Jorunn Sletten

Syntheses, crystal structures and magnetic properties of copper(II) polynuclear and dinuclear compounds with 2,3-bis(2-pyridyl)pyrazine (dpp) and pseudohalide as ligands

Abstract The preparation, crystal structures and magnetic properties of four heteroleptic copper(II) complexes with 2,3-bis(2-pyridyl)pyrazine (dpp) and azide, cyanate or thiocyanate as ligands are reported, [Cu(dpp)(N3)2]n (1), [Cu(dpp)(NCO)2]n (2), [Cu(dpp)(NCS)2]2 (3) and [Cu(H2O)(dpp)(NCS)2]2·2H2O (4). Compounds 1 and 2 are isomorphous, triclinic, space group P1, and consist of mononuclear building blocks featuring copper atoms with close to square planar coordination geometries. The mononuclear units are, however, associated into chains through weak axial Cu–N bonds formed by end-on asymmetrically bridging azido/cyanato groups and by pyridyl nitrogen atoms. Taking these contacts into account, copper may be described as elongated octahedral. Compound 3 is monoclinic, space group P21/c. The mononuclear building blocks are similar to those in 1 and 2, but in this case the association between these units is such as to form dinuclear molecules through end-to-end bridging thiocyanate with weak axial CuS bonds, yielding a square pyramidal environment of copper. Compound 4 is triclinic, space group P1, and features a mononuclear unit which contains an apically coordinated water molecule. This leads to a significantly weaker intermolecular Cu⋯S contact as compared to that found in 3, but an association into dinuclear units is structurally and magnetically evident. The shortest Cu⋯Cu separations occur across the azido, cyanato or thiocyanato bridges, respectively, which are coordinated equatorially to one unit and axially to the neighbouring unit; 3.568(1) (1), 3.547(1) (2), 5.432(1) (3) and 5.371(1) A (4). Variable temperature magnetic susceptibility measurements on compounds 1, 2 and 4 reveal weak antiferromagnetic coupling across the azido, cyanato and thiocyanato bridges, respectively (J-values of −2.3(1) (1), −1.0(1) (2) and −1.0(1) (4) cm−1).

Syntheses, crystal structures and magnetic properties of chromato-, sulfato-, and oxalato-bridged dinuclear copper(II) complexes

Abstract Four dinuclear copper(II) complexes of formula [Cu2(bpca)2(H2O)3(CrO4)]·H2O (1), [Cu2(bpca)2(H2O)3(SO4)]·H2O (2), [Cu2(bpca)2(H2O)2(C2O4)]·2H2O (3), and [Cu2(bpca)2(C2O4)] (4) [bpca=bis(2-pyridylcarbonyl)amide anion] have been synthesized and their magnetic behavior has been investigated as a function of temperature. The structures of 1–3 have been determined by single-crystal X-ray diffraction, whereas the structure of 4 was already known. The structures of this family of complexes are made up of neutral chromateO1,O1′ (1), sulfateO1,O1′ (2) and oxalateO1,O2:O1′,O2′-bridged (3 and 4) dinuclear copper(II) units. The two copper atoms within the dinuclear unit of the isomorphous compounds 1 and 2 show different surroundings: they exhibit distorted square pyramidal (Cu(2)) and octahedral (Cu(1)) surroundings with the three bpca-nitrogen atoms and either a chromate (1)/sulfate (2)oxygen atom (Cu(2)) or a wateroxygen atom (Cu(1)) defining the equatorial positions, whereas the axial sites are occupied by a water molecule (Cu(2) and Cu(1)) and a chromate (1)/sulfate (2)oxygen atom (Cu(1)). Each copper atom of the centrosymmetric compound 3 is six-coordinated with the three bpca-nitrogen atoms and an oxalateoxygen forming the equatorial plane, whereas the axial positions are occupied by the other oxalateoxygen and a water molecule. Complex 4 is also centrosymmetric, each copper atom exhibiting a distorted square pyramidal surrounding. The equatorial plane is the same as in 3, and an oxalateoxygen occupies the axial position. The intramolecular coppercopper distances are 3.660(1) A (1), 3.747(1) A (2) and 5.631(1) A (3) (5.442(1) A in 4). The magnetic study of 1–4 reveals the occurrence of weak intramolecular antiferro- (1 and 2) and ferromagnetic (3 and 4) interactions. The magnitude and nature of the magnetic coupling through these extended bridges are analyzed and discussed in the light of the available structural data.

