Gerard A. van Albada

The first structural evidence of a polymeric Cu(II) compound with a bridging dicyanamide anion: X-ray structure, spectroscopy and magnetism of catena-[polybis(2-aminopyrimidine)copper(II)bis(μ-dicyanamido)]

Abstract The new Cu(II) coordination compound, catena-[Cu(N(CN)2)2(ampym)2] (in which ampym=2-aminopyrimidine) has been synthesized and investigated by X-ray analysis, ligand field, EPR spectroscopy and magnetic susceptibility. The first compound crystallizes in the monoclinic space group C2/c with a=13.579(6), b=15.453(5), c=7.570(7) A, β=92.03(5)° and refines to an R value of 0.0322. The geometry around the copper(II) atom is axially elongated octahedral with the basal plane formed by the nitrogen of two monodentate coordinating ligands and two (N2) nitrogens of the bridging dicyanamide anions with distances which vary from 1.972(3) to 2.078 A forming an almost perfect square planar geometry. The apical positions are occupied by the other nitrogens (N3) of the bridging dicyanamide anions with a distance of 2.416(3) A. The bridging dicyanamide forms a one-dimensional polymeric chain with the other copper units. The CuCu separation is 7.570 A. Hydrogen bonding (3.1231 A) between the hydrogen atoms of the amino nitrogen and the uncoordinated nitrogen of the ligand forming pairs of ligands stabilizes the lattice, and bridges the chain in 2D-sheets. A Ligand field maximum occurs at 14.3×103 cm−1 and the EPR values, measured as a solid, are g⊥=2.08 and g//=2.29. Magnetic susceptibility of the powdered sample was measured from 4 to 300 K. The inverse susceptibility versus temperature shows that the curve follows the Curie–Weiss law. The μeff versus temperature gives a negligible rise at lower temperature and stays constant at about 1.80–1.84. The characteristic infrared vibrations for the dicyanamide anion are the νs+νas(CN), found as one strong band at 2301 cm−1, and the ν (C  N) , found as two strong bands at 2254 and 2188 cm−1.

Two Examples of Novel and Unusual Double-Layered, Two-Dimensional CuII Compounds with Bridging 1,3-Bis(1,2,4-triazol-1-yl)propane

The synthesis and characterisation of two new polymeric CuII complexes is described, i.e. {[Cu(btp)2(CH3CN)(H2O)](CF3SO3)2}n (1) and {[Cu(btp)2(CH3CN)2](ClO4)2}n (2), in which btp = [1,3-bis(1,2,4-triazol-1-yl)propane]. Compound 1 crystallizes in space group P21/c with a = 11.9337(15) A, b = 20.108(6) A, c = 12.748(6) A, β = 92.247(14)°, and Z = 4. Compound 2 crystallizes in space group Pna21 with a = 18.770(8) A, b = 12.648(8) A, and c = 12.019(8) A. The structures refined to R1 values of 0.0683 for 1 and 0.0846 for 2. In both structures the CuII ions are linked by the bridging ligands, resulting in two-dimensional networks. Two such curved layers are arranged on top of each other with center-to-center of layer distances of 2.12 A in 1 and 1.98 A in 2. Such double layers are separated from each other by 10.05 A in 1 and 9.385 A in 2. The space between the double layers is occupied with interstitial anions. No significant interaction between CuII ions is observed by EPR and magnetic susceptibility measurements. The compounds form a new class of a lattice engineered system held together by the CuII ions. – The coordination geometry of the copper ions is distorted octahedral, with the equatorial plane formed by the N4 nitrogens of the four triazole groups and the axial sites occupied by solvent molecules; acetonitrile and water in structure 1 and two acetonitrile molecules in structure 2. The two structures are related by a group–subgroup relationship, which appears to be the first such case in supramolecular chemistry. – The Cu–N vibrations in the FIR region are found at 274 cm–1 for 1, and at 276 cm–1 for 2. The ligand-field maxima are observed at about 16·103 cm–1, with a shoulder at about 12·103 cm–1. The νCN stretching vibrations of the acetonitrile molecules are found at 2303 and 2261 cm–1 for 1, and at 2313, 2294, 2278, and 2260 cm–1 for 2.

