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Two new polymeric compounds, [Mn(dca)2(4CN-py)2]n (1) and [Mn(dca)2(bpe)]n (2) where dca = dicyanamide anion, 4CN-py = 4-cyanopyridine and bpe = 1,2-bis(4-pyridyl)ethane, have been synthesised and characterised by X-ray crystallography and low temperature magnetic study. Compound 1 consists of a two-dimensional network of octahedrally coordinated Mn(II) cations bridged by dicyanamide anions. In this compound, the Mn(II) cation is linked by four dca bridging ligands and two monodentate 4CN-py ligands. Compound 2 is an one-dimensional chain of Mn(II) bridged by dca as well as bpe. Each Mn(II) in the chain is octahedrally coordinated by four dca and two bpe ligands. Variable temperature magnetic susceptibility measurements in the temperature range 300–2 K reveal the existence of weak antiferromagnetic interactions in both complexes (J = −0.154 cm−1, g = 2.01 for 1 and J = −1.25 cm−1, g = 2.00 for 2).

Three dinuclear copper(II) complexes [Cu 2 (pdc) 2 (dpyo)(H 2 O) 2 ] n ( 1 ), {[Cu 2 (pdc) 2 (dabco)(H 2 O) 2 ]·2H 2 O} n ( 2 ) and {[Cu 2 (pdc) 2 (bpp)(H 2 O) 2 ]·2H 2 O} n ( 3 ) [pdc, pyridine-2,6-dicarboxylate; dpyo, 4,4′-dipyridyl- N , N ′-dioxide; dabco, 1,4-diazabicyclo[2.2.2]octane and bpp, 1,3-bis(4-pyridyl)propane] have been synthesized and structurally characterized by single crystal X-ray diffraction analysis and thermal study. Hydrogen bonding interactions, formed by coordinated and lattice water molecules, lead to a supramolecular architecture in all of them. Thermogravimetric analyses reveal that the complexes undergo reversible deaquation–reaquation process.

A one-pot reaction of [Co(NO3)(2)center dot 6H(2)O and piperazine] with NH4SCN/NaSCN in water-methanol (1:1) solvent leads to two polymorphs of [Co(SCN)(4)(ppz-H)(2)] (ppz, piperazine) (I and II). X-ray crystal structure reveals both have same space group but the differences in the alignment of pendant SCN- leads to two polymorphs. In I, trifurcated N-H...S hydrogen bonding plays a prominent role in crystal packing leading to S...S interactions between SCN fragments but in II, no such trifurcation arises and thereby the crystal packing occurs through hydrogen bonding interactions only leading to a distinctly different network topology. TG/DSC and FT-IR study reveal they are enantiotropically related. (c) 2007 Elsevier Ltd. All rights reserved.

A one-pot reaction of three components [MnII, isophthalate dianion (isop) and 4,4′-dipyridyl N,N′-dioxide (dpyo)] in water/methanol (1:1) causes self-assembly resulting in two 3D supramolecular isomers of the same stoichiometry, {[Mn(isop)(H2O)2]·(dpyo)·(H2O)}n (colorless) (1) and {[Mn(isop)(H2O)(dpyo)0.5]·(dpyo)0.5·(H2O)2}n (pink) (2). Both isomers crystallize in the same crystal system (triclinic) and space group (P). The structural determination of 1 reveals an isophthalato-bridged 1D coordination polymer, {[Mn(isop)(H2O)2]n, having 16- and 8-membered rings where isophthalate acts simultaneously as chelating and bridging ligand connected to three metal centers. In isomer 2 the 1D chains transform to a 2D arrangement through bridging dpyo that replaces a water molecule at metal axial position. Both the crystal structures result in a 3D supramolecular network achieved through H-bonding among the 1D (in 1) or 2D (in 2) coordination polymers with lattice water and dpyo molecules and also by means of π-π interactions in 1. Low-temperature magnetic measurement indicates antiferromagnetic interaction in both the isomers and the best fits are given by the exchange parameters J = –0.56 ± 0.02 cm–1, g = 2.01 ± 0.01 and R = 3.1 × 10–5 for 1 and J = –1.06 ± 0.03 cm–1, g = 2.01 ± 0.01 and R = 2.8 × 10–5 for 2.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Three coordination complexes of Co(II)/Fe(II) with 4,4′-trimethylenedipyridine (bpp) and pseudohalides (SCN−, SeCN− and N3−) have been synthesized. The complexes have been characterized by X-ray single crystal structure determination. They are isomorphous having 2D layers in which two independent wavy nets display parallel interwoven structures. Pseudohalide binds metal centers through N terminal and occupies the trans axial positions of the octahedral metal coordination environment. Pseudohalide remains pendant on both sides of the polymeric layer and help the stacking through hydrogen bonding. The conformation of bpp in the interpenetrated nets is observed to be dependent on the choice of pseudohalide.