Crystal structures and magnetic properties of the squarate-O1,On-bridged dinuclear copper(II) complexes [Cu2(phen)4(C4O4)](CF3SO3)2 · 3H2O (n=2) and [Cu2(bipy)4(C4O4)](CF3SO3)2 · 6H2O (n=3)

Abstract Two dinuclear copper(II) complexes of the formula [Cu2(phen)4(C4O4)](CF3SO3)2 · 3H2O (1) and [Cu2(bipy)4(C4O4)](CF3SO3)2 · 6H2O (2) [phen=1,10-phenanthroline, bipy=2,2′-bipyridine and C4O4 2−=dianion of 3,4-dihydroxy-3-cyclobuten-1,2-dione (squaric acid)] have been synthesized and characterized by single-crystal X-ray diffraction. Their structures consist of [Cu2(phen)4(C4O4)]2+ (1) and [Cu2(bipy)4(C4O4)]2+ (2) dinuclear copper(II) cations, uncoordinated CF3SO3 − anions and crystallization water molecules. The copper is in a distorted square pyramidal environment: one squarate-oxygen atom and three phen- (1) or bipy- (2) nitrogen atoms of two phen (1) or bipy (2) terminal ligands form a distorted square plane around the copper whereas the axial position is occupied by the remaining phen- (1) or bipy- (2) nitrogen atom. The squarate adopts the μ-1,2- (1) and μ-1,3- (2) bis(monodentate) coordination modes, the intradimer copper–copper separation being 4.912(2) (1) and 7.310(1) (2) A, respectively. Variable temperature magnetic susceptibility measurements reveal the occurrence of significant intramolecular antiferromagnetic coupling, the relevant parameters being J=−26.4 cm−1 and g=2.14 for 1 and J=−8.6 cm−1 and g=2.07 for 2 (J being the exchange parameter in the isotropic spin Hamiltonian Ĥ=−JŜA · ŜB). The influence of both the symmetry of the copper(II) centered magnetic orbitals and the coordination modes of the bridging squarate on the magnitude of antiferromagnetic coupling in related squarate-bridged copper(II) complexes is analyzed and discussed.

Syntheses, crystal structures and magnetic properties of new oxalato-, croconato- and squarato-containing copper(II) complexes

The preparation and magnetic investigation of five mononuclear copper(II) complexes of formula [Cu(pyim)(C2O4)(H2O)]·2H2O (1), [Cu(pyim)(C4O4)(H2O)2]·2H2O (2), Cu(pyim)(C5O5)·2.5H2O (3), [Cu(H2bim)(C2O4)(H2O)]·H2O (4) and [Cu(bpz)(C5O5)(H2O)] (5) [pyim=2-(2-pyridyl)imidazole, H2bim=2,2′-biimidazole, bpz=2,2′-bipyrazine, C2O42−=dianion of oxalic acid, C4O42−=dianion of squaric acid and C5O52−=dianion of croconic acid] are reported. The crystal structures of 1, 2, 4 and 5 have been determined. The copper atom has a distorted square pyramidal geometry in this family of complexes: two nitrogen atoms from the bidentate nitrogen donor [pyim (1 and 2), H2bim (4) and bpz (5)] and two oxygen atoms either from a chelating oxalate (1 and 4)/croconate (5) or from a monodentate squarate and a water molecule (2) build the basal plane whereas a water molecule fills the apical position (1, 2, 4 and 5). A semi-coordinated oxalate (1 and 4)/croconate (5) oxygen atom of a neighbouring molecule occupies the sixth coordination position, leading to centrosymmetric dinuclear units. Magnetic susceptibility measurements for 1–5 in the temperature range 2–290 K reveal the occurrence of weak intermolecular ferro- (1) and antiferromagnetic (2–5) interactions. The different strategies to use these neutral complexes as ligands in order to design polynuclear species are analyzed and discussed.

