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Two novel dinuclear copper(II) complexes of formulae [Cu2(tren)2(bpda)](ClO4)4 (2) and [Cu2(tren)2(tpda)](ClO4)4 (3) containing the tripodal tris(2-aminoethyl)amine (tren) terminal ligand and the 4,4′-biphenylenediamine (bpda) and 4,4″-p-terphenylenediamine (tpda) bridging ligands have been synthesized and structurally, spectroscopically, and magnetically characterized. Their experimentally available electronic spectroscopic and magnetic properties have been reasonably reproduced by DFT and TDDFT calculations. Single crystal X-ray diffraction analysis of 2 shows the presence of dicopper(II) cations where the bpda bridging ligand adopts a bismonodentate coordination mode toward two [Cu(tren)]2+ units with an overall non-planar, orthogonal anti configuration of the N–Cu–N threefold axis of the trigonal bipyramidal CuII ions and the biphenylene group. The electronic absorption spectra of 2 and 3 in acetonitrile reveal the presence of four moderately weak d–d transitions characteristic of a slightly distorted trigonal bipyramid stereochemistry of the CuII ions. TDDFT calculations on 2 identify these transitions as those taking place between the four lower-lying, doubly occupied a2 (dyz)2, b2 (dxz)2, b1 (dxy)2, and a1 ( d x 2 - y 2 )2 orbitals and the upper, singly occupied a1 ( d z 2 )1 orbital of each trigonal bipyramidal CuII ion. Variable-temperature magnetic susceptibility measurements of 2 and 3 show the occurrence of moderate (J = −8.5 cm−1) to weak intramolecular antiferromagnetic couplings (J = −2.0 cm–1) [H = −JS1·S2 with S1 = S2 = SCu = ½] inspite of the relatively large copper–copper separation across the para-substituted biphenylene- (r = 12.3 A) and terphenylenediamine (r = 16.4 A) bridges, respectively. DFT calculations on 2 and 3 support the occurrence of a spin polarization mechanism for the propagation of the exchange interaction between the two unpaired electrons occupying the d z 2 orbital of each trigonal bipyramidal CuII ion through the predominantly π-type orbital pathway of the oligo-p-phenylenediamine bridges, as reported earlier for the parent compound [Cu2(tren)2(ppda)](ClO4)4·2H2O (1) with the 1,4-phenylenediamine (ppda) bridging ligand. Finally, a rather slow exponential decay of the antiferromagnetic coupling (–J) with the number of phenylene repeat units, –(C6H4)n– (n = 1–3), has been found both experimentally and theoretically along this series of oligo-p-phenylenediamine-bridged dicopper(II) complexes. These results further support the ability of linear π-conjugated oligo-p-phenylene spacers to transmit the exchange interaction between the unpaired electrons of the two CuII centers with intermetallic distances in the range of 7.5–16.4 A.

A new Co II /Co III hexanuclear complex, [Co 4 II Co 2 III (dea) 2 (Hdea) 4 )(piv) 4 ](ClO 4 ) 2 ·H 2 O 1 , has been obtained by reacting cobalt(II) perchlorate, diethanolamine, and pivalic acid (H 2 dea = diethanolamine and piv = pivalato anion). The cobalt ions are held together by four μ 3 and four μ 2 alkoxo bridges as well as by four syn – syn carboxylato groups. The hexanuclear motif contains four Co(II) and two Co(III) ions. The {Co II 4 Co III 2 (μ 2 -O) 4 (μ 3 -O) 4 } core can be described as a four face-sharing monovacant and bivacant distorted heterocubane units. The cobalt(III) ions are hexacoordinated. Two of the cobalt(II) are hexacoordinated, while the two others are pentacoordinated with a bipyramidal stereochemistry. The magnetic properties of 1 have been investigated in the temperature range 1.9–300 K. Compound 1 exhibits an overall antiferromagnetic behaviour with a ground singlet spin state.

