Hilde Grove

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).

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 ).

Copper(II) complexes of 1,4,5,8,9,12-hexaazatriphenylene with oxalate, squarate, perchlorate as auxiliary ligands or counter ion

Abstract The crystal structures of [Cu(hat)(H2O)(ox)]·H2O (I), [Cu(hat)(H2O)3(sq)]·3H2O (II) and [Cu(hat)(H2O)2](ClO4)2·4H2O (III) have been determined from X-ray single crystal diffraction data (hat=1,4,5,8,9,12-hexaazatriphenylene, ox=oxalate, sq=squarate=dianion of 3,4-dihydroxy-cyclobut-3-ene-1,2-dione). Compound I crystallises in the triclinic system, space group P 1 with a=6.6626(10), b=9.2001(14), c=12.9954(19) A , α=103.301(15), β=91.414(21), γ=105.523(13)°, Z=2; compound II in the orthorhombic system, space group P212121 with a=6.9274(2), b=8.4327(3), c=34.0577(14) A , Z=4; and compound III in the monoclinic system, space group C2/c with a=22.6652(10), b=9.2220(10), c=16.1400(10) A , β=106.783(10)°, Z=8. In I chelating hat and oxalate ligands and a coordinated water molecule make up a square pyramidal coordination sphere. The mono-nuclear units so described are, however, connected into dinuclear entities through a weak axial interaction between copper and an oxalate oxygen of a neighbouring molecule. In II copper has a distorted, elongated octahedral coordination geometry, being surrounded by a chelating hat, a mono-dentate squarate and three water molecules. The copper atom in III is bound to two mono-chelating hat units and two water molecules, it is situated on a two-fold axis and features an inverted Jahn–Teller geometry with two short and four intermediate distances at room temperature. X-band ESR spectra of I and II at room temperature exhibit the pattern g∥>g⊥>2.0 corresponding to the dx2−y2 orbital ground state of copper(II) ion in elongated octahedral geometry in these complexes. In the case of complex III the room temperature spectrum exhibits the reverse pattern (g⊥>g∥>2.0); variable temperature X- and Q-band measurements reveal that the inverted spectrum is gradually converted to a normal axial spectrum as the temperature is lowered, signalling that the apparent compressed geometry at room temperature is caused by a 2D dynamic Jahn–Teller effect. Variable-temperature magnetic susceptibility measurements of I reveal the occurrence of a weak antiferromagnetic coupling ( J=−1.0(1) cm −1 with the Hamiltonian defined as H =−J S A · S B ) between the copper ions.

Syntheses, crystal structures and magnetic properties of one- and two-dimensional pap-containing copper(II) complexes (pap = pyrazino[2,3- f ][4,7]phenanthroline)

Three polynuclear complexes containing copper(II) and pyrazino[2,3-f][4,7]phenanthroline (pap) as the basic building blocks have been prepared [Cu2(pap)(H2O)2(NO3)3]n[NO3]n1, [Cu4(pap)4Cl7]nCln·15nH2O 2, and [Cu4(pap)4(H2O)4(C4O4)2]n[C4O4]n[NO3]2n·12nH2O 3, and their crystal structures and variable-temperature magnetic susceptibilities determined. Compound 1 is a single stranded zigzag chain where pap and nitrate alternate as bridges between the copper atoms. The copper coordination geometry is to a first approximation distorted square pyramidal, but with an additional semi-coordinated oxygen from non-bridging nitrate groups. The bridging nitrate coordinates in the apical position to both copper atoms. In 2 the basic structural unit is a cyclic, tetranuclear entity where copper atoms are bridged by pap. Two different pap bridges are present, one through only equatorial positions, the other coordinating equatorially and axially. These tetranuclear units are linked, through diagonally opposite corners, into chains by single atom chloro-bridges. The copper coordination geometry is distorted elongated octahedral. In 3 a tetranuclear building block, with structural characteristics similar to those found in 2, is present, but in this case coordinated squarate (3,4-dihydroxycyclobut-3-en-1,2-dionate) links these units into sheets. Neighbouring sheets are firmly connected by hydrogen bonds through uncoordinated squarate and water into a three-dimensional supramolecular structure featuring channels running normal to the sheets. The Cu⋯Cu separations across bridging pap are 6.809 A in 1, 6.887 and 7.297 A in 2, and 6.936 and 7.250 A in 3. Variable-temperature susceptibility measurements on 1–3 reveal the occurrence of very weak intramolecular antiferromagnetic interactions between copper(II) ions through bridging pap (the largest value of J being −2.5 cm−1).

Syntheses, crystal structures and magnetic properties of polynuclear1,4,5,8,9,12-hexaazatriphenylene (hat)-bridged copper(II) complexes

Three polynuclear compounds containing copper(II) and 1,4,5,8,9,12-hexaazatriphenylene (hat) as the basic building blocks have been prepared, [Cu4(hat)2Cl8]n·6nH2O 1, [Cu(hat)(H2O)2]n[NO3]2n2, and [Cu2(hat)(H2O)6]n[SO4]2n·2nH2O 3, their crystal structures determined and variable-temperature magnetic susceptibility data measured. The basic building block in 1 is the dinuclear [Cu2(hat)Cl4] entity, two such units being connected to tetranuclear units through relatively strong axial Cu–Cl bonds (out-of-plane di-μ-chloro bridges). Weaker axial Cu⋯Cl interactions link the units into a sheet structure. In 2 and 3 hat-bridged copper(II) chains extending along glide planes are present. hat serves as a bis-bidentate ligand in 2 and as a ter-bidentate ligand in 3; in the latter compound one of the copper atoms coordinated to hat does not participate in chain formation. The copper coordination geometries observed in these compounds are square pyramidal and elongated octahedral. hat coordinates either in only equatorial positions to copper (1), or alternates with one chelate in two equatorial positions and another in one equatorial and one axial position (2 and 3). The copper⋯copper distance across the hat bridge in 1 is 6.857(1) A and 3.517(1), 3.600(1) and 3.651(1) A across the three different di-μ-chloro bridges. In 2 the intrachain Cu⋯Cu distance is 6.797(1) A. Three different Cu⋯Cu distances across the hat bridge are found in 3, one of 6.789(1) A involving two equatorial Cu–N bonds across a pyrazine ring, and two of 7.117(1) and 7.186(1) A involving one equatorial and one axial Cu–N bond to a pyrazine. Variable-temperature susceptibility measurements on 1–3 reveal the occurrence of weak intramolecular antiferromagnetic interactions between copper(II) ions through bridging hat, the J values being −2.5 (1), −2.1 (2) and −2.4 cm−1 (3). In 1 the interaction across the di-μ-chloro bridge within the tetranuclear entity (J′) is found to be weak and ferromagnetic in character (ca. +0.7 cm−1).