Synthesis crystal structure and magnetic properties of [Fe2(bpym)(C5O5)2(H2O)4]·2H2O and two polymorphs of [Fe2(bpym)(C4O4)2(H2O)6]·2H2O (bpym = 2,2′-bipyrimidine)

Abstract Two dinuclear iron(II) complexes of formulae [Fe2(bpym)(C5O5)2(H2O)4]·2H2O (1) and [Fe2(bpym)(C4O4)2(H2O)6]·2H2O (2) (bpym = 2,2-bipyrimidine, C5O52 = dianion of croconic acid (4,5-dihydroxycylopent-4-ene-1,2,3-trione) and C4O42 = dianion of squaric acid (3,4-dihydroxycyclobut-3-ene-1,2-dione)) were prepared and their crystal structures (at 103 K) determined by X-ray diffraction methods. The structure of 1 consists of neutral centrosymmetric [Fe2(bpym)(C5O5)2(H2O)4] units and water molecules of crystallization which are linked by an extensive network of hydrogen bonds. The coordination geometry around each iron atom is that of a compressed octahedron with bpym nitrogen atoms and croconate oxygen atoms in the equatorial position and water molecules in the axial positions. The croconate and bpym ligands adopt bidentate and bisbidentate coordination modes respectively. Compound 2 exhibits two different polymorphic forms, denoted 2i and 2ii. The two molecular structures are made up of neutral centrosymmetric [Fe2(bpym)(C4O4)2(H2O)6] units and water of hydration, the main difference between the two forms being in the packing and hydrogen bond pattern. Each iron atom has a highly distorted octahedral geometry with bpym nitrogen atoms, one squarate oxygen and a water molecule in equatorial positions, and water molecules in axial positions. Squarate and bpym ligands adopt monodentate and bisbidentate coordination modes respectively. The intradimer metal-metal separations are 5.829(2) (1), 5.869(1) (2i) and 5.941(3) A (2ii). The magnetic behaviourof 1 and 2i in the temperature range 290-2 K is characteristic of an intradimer antiferromagnetic coupling, the susceptibility curves exhibiting maxima at 11.5 (1) and 18.5 K (2i). A magnetostructural comparison with other bpym-bridged iron(II) complexes is carried out.

Complex formation between squarate (C4O42–) and CuIIL [L = 2,2′-bipyridyl, 2,2′ :6′,2″-terpyridyl or bis(2-pyridylcarbonyl)amide anion (bpca)] in dimethyl sulphoxide solution. Crystal structure of [Cu2(bpca)2(H2O)2(C4O4)]

A new dinuclear copper(II) complex [Cu2(bpca)2(H2O)2(C4O4)]1[bpca = bis(2-pyridylcarbonyl)amide anion and C4O42)= dianion of squaric acid (3,4-dihydroxycyclobut-3-ene-1,2-dione)] has been synthesised and characterized by spectroscopy, magnetic and X-ray diffraction methods. It crystallizes in the triclinic space group P with a= 7.222(2), b= 10.272(1), c= 10.362(2)A, α= 82.85(1), β= 70.89(2), γ= 69.94(2)° and Z= 1. The structure consists of neutral centrosymmetrical squarate-O1,O3-bridged dinuclear copper(II) units. The configuration around each copper atom is distorted square pyramidal with the three nitrogen atoms of bpca and one squarato oxygen atom in the basal plane and a water oxygen atom at the apex. Variable-temperature magnetic susceptibility measurements (4.2–300 K) revealed an extremely weak exchange interaction through squarate. The protonation of squarate and its complex formation with CuIIL (L = 2,2′-bipyridyl, 2,2′ : 6′2″-terpyridyl or bpca) have been investigated in dimethyl sulphoxide solution at 25°C and 0.1 mol dm–3 tetrabutylammonium perchlorate as supporting electrolyte. Co-ordination modes of squarate for this system are discussed on the basis of the thermodynamic and structural parameters and compared to those of the related oxalato complexes.

