one terminal triazole nitrogen (CoN = 2.12 A) and two N-bonded NCS anions (CON = 2.08 A). The other Co(II) ion has the same geometry, but the terminal triazole ligand is replaced by H2O (CoO = 2.15 A). The crystal structure is stabilised by hydrogen bonding through H2O molecules, S-atoms of the NCS anions and the lone-pair electron of the monodentate triazole. The magnetic exchange in the Mn, Co and Ni compounds is antiferromagnetic with J-values of −0.4 cm−1, −10.9 cm−1 and −8.7 cm−1 respectively. The Co compound was interpreted in terms of an Ising model. For [Zn2(Altrz)5(NCS)2]∞[Zn(NCS)4], [Cu2(Altrz)3(NCS)4]∞ and [Cd2(Altrz)3(NCS)4]∞ chain structures are proposed. In the Cu compound thiocyanates appear to be present, bridging via the nitrogen atom, as deduced from the IR spectrum.