A μ-alkoxo–μ-acetato trinuclear copper(II) complex, [Cu3(H2tea)(Htea)(CH3COO)2](ClO4) 1, has been synthesized by reacting copper(II) perchlorate, triethanolamine and sodium acetate. The unit cell contains two centrosymmetric, crystallographically independent trinuclear Cu(II) complexes and two ClO 4 - ions. The crystallographically independent trinuclear Cu(II) complexes differ mainly in some of their geometry parameters. The coordination environment of the central copper atom is square-planar, in one trinuclear entity, and elongated octahedral in the other one (in this last case, the coordination number of the central copper atom increases through the semicoordination of an oxygen atom arising from the aminoalcohol). The acetato groups exhibit the classical syn–syn bridging mode. The distances between the copper(II) ions in the two entities are, respectively: 3.043(3) and 3.034(4) A. The cryomagnetic investigation of 1 reveals a ferromagnetic interaction between the copper(II) ions (J = +84 cm−1), which is due to a countercomplementary effect of the acetato and alkoxo bridges.

The monouclear complex PPh4[Cr(bipy)(ox)2]·H2O (1) and the heterodinuclear compounds [Cu(bpca)(H2O)Cr(bipy)(ox)2]·2.5H2O (2) and [Cu(bpca)(H2O)Cr(phen)(ox)2]·2H2O (3) [PPh4+=tetraphenylphosphonium cation, bpca=bis(2-pyridylcarbonyl)amide anion, ox=oxalate dianion, bipy=2,2′-bipyridine and phen=1,10-phenanthroline] have been synthesized and characterized by single-crystal X-ray diffraction. Discrete [Cr(bipy)(ox)2]− mononuclear anions and tetraphenylphosphonium cations are present in 1 whereas the structures of 2 and 3 are made up neutral oxalato-bridged bimetallic CrIIICuII units. The chromium environment is distorted octahedral in the three complexes: two nitrogen atoms from a bidentate bipy (1 and 2) or phen (3) ligand and four oxygen atoms from two oxalate groups (1–3) build the coordination polyhedron around the chromium atom. The CrN(bipy) [2.055(3) and 2.078(3) A for 1 and and 2.060(3) and 2.066(3) A for 2] and CrN(phen) bond lengths [2.056(5) and 2.069(5) A (3)] are somewhat longer than the CrO(ox) ones [values in the ranges 1.944(2)–1.955(2) (1), 1.948(2)–1.960(2) (2) and 1.945(4)–1.953(4) A (3)]. The copper atom in 2 and 3 exhibits a distorted square-pyramidal surrounding: three bpca-nitrogen atoms [values of the CuN(bpca) bonds in the ranges 1.922(3)–2.017(3) (2) and 1.918(5)–2.004(6) A (3)] and a water molecule [CuOw=1.952(3) (2) and 1.952(5) A (3)] define the equatorial positions whereas an oxalate-oxygen atom occupies the axial site [CuOox=2.253(2) (2) and 2.325(4) A (3)]. The oxalate bridge in 2 and 3 exhibits a unusual bidentate/monodentate coordination mode, the metalmetal separation across this bridge being 5.283(1) (2) and 5.407(1) A (3). Magnetic susceptibility measurements of 1–3 in the temperature range 1.9–290 K reveal a Curie law behavior for the three complexes. The preparation of bimetallic systems by using [Cr(AA)(ox)2]− (AA=α-diimine type ligand) as a complex ligand towards coordinatively unsaturated metal complexes is analyzed and discussed.

Single crystals of the compound of formula [Ni(bipy)3]Cl2·5.5H2O (bipy=2,2′-bipyridine) have been prepared and structurally characterised by X-ray diffraction. The structure analysis reveals that the complex has an approximate D3 symmetry. The coordination sphere consists of six nitrogen atoms of the three-bipyridine ligands in an octahedral arrangement about the nickel. One of the chlorine ions is surrounded by twelve CH⋯Cl hydrogen bonds. Three kinds of layers are found in the crystal structure: (i) the Λ-[Ni(bipy)3]2+ cation; (ii) the water/chloride positions (O(1w)/Cl(21) to O(7w)/Cl(27)); (iii) the Δ-[Ni(bipy)3]2+ cation and a chloride ion (Cl(1)). The layers are stacked in the order (i), (ii), (iii) and (ii) almost parallel to the ab-plane. A thermogravimetric analysis shows that the water and chloride molecules were removed at 231 °C leading to the compound [Ni(C25H19N5)](s) according to elemental analysis and IR data. The plot of 1/χM versus T in the range 2.0–300 K obeys the Curie law.