Copper(II)-assisted hydrolysis of 2,4,6-tris(2-pyridyl)-1,3,5-triazine. Part 3. Crystal structures of diaqua[bis(2-pyridylcarbonyl)amido]copper(II) nitrate dihydrate and aquabis(pyridine-2-carboxamide)copper(II) nitrate monohydrate

Copper(II) has been found to promote the hydrolysis of 2,4,6-tris(2-pyridyl)-1,3,5-triazine (tptz) to yield [bis(2-pyridylcarbonyl)amido]copper(II) and free pyridine-2-carboxamide, NC5H4CONH2. The compounds [Cu{(NC5H4CO)2N}(H2O)2]NO3·2H2O (1) and [Cu(NC5H4CONH2)2(H2O)][NO3]2·H2O (2), where (NC5H4CO)2N– is the bis(2-pyridylcarbonyl)amide anion (L), were grown from aqueous solutions of tptz and copper(II) nitrate. Crystals of (1) and (2) are triclinic, space group P and Z= 2, with a= 6.811(1), b= 10.211(1), c= 12.039(1)A, α= 88.65(1), β= 82.32(1), and γ= 89.79(1)° for (1) and a= 11.622(3), b= 11.280(3), c= 8.007(3)A, α= 90.33(2), β= 101.85(4), and γ= 115.28(3)° for (2). The copper(II) ion is five-co-ordinate in both structures and its co-ordination geometry is near square pyramidal. The three nitrogen atoms of the (NC5H4CO)2N– ligand and the oxygen atom of a water molecule form a distorted square plane around the copper ion in complex (1), whereas such a basal plane is built by the pyridine nitrogen and oxygen atoms of two carboxamides in (2). The axial position is filled by a water molecule in both cases. The proton association and acid dissociation constants of the complex [CuL(H2O)]+[equations (i) and (ii)] have been determined by potentiometry in aqueous solution: log K1=[CuL(H2O)]++ H+ [graphic omitted] [Cu(HL)(H2O)]2+(i), [CuL(H2O)]+ [graphic omitted] [CuL(OH)]+ H+(ii) 1.83(1) and log K2=–8.80(1)(25 °C, 0.1 mol dm–3 NaNO3). The co-ordination of L to copper(II) decreases the basicity of the imide nitrogen atom as shown by the low value of log K1. The value of the hydroxo stability constant falls within the range established for hydroxocopper(II) complexes with N-donor tridentate ligands. A discussion of the factors which determine the nature of the isolated products of this copper(II)-promoted hydrolysis is made in the light of the available structures.

Chains and channels in polynuclear copper(II) complexes with 2,3-bis(2-pyridyl)pyrazine (dpp) as bridging ligand; syntheses, crystal structures and magnetic properties

Abstract The preparation and crystal structures for three Cu(II) polynuclear, chain complexes with 2,3-bis(2-pyridyl)pyrazine (dpp) as bridging ligand are reported, [Cu(dpp)(H 2 O) 2 ] n (NO 3 ) 2 n ·2 n /3H 2 O ( 1 ), [Cu(dpp)(H 2 O) 2 ] n (CF 3 SO 3 ) 2 n ( 2 ), and [Cu(dpp)(H 2 O) 2 ] n (BF 4 ) 2 n ·2 n H 2 O ( 3 ). For the latter compound the crystal structure at four different temperatures have been studied. Variable-temperature magnetic susceptibility data and ESR measurements of 1 – 3 and of the related copper(II) chain [Cu(dpp)(H 2 O) 2 ] n (ClO 4 ) 2 n ·2 n H 2 O ( 4 ) (whose structure was previously reported) have been performed. Compounds 1 and 2 crystallize in the same trigonal space group, R 3 c ; 3 is orthorhombic, space group Pbca . Complexes 1 and 2 are built of linear dpp-bridged chains which extend along threefold screw axes. The copper atom has in each case an elongated octahedral geometry with pyrazine nitrogen atoms in axial positions. The prominent feature of the crystal packing is the supramolecular arrangement of six chains around a threefold inversion axis, creating channels housing the counter ions, and in the case of 1 , also crystal water. In 3 the chain is zig–zag shaped and extends along a twofold screw axis. Counter ions and crystal water are situated in channels formed between four symmetry related chains. At room temperature (r.t.) the X-ray results show a copper ion with a compressed octahedral coordination geometry, pyrazine and pyridyl nitrogen atoms binding in equatorial and axial positions, respectively. The low temperature X-ray studies of 3 show significant changes in the copper coordination geometry, strongly suggesting that the apparent compressed geometry at r.t. is due to a dynamic Jahn–Teller distortion. The Cu⋯Cu separations across the bridging dpp at r.t. are, 7.133(1) ( 1 ), 7.228(1) ( 2 ), 7.005(1) ( 3 ) and 7.002(2) A ( 4 ). X-band ESR spectra of 1 and 2 exhibit the pattern of Cu(II) in elongated geometry ( g ∣∣ > g ⊥ >2.0), whereas those of 3 and 4 exhibit inverse ( g ⊥ > g ∣∣ >2.0) patterns with a shoulder in the perpendicular signal. Complexes 1 – 4 exhibit a Curie law behaviour with very weak intrachain antiferromagnetic coupling, the relevant magnetic parameters being J =−0.27 cm −1 , g =2.11 for 1 , J =−0.17 cm −1 , g =2.09 for 2 , J =−1.38 cm −1 , g =2.15 for 3 , and J =−1.36 cm −1 , g =2.14 for 4 (the Hamiltonian being H =− JS A S B ).

Interchain interactions and three-dimensional magnetic ordering in Mn(II)Cu(II) chain compounds; crystal structure and metamagnetic properties of MnCu(pbaOH)(H2O)3·2H2O, with pbaOH = 2-hydroxo-1,3-propylenebis (oxamato)

Abstract Single crystals of the novel phase MnCu(pbaOH)(H2O)3·2H2O (A) have been obtained; pbaOH stands for 2-hydroxy-1,3-propylenebis(oxamato). A crystallizes in the monoclinic system, space group P21/c,with a = 21.212(4) ,b = 5.033(1), c = 14.246(2) A , β = 100.72(2)° and Z = 4. The structure consits of oxamato-bridged Mn(II)Cu(II) bimetallic chains running along the a-axis direction. The shortest metal-metal separations between adjacent chains related by, respectively, the unit cell translation along the b-axis direction and the glide translation along the c-axis direction involve metal ions of the same type, in contrast with what was found in the previously described phase MnCu(pbaOH)(H2O)3 (B). According to our interpretation of the three-dimensional (3-D) magnetic effects in bimetallic chain compounds, the topology of the spin carriers in A should favor a 3-D antiferromagnetic ordering, while B exhibits a 3-D ferromagnetic ordering. The study of the temperature dependence of the magnetic susceptibility as well as the temperature and field dependences of the magnetization have confirmed this prediction. The antiferromagnetic ordering occurs at 2.4 K. A magnetic field of 0.9 kOe is sufficient to overcome the weak interchain interactions, so that the compound may be described as a metamagnet built from ferrimagnetic chains.

Preparation, structural characterization and physical properties of palladium(II) and platinum(II) complexes of the biheteroaromatic ligand 2-(2′-pyridyl)quinoxaline (L)

Abstract The 1:1 and 1:2 reactions of [MX4]2− (M=Pd, Pt; X=Cl, Br) with the biheteroaromatic ligand 2-(2′-pyridyl)quinoxaline (L) were studied. The new complexes [PdCl2L] (1), [PdL2]Cl2 (2), [PtCl2L] (3), [PdBr2L] (4) and [PtBr2L] (5) were isolated and studied by a combination of conductivity measurements, X-ray powder patterns, thermal techniques (TG/DTG, DTA) and spectroscopy (IR, far-IR, Raman). Compounds 1 and 2 have also been characterized by using 1H and 13C NMR spectroscopies. The complex [PdCl2L] crystallizes in space group P21/c with a=9.842(1), b=10.223(1), c=15.130(1) A, β=122.70(1)°, V=1281.0(6) A3 and Z=4. Refinement of the structure gave a final R factor of 0.017 (Rw=0.024) for 2050 unique reflections having I>2.0σ(I). The X-ray crystal structure of 1 shows a slightly distorted square planar geometry around the PdII atom. The ligand L behaves as a bidentate chelate with the ligated atoms being the pyridine nitrogen and the nearest quinoxaline nitrogen. Similar monomeric, square planar structures are also assigned for 3, 4 and 5. A trans square planar structure is proposed for the [PdL2]2+ cation in 2. All data are discussed in terms of the nature of bonding and known and assigned structures. Compounds with the empirical formulae PtCl2L0.5 (3a) and PtBr2L0.25 (5c) were isolated during the thermal decomposition of 3 and 5; the vibrational studies of these thermally stable intermediates show that L acts as a tridentate bridging ligand and support complicated polymeric structures. The 1H NMR study of the 1:1 [PdI(dien)]I/L (dien=diethylenetriamine) reaction solution in DMSO-d6/MeOD reveals a monodentate quinoxaline coordination of L.