A three dimensional supramolecular network, {[Co(bpee)(H2O)4] · (tp) · 2(H2O)}n (1) [bpee = trans-1,2 bis(4-pyridyl)ethylene; tp = terephthalate dianion] has been synthesized and characterized by X-ray single crystal structure, magnetic measurement and thermal analysis. The structure determination reveals that the cobalt(II) ions, bridged by bpee and coordinated by four water molecules, give rise to covalently linked 1D polymeric chain. The parallel chains get involved in H-bonding with tp resulting in a 3D architecture. Upon heating 1, which is pink in color, transforms to [Co(bpee)(tp)] (1a, blue). The deaquated species (1a) reverts on keeping in humid atmosphere. Low temperature magnetic data indicate weak antiferromagnetic coupling.

Two coordination polymers, [Cu(bpp)(H 2 O) 2 (ClO 4 ) 2 ] n ( 1 ) and {[Cu(bpds) 2 (ClO 4 ) 2 ] · 1.5(H 2 O)} n ( 2 ) [bpp, 1,3-bis(4-pyridyl)propane and bpds, 4,4′-bipyridyl disulfide] have been synthesized and characterized by X-ray single crystal diffraction study and magnetic measurement. Both the coordination polymers display 1D chains with perchlorate anions acting as pendant ligands. In 1 undulated polymers are built by Cu(H 2 O) 2 (ClO 4 ) 2 units connected by single bpp and in complex 2 Cu(ClO 4 ) 2 fragments are linked by pairs of bpds ligands to form a double-stranded chain. The crystal packing evidences polymers of 1 involved in weak H-bonding interactions leading to a 3D supramolecular network. Magnetic study reveals weak antiferromagnetic interactions in both complexes.

The coordination polymer, {[Co(tart)(phen)]·6H2O}n (1) (tart, tartrate dianion; phen, 1,10-phenanthroline) has been synthesized and characterized by single-crystal X-ray structure determination, magnetic measurement and thermal analysis. The structural analyses reveal two adjacent parallel 1D–[Co(phen)-tart-Co(phen)]– coordination polymers zipped through π-π interactions. The lattice water molecules, forming a 1D water cluster, function as glue to form a 3D supramolecular network through an extended hydrogen bonding. A comparison highlighting the structural differences with the corresponding 2,2′-bipyridine (bpy) derivative, {[Co(tart)(bpy)]·5H2O}n (2) containing a less amount of lattice water molecules is discussed. The variable-temperature magnetic study of 1 has been carried out and interpretation of the already reported complex 2 has been re-visited: both polymers 1 and 2 show weak antiferromagnetic interaction. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Two new copper(II) complexes {[Cu(H 2 biim)(H 2 O)(suc)](H 2 O)} n ( 1 ) and {[Cu(H 2 biim) 2 (H 2 O)][Cu(H 2 biim) 2 (glut)](glutH)(NO 3 ) · 2.5H 2 O} n ( 2 ) (H 2 biim, 2,2′-biimidazole; suc, succinate dianion; glut, glutarate dianion) have been synthesized and characterized by single crystal X-ray diffraction study and thermal analysis. Complex 1 comprises of 1D zigzag coordination polymers, elongated along the crystallographic b -axis, connected through H-bonding and face-to-face π–π interactions to form a robust 3D network. Whereas complex 2 is built up of bischelated [Cu(II)(H 2 biim) 2 ] 2+ units, glutarate and nitrate anions and water molecules, held together through an extensive H-bonded system. The resulting 3D supramolecular architecture defines channels which are filled by lattice water molecules and disordered nitrate anions.