Synthesis, spectroscopic properties and X-ray crystal structures of two dinuclear alkoxo-bridged copper(II) compounds with the ligand bis(1-methyl-2-benzimidazolyl) propane. A unique alkoxo-bridged Cu(II) dinuclear compound with an additional bidentate bridging triflate anion

Abstract Based on the new ligand bis(1-methyl-2-benzimidazolyl) propane (abbreviated as mtbz) several new copper(II) coordination compounds have been prepared and characterized structurally and spectroscopically. Two representative compounds, i.e. [Cu 2 (mtbz) 2 (CH 3 ) 2 - (CF 3 SO 3 )](CF 3 SO 3 ) ( 1 ) and [Cu 2 (mtbz) 2 (CH 3 O) 2 ](ClO 4 ) 2 ( 4 ) were characterized structurally by X-ray diffraction. Crystal data for 1 : monoclinic, space group P 2 1 / c , a=13.6585(5), b=39.981(3), c=20.919(1) A , β=125.98(1)°, Z=8 . Crystal data for 4 : monoclinic, space group P 2 1 / c , a=13.115(2), b=9.523(2), c=17.908(4) A , β=111.71(1)°, Z=2 . Structures 1 and 4 each consist of a dinuclear unit with bridging methoxo groups and one ligand linked to each copper via an N atom. Structure 1 (which consists of two dinuclear, crystallographically independent, but chemically identical units) has the two copper atoms bridged by a triflate anion, providing each copper atom a square-pyramidal coordination, while the copper atoms in structure 4 have an almost a square-planar geometry. The CuCu distances (A) within the dinuclear units are: 1 , 2.9775(13), 2.9751(13); 4 , 2.9872(16); the CuOCu bridging angles (°) are: 1 , 101.7(3), 101.7(3), 100.9(3), 102.1(3); 4 , 103.2(2). The mid-IR section focused on the vibrations of the triflate anion reveals interesting results concerning the assignments of that anion related to the v as (SO) band. Characteristic CuO vibrations in the far-IR section were found at 386 and 230 cm −1 for the methoxo-bridged and 454 and 332 cm −1 for the ethoxo-bridged compounds. These dinuclear species are EPR silent, and only a weak signal of monomeric impurities is observed. They also show a diamagnetic behavior below room temperature.

Increase in coordination number of lanthanide complexes with 2,2′-bipyridine and 1,10-phenanthroline by using β-diketonates with electron-withdrawing groups

Abstract The coordination chemistry of Ln(hfpd)3 (hfpd=1,1,1,5,5,5-hexafluoropentane-2,4-dionate) with phen and bpy depends on the size of the Ln3+ ion and on the used solvent. The complexes [Er(hfpd)3(phen)] (7) and [Er(hfpd)3(bpy)] (14) were obtained from the synthesis of Er(CF3SO3)3 with Hhfpd, CsOH and either 1,10-phenanthroline or 2,2′-bipyridine in acetonitrile. The structure of 7 was determined by X-ray crystallography. Similar reactions, but performed in methanol, with various other lanthanide elements resulted in isolation of five different types of complexes, according to stoichiometry and spectral properties. With elements later in the lanthanide series eight-coordinated complexes of the types [Ln(hfpd)3(bpy)] (for Ln=Dy, Ho and Yb) and [Ln(hfpd)3(phen)] (for Ln=Tb, Ho and Yb), like 7, were obtained, whereas with the early lanthanide elements ten-coordinated complexes of the types [Ln(hfpd)3(bpy)2] (for Ln=La and Sm) and [Ln(hfpd)3(phen)2] (for Ln=La, Ce, Pr and Nd) were isolated. The X-ray crystal structure of [La(hfpd)3(bpy)2] (9) was determined, which provided proof for ten-coordination around the La ion. In addition to [Sm(hfpd)3(bpy)2], the synthesis with Sm and bpy and a trace of water yielded a second compound: the nine-coordinated complex [Sm(hfpd)3(H2O)(bpy)]·(bpy) (11), which was structurally characterised by X-ray crystallography. The LnN distances vary largely, depending on the used N-donor and the Ln3+ ion, and do not run parallel with the Ln3+ ionic radius.

Two-Step Spin-Transition Iron(III) Compound with a Wide [High Spin-Low Spin] Plateau

A new iron(III) coordination compound exhibiting a two-step spin-transition behavior with a remarkably wide [HS-LS] plateau of about 45 K has been synthesized from a hydrazino Schiff-base ligand with an N,N,O donor set, namely 2-methoxy-6-(pyridine-2-ylhydrazonomethyl)phenol (Hmph). The single-crystal X-ray structure of the coordination compound {[Fe(mph)(2)](ClO(4))(MeOH)(0.5)(H(2)O)(0.5)}(2) (1) determined at 150 K reveals the presence of two slightly different iron(III) centers in pseudo-octahedral environments generated by two deprotonated tridentate mph ligands. The presence of hydrogen bonding interactions, instigated by the well-designed ligand, may justify the occurrence of the abrupt transitions. 1 has been characterized by temperature-dependent magnetic susceptibility measurements, EPR spectroscopy, differential scanning calorimetry, and (57)Fe Mossbauer spectroscopy, which all confirm the occurrence of a two-step transition. In addition, the iron(III) species in the high-spin state has been trapped and characterized by rapid cooling EPR studies.