The preparation, crystal structure and magnetic properties of PPh 4 [Cr(bpym)(C 2 O 4 ) 2 ]·H 2 O ( 1 ) and [Ag(bpym)][Cr(C 2 O 4 ) 2 (H 2 O) 2 ]·2H 2 O ( 2 ) (C 2 O 4 2− =oxalate dianion, bpym=2,2′-bipyrimidine and PPh 4 + =tetraphenylphosphonium cation) are described. The structure of 1 is made up of discrete (2,2′-bipyrimidine)bis(oxalato)chromate(III) anions, teraphenylphosphonium cations and uncoordinated water molecules. The structure of 2 consists chains of univalent silver cations bridged by bis-chelating 2,2′-bypyrimidine, cis -diaquabis(oxalato)chromate(III) anions and crystallisation water molecules. The chromium atom in 1 and 2 has a slightly distorted octahedral geometry with two bidentate oxalate groups ( 1 and 2 ), and one bidentate bpym ligand ( 1 ) or two cis -coordinated water molecules ( 2 ). The CrO(ox) bonds are in the ranges 1.951(3)–1.981(3) A ( 1 ) and 1.9575(12)–1.9585(14) A ( 2 ), values which are shorter than the CrO(w) bonds in 2 [1.9999(16) A]. The CrN(bpym) bond lengths are 2.064(4) and 2.090(4) A for 1 . The silver atom in 2 is disordered with two different four-coordinated environments from two bpym groups. One of these environments can be defined as a flattened tetrahedron with AgN(bpym) distances of 2.331(2) A (x2) and 2.360(2) A (x2) and the second one is distorted with values of the AgN(bpym) bonds in the range 2.132(18) and 2.59(2) A. The silver–silver separation across bridging bpym is 6.1854(8) A. Magnetic susceptibility measurements of 1 and 2 in the temperature range 1.9–290 K reveal the occurrence of weak antiferromagnetic interactions together with zero-field splitting effects. The use of the [Cr(bpym)(C 2 O 4 ) 2 ] − unit of 1 as a ligand towards different univalent and divalent metal ions is discussed in the light of the available structural information.

Two new mixed-ligand complexes of formula [Cu(bpym)(mal)(H2O)]·6H2O (1) and [Cu2(bpym)(mal)2(H2O)2]·4H2O (2) (bpym=2,2′-bipyrimidine and H2mal=malonic acid) have been synthesised and characterised by X-ray diffraction methods. The crystal structure of 1 consists of mononuclear [Cu(bpym)(mal)(H2O)] units in which the copper atom shows a slightly distorted square-pyramidal environment with two bpym-nitrogen and two malonate-oxygen atoms forming the equatorial plane and a water molecule in the axial position. The structure of 2 is built by centrosymmetric bpym-bridged dinuclear [Cu2(bpym)(mal)2(H2O)2] units, in which the geometry of each Cu(II) ion is similar to that found in 1. Malonate acts as a bidentate ligand in both compounds whereas bpym exhibits chelating and bis(chelating) coordination modes in 1 and 2, respectively. The intramolecular metal–metal separation in 2 is 5.445(1) A. The magnetic properties of 1 and 2 have been investigated in the temperature range 10–300 K. Complex 1 follows a Curie law for a magnetically isolated spin doublet, whereas 2 exhibits a relatively strong intramolecular antiferromagnetic coupling, J=−149 cm−1 (the spin Hamiltonian being defined as Ĥ=−JŜ1·Ŝ2).

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).

The reaction between copper(II) acetate with 2,2′-bipyridine and K3[Cr(C2O4)3] leads to the novel salt [Cu(bipy)2(CH3COO)][Cu(bipy)2(Cr(C2O4)3)]·∼10.5H2O, 1 (bipy=2,2′-bipyridine). The crystal structure of 1 consists of mononuclear cationic species [Cu(bipy)2(CH3COO)]+ and heterobinuclear anionic units, [Cu(bipy)2(Cr(C2O4)3)]−. The tris-oxalato-chromium entity behaves as a monodentate ligand toward the copper(II) ion within the complex anion. The distance between Cr(III) and Cu(II) across the bridging oxalato group is 5.056(2) A. The copper(II) ions exhibit a distorted trigonal bipyramidal surrounding in both cationic and anionic species. The π–π stacking interaction between bipy ligands of the neighboring [Cu(bipy)2(CH3COO)]+ mononuclear entities leads to chains of copper atoms running along the b axis. Magnetic susceptibility measurements of 1 in the temperature range of 1.9–290 K reveal a quasi-Curie law behavior, the magnetic coupling between Cr(III) and Cu(II) through the bridging oxalato group with the bidentate/monodentate coordination mode being negligible.

The copper(II) complex [Cu 2 (mal) 2 (H 2 O) 2 (4,4′-bpy)] ( 1 ) (H 2 mal=malonic acid and 4,4′-bpy=4,4′-bipyridine) has been prepared and its structure determined by single crystal X-diffraction methods. Compound 1 has a two-dimensional square grid network structure. The square grids are stacked parallel but in a staggered manner on each other along the c -axis, with an interlayer separation of 3.850(1) A. Each layer contains a large cavity of 15.784(1)×15.784(1) A with each edge shared by one malonate group and one 4,4′-bpy ligand and a small planar square of 4.644(1)×4.644(1) A with Cu(II) ions and malonate groups at each corner and side, respectively. Each copper atom is in a distorted square-pyramidal surrounding with three carboxylate-oxygen atoms from two malonate groups and one nitrogen atom from a 4,4′-bpy ligand building the equatorial plane and a water molecule in the axial position. Each 4,4′-bpy molecule exhibits the bis-monodentate bridging mode whereas the malonate simultaneously adopts the bidentate (at one copper atom) and monodentate (at the adjacent copper atom) coordination modes. The bridging carboxylato exhibits the anti – syn coordination mode. The magnetic properties of 1 have been investigated in the temperature range 1.9–300 K and they correspond to a dominant ferromagnetic coupling through bridging malonato within the small square defined by four copper(II) ions ( J =+12.4(1) cm −1 ) and much weaker intrasheet antiferromagnetic coupling between copper(II) ions through bridging 4,4′-bpy ( j eff =−0.052(1) cm −1 ).

Two new one-dimensional oxalato-bridged copper(II) compounds of formula [Cu(ox)L2]n (1) and {[Cu2(ox)2L%3]·L%}n (2) [ox oxalate dianion, L3-hydroxypyridine (pyOH) and L% 2-amino-4-methylpyridine (ampy)] have been synthesized and characterized by FT-IR spectroscopy, variable-temperature magnetic measurements and single-crystal X-ray diffraction. The crystal structure of 1 comprises chains of copper atoms in which cis-[Cu(pyOH)2] 2 units are sequentially bridged by asymmetric bis-bidentate oxalato ligands with an intrachain copper‐copper separation of 5.548(1) A, . Each copper atom is six-coordinated: four oxygen atoms belonging to two bridging oxalato ligands and two nitrogen atoms from two 3-hydroxypyridine ligands build a distorted octahedral environment around the metal atom. As in 1, the structure of compound 2 is made up of chains of copper atoms bridged sequentially by bis-bidentate oxalato ligands. Two types of copper(II) ion, one being six-coordinated (Cu(1)) and the other five-coordinated (Cu(2)), alternate regularly within the chain. The environment around Cu(1) is elongated octahedral with two cis-coordinated pyridine‐nitrogen and two oxygen atoms from two oxalate ligands building the equatorial plane, the apical positions being filled by two oxalate-oxygen atoms. The environment around Cu(2) is distorted square pyramidal with four oxalato-oxygen atoms in the basal plane, and the pyridine nitrogen atom from one aromatic base in the apical position. Magnetic susceptibility data in the temperature range 2.0‐300 K reveal regular ferromagnetic (J 1.3 cm 1 ) and alternating antiferromagnetic (J66.6 cm 1 , aJ58.6 cm 1 ) chain behaviours for 1 and 2. The nature and magnitude of the magnetic coupling through the oxalato bridge in 1 and 2 are analysed and discussed in the light of the available structural data. © 2001 Elsevier Science B.V. All rights reserved.