Four 3d–4f heterometallic coordination polymers, [Cu3(IDA)6Ln2] · n(H2O) [IDA = iminodiacetate dianion; Ln = Gd, n = 3 (1); Ln = Nd, n = 6 (2); Ln = Sm, n = 6 (3)] and [Cu(Cl)(NTA)Sm(H2O)6] · (ClO4) · (H2O) (4) [NTA = nitrilotriacetate trianion], have heen synthesized and characterized by single crystal X-ray diffraction analysis. Complexes 1–3 are isomorphous, showing a 3D coordination framework having tubular channels filled by lattice water molecules running parallel to the c axis. Whereas complex 4 is a 1D polymer of alternating copper and samarium ions connected by NTA, and the chains get involved in H-bonding interactions resulting in a 3D network. A low temperature magnetic study reveals ferromagnetic interactions for complex 1. Thermogravimetric and X-ray powder diffraction analyses of 1, 2 and 3 show that the covalently bonded 3D network remains almost unaffected after deaquation.

Three supramolecular complexes of Co(II) using SCN-/SeCN- in combination with 4,4‘-dipyridyl-N,N‘-dioxide (dpyo), i.e., {[Co(SCN)2(dpyo)2]·(dpyo)}n (1), {[Co(SCN)2(dpyo)(H2O)2]·(H2O)}n (2), {[Co(SeCN)2(dpyo)(H2O)2]·(H2O)}n (3), have been synthesized and characterized by single-crystal X-ray analysis. Complex 1 is a rare example of a dpyo bridged two-dimensional (2D) coordination polymer, and π-stacked dpyo supramolecular rods are generated by the lattice dpyo, passing through the rhombic grid of stacked layers, resulting in a three-dimensional (3D) superstructure. Complexes 2 and 3 are isomorphous one-dimensional (1D) coordination polymers [-Co-dpyo-Co-] that undergo self-assembly leading to a bilayer architecture derived through an (8) H-bonding synthon between coordinated water and dpyo oxygen. A reinvestigation of coordination polymers [Mn(SCN)2(dpyo)(H2O)(MeOH)]n (4) and {[Fe(SCN)2(dpyo)(H2O)2]·(H2O)}n (5) reported recently by our group [Manna et al. Indian J. Chem. 2006, 45A, 1813] reveals brick wall...

The complexes [Cu2(ox)(phen)2(H2O)2](NO3)2 (1), [Cu2(sq)(pmdien)2(H2O)2](ClO4)2 (2) and {[Cu3(pdc)3(4,4′-bipy)1.5(H2O)2.25] · 2.5(H2O)}n (3) [phen = 1,10-phenanthroline; pmdien = N,N,N′,N′,N″-pentamethyldiethylenetriamine; 4,4′-bipy = 4,4′-bipyridine; ox = oxalate dianion; sq = squarate dianion and pdc = pyridine 2,6-dicarboxylate] have been synthesized and characterized by X-ray single crystal structure determination, low temperature magnetic measurement and thermal study. Structure determination reveals that 1 and 2 are dinuclear copper(II) complexes bridged by oxalate and squarate dianions, respectively, while 3 is a hexanuclear species formed by three Cu(pdc)(H2O)-(4,4′-bipy)-Cu(pdc)(H2O) fragments, connected through long Cu–O(pdc) bonds in a centrosymmetric arrangement. In complex 1 H-bonds occurring between the coordinated water molecules and lattice nitrate anions result in eight-membered ring clusters with the concomitant formation of 1D supramolecular chain. The adjacent chains undergo π–π stacking forming a 2D architecture. In the crystal of 3 an extensive H-bonding scheme gives rise to a 3D supramolecular network. Low temperature magnetic study shows a strong antiferromagnetic coupling in 1 (J = −288 ± 2 cm−1, g = 2.21 ± 0.01, R = 1.2 × 10−6); and a very weak interaction in 2 and 3, the best-fit parameters being: J = −0.21 cm−1, g = 2.12 ± 0.01, R = 1.1 × 10−6 (2) and J = −1.34 cm−1 ± 0.1, g = 2.14 ± 0.01, R = 1.2 × 10−6 (3) (R defines as ∑ [ ( χ M ) obs - ( χ M ) calc ] 2 / ∑ ( χ M ) obs 2 ) .