The binding mode of the ambidentate ligand dicyanamide to transition metal ions can be tuned by bisimidazoline ligands with H-bonding donor property at the rear side of the ligand

The synthesis and crystal structures, as well as the electronic and magnetic properties, of four new compounds containing the ligands 2,2′-biimidazoline (biz) and dicyanamide (dca) with the general formula M(II)(biz)x(dca)2 (where M = Cu(II), Co(II), Ni(II) and x = 1,2) are reported. In the compound Cu(biz)(dca)2(1), the equatorial plane around the Cu(II) atom is formed by two nitrogen atoms of one biz ligand and two nitrile atoms of two dca molecules. The dca anions are connected to a neighbouring Cu atom, with the central amide nitrogen acting as the axial atom, forming in this way a 2D polymeric sheet. The compounds Cu(biz)2(dca)2 (2) and Co(biz)2(dca)2 (3), which are isostructural, contain octahedral metal ions with the basal plane occupied by four nitrogen atoms of two biz ligands and the axial positions formed by two amide nitrogen atoms of monodentate dca ligands. The compound Ni(biz)2(dca)2 (4), differs from 2 and 3, as in this case the axial positions are occupied by the nitrile nitrogen atoms of a monodentate dca ligand. The main difference between the Co and the Cu compounds is the axial M–N bond, which in the case of Cu is elongated to 2.60 A, due to the Jahn–Teller effect. The coordination of the metal atom via the amide nitrogen atoms of dca has so far rarely been observed. All four compounds also show quite different hydrogen bonding systems via the N–H groups of the biz ligands and the nitrile nitrogen atoms of the dca molecules, forming interesting 3D and 2D polymeric and sheet-like arrays. The infrared absorptions of the compounds, as well as the electronic and EPR absorptions, are in good agreement with the crystal structures obtained. Magnetic susceptibility measurements revealed that no significant (J > −1 cm−1) interactions are present between the metal atoms, as was expected, since no serious overlap of the magnetic metal orbitals takes place via the dca ligands.

Ferromagnetic trinuclear carbonato-bridged and tetranuclear hydroxo-bridged Cu(II) compounds with 4,4′-dimethyl-2,2′-bipyridine as ligand. X-ray structure, spectroscopy and magnetism

Abstract A controlled synthesis, characterisation and single-crystal X-ray analysis of two novel copper(II) compounds with the ligand 4,4′-dimethyl-2,2′-bipyridine (abbreviated dmbipy) is described. In a CO2 atmosphere, with sodium hydroxide added, the carbonato-bridged triangular trinuclear compound [Cu3(dmbipy)6(μ3-CO3)](BF4)4(C2H5OH)(H2O) (1) is obtained. Compound 1 crystallises in the monoclinic space group P21/n with a=16.169(6), b=23.351(11), c=21.312(7) A, β=91.26(3), Z=4. The three copper ions are connected via the oxygen atoms from the symmetrically bridging carbonato group, resulting in a triangular array of copper atoms. Each copper has a distorted square-pyramidal environment with a basal plane formed by three nitrogen atoms of the two chelating bipyridine groups and the oxygen atom of the bridging carbonato group (Cu–N/O distances about 2.0 A). The apical position at each copper is occupied by the fourth nitrogen atom of the bipyridines with distances varying from 2.100(11) to 2.146(11) A. In all other experimental conditions the tetranuclear hydroxo-bridged compound [Cu4(dmbipy)4(μ3-OH)2(μ-OH)2(H2O)2](BF4)4(H2O)4 (2) is obtained. Compound 2 crystallises in the monoclinic space group P21/c with a=13.274(8), b=21.685(7), c=11.266(7) A, β=107.71(4), Z=2. The structure consists of two bis(hydroxo)-bridged dinuclear planar units which are connected with long Cu–O bonds to form a tetranuclear unit. Each Cu ion has a similar square-pyramidal coordination geometry: the equatorial plane of each Cu ion consists of two nitrogen atoms of the dmbipy ligand (Cu–N distances 1.945–2.003 A), and two bridging hydroxo oxygen atoms (Cu–O distances 1.945–1.973 A). The apical position of Cu1 is occupied by an oxygen atom of a water molecule with a distance of 2.262 A. The second copper atom, Cu2, has the apical position occupied by an oxygen atom of a bridging hydroxo group at a distance of 2.349 A; this bond is responsible for the formation of the tetranuclear unity. Compound 1 exhibits a ferromagnetic interaction between the copper ions with a J=29.3 cm−1 and a very weak ferromagnetic intercluster interaction with zj′=2.4 cm−1. Compound 2 also exhibits a ferromagnetic interaction between the copper ions with a J=31.1 cm−1 and an overall magnetic interaction between the two dimeric units J′=8.76 cm−1

Synthesis, spectroscopic characterization, X-ray crystal structure and magnetic properties of oxalato-bridged copper(II) dinuclear complexes with di-2-pyridylamine

The syntheses and characterization of a series of dinuclear μ-oxalato copper(II) complexes of the general type [(NN) 1 or 2 Cu(C 2 O 4 )Cu(NN) 1 or 2 ] 2+ , where NN=didentate dpyam (di-2-pyridylamine) ligand, are described. The crystal structures of three representative complexes have been determined. The dinuclear-oxalate bridged compounds [Cu(dpyam) 4 (C 2 O 4 )](ClO 4 ) 2 (H 2 O) 3 (1) and [Cu 2 (dpyam) 4 (C 2 O 4 )](BF 4 ) 2 (H 2 O) 3 (2) crystallize in the non-centrosymmetric triclinic space group P which are isomorphous and isostructural. The compound [Cu 2 (dpyam) 2 (C 2 O 4 )(NO 3 ) 2 ((CH 3 ) 2 SO) 2 ] (3) crystallizes in the centrosymmetric monoclinic space group P with all Cu-oxalate contacts in the equatorial plane. All three complexes contain six-coordinate copper centres bridged by planar bis-didentate oxalate groups from the equatorial position of one chromophore to the equatorial position of the other one. Both chromophores in 1 and 2 exhibit the compressed octahedral Cu(II) geometry, while 3 displays an elongated octahedral Cu(II) environment. The IR, ligand field and EPR measurements are in agreement with the structures found. The magnetic susceptibility measurements, measured from 5 to 280 K, revealed a very weak ferromagnetic interaction between the Cu(II) atoms for compound 1 and 2 , with a singlet–triplet energy gap ( J ) of 2.42 and 3.38 cm −1 , for compounds 1 and 2 , respectively. Compound 3 has a strong antiferromagnetic interaction with a J of −305.1 cm −1 , in agreement with coplanarity of the magnetic orbitals.

Alkoxo-bridged dinuclear copper(II) compounds with 2-amino-picolines as ligands: Synthesis, spectroscopy, magnetism and X-ray crystal structures

Abstract The synthesis, spectroscopic, magnetic and structural characterisation of four new alkoxo-bridged dinuclear copper(II) compounds are described. All four compounds have the general formula [Cu(μ-OR−)(L)2]2(A−)2, in which μ-OR=CH3O− or CH3CH2O−, L=2-amino-3-picoline (abbreviated as 3pic) and 2-amino-5-picoline (abbreviated as 5pic) and A=NO3− or ClO4−. The title compounds all consist of dinuclear units with bridging methoxo groups for [Cu(3pic)2(CH3O)2(NO3)2](CH3OH)2 (1), [Cu(3pic)2(CH3O)2(ClO4)2](CH3OH)2 (2), Cu(5pic)2(CH3O)2(ClO4)2 (3) and a bridging ethoxo group for Cu(5pic)2(C2H5O)2(ClO4)2 (4) with two picoline ligands linked to each copper via the pyridine N atom, providing a square planar CuN2O2 unit. The nitrate anions in compound (1) are bridging at semi-coordination distance (Cu–ONO3 2.735–2.793 A), the perchlorate anions in compounds (2) and (3) are at semi-coordination distance (Cu–OClO4 2.701–3.042 A); on the other hand the perchlorate anion in compound (4) has only one semi-coordination bond (Cu–OClO4 2.826 A). The Cu–Cu distances within the dinuclear units are 2.9957(12), 2.9872(15), 2.996(5), and 3.0123(18) A for compounds (1), (2), (3) and (4), respectively, with Cu–O–Cu angles of 102.3(8), 101.33(13), 103.8(5), and 103.38(16)° for compounds (1), (2), (3) and (4), respectively. The structures are stabilized by intramolecular H-bonds between the amino hydrogens and Omethoxo and/or Oanion atoms (shortest contacts N–H⋯Omethoxo 3.108 A; N–H⋯Oanion 2.914 A). The magnetic susceptibility measurements of the alkoxo-bridged compounds display a diamagnetic behaviour below room temperature with an estimated exchange parameter 2J of

Synthesis, magnetism and X-ray structures of [Cu(2-aminopyrimidine)2(μ-OH)(CF3SO3)]2(2-aminopyrimidine)2, a new hydroxo-bridged dinuclear Cu(II) compound generating extremely small antiferromagnetism

The synthesis, optical and magnetic properties and X-ray crystal structure of [Cu(2-aminopyrimidine)2(OH)(CF3SO3)]2(2aminopyrimidine)2, a new dinuclear hydroxo-bridged copper(II) compound with a CuOCu angle of 97.96° and a very small antiferromagnetic interaction for which the singlet–triplet exchange parameter J, is described. The magnetic exchange coupling is almost negligible and, depending on the actual sample, varies from − 1.8 to − 7.2 cm − 1 .