Three new supramolecular networks of cobalt(II) and iron(II), {[Co(4,4′-bipy)(H2O)4] · (C5O5) · (H2O)2}n (1), {[Fe(4,4′-bipy)(H2O)4] · (C5O5) · (H2O)2}n (2) and {[Co2(bpds)2(C5O5)2(H2O)4] · (H2O)3}n (3) [4,4′-bipy = 4,4′-bipyridyl, bpds = 4,4′-bipyridyl disulfide, C 5 O 5 2 - = croconate dianion ] have been synthesized and characterized by X-ray single crystal structure determination and thermogravimetric analysis. All of these coordination networks feature 1D polymers. Complexes 1 and 2 have a comparable structure based on metal centers coordinated by four water molecules and bridged by 4,4′-bipy ligands to give rise to a linear chain. Crystal packing shows a 3D supramolecular architecture through H-bonding occurring between lattice croconate dianions and water molecules. Conversely complex 3 is formed by Co(C5O5)(H2O)2 units connected by bridging bpds resulting a polymer with a zig zag arrangement. The metal coordination sphere comprises of two chelating oxygens from the croconate dianion, two water molecules and two bpds nitrogens located in cis positions. The coordinated water and lattice water molecules undergo H-bonding to form a 3D supramolecular network.

Three cadmium complexes, [Cd(H2biim)2(SCN)2] (1), [Cd(H2biim)2(SeCN)2] (2) and [Cd(H2biim)2(dca)2] (3) [H2biim = 2,2′-biimidazole; dca = dicyanamide] have been synthesized and characterized by X-ray single crystal structure analysis. In complexes 1 and 2 monomeric units assemble into supramolecular helix whereas in 3 monomeric units assemble into supramolecular 2-D grid with (4,4) net topology. The appearance of helical topology in complexes 1 and 2 is due to the linear nature of SCN−/SeCN− whereas (4,4) net topology in complex 3 is due to the bent nature of dca−. In each case R12(7) hydrogen bonding synthon is attained facilitating the helical and (4,4) net topology.

Two novel polymeric carboxylato-bridged gadolinium(III) complexes of formulae, [Gd2(fum)3(H2O)4] · 2H2O (1) and [Gd2(tart)3(H2O)2] · 3H2O (2) (fum, fumarate dianion; tart, tartrate dianion) have been synthesized and characterized by single crystal X-ray diffraction studies, low-temperature magnetic measurements and thermal studies. The structure determination reveals a 3D network containing nine coordinated Gd(III) ions: for complex 1, the coordination sphere of gadolinium(III) comprises of two water molecules and seven oxygen atoms from fumarate dianions and for complex 2, a water molecule and eight oxygen donors from tartrate dianions. Variable-temperature magnetic susceptibility measurement reveals the existence of a weak antiferromagnetic coupling through the gadolinium ions. The best-fit parameters for complex 1, assuming a simplified structural model led to J = −0.0076 cm−1, g = 2.0, R = 2 × 10−5 whereas for complex 2 the double-layered structure inside the 3D network impedes the possibility to calculate the J value(s).

Three μ1,5-dicyanamide bridged Mn(II) and Co(II) complexes having molecular formula [Mn(dca)2(H2O)2]n · (hmt)n (1), [Co(dca)2(H2O)2]n · (hmt)n (2) and [Co(dca)2(bpds)]n (3) [dca = dicyanamide; hmt = hexamethylenetetramine; bpds = 4,4′-bipyridyl disulfide] have been synthesized and characterized by single crystal X-ray diffraction study, low temperature (300–2 K) magnetic measurement and thermal behavior. The X-ray diffraction analysis of 1 and 2 reveals that they are isostructural, comprising of 1D coordination polymers [M(dca)2(H2O)2]n [M = Mn(II), Co(II) for 1 and 2, respectively] with uncoordinated hmt molecules located among the chains. The [M(dca)2(H2O)2]n chains and the lattice hmt molecules are connected through H-bonds resulting in a 3D supramolecular architecture. The octahedral N4O2 chromophore surrounding the metal ion forms via two trans located water oxygens and four nitrogens from four nitrile dca. Complex 3 is a 1D chain formed by two μ1,5-dca and one bridging bpds. The octahedral N6 coordination sphere surrounding the cobalt ions comprises four nitrogens from dca and two from bpds. Low temperature magnetic study indicates small antiferromagnetic coupling for all the complexes. Best fit parameters for 1: J = −0.17 cm−1, g = 2.03 with R = 6.1 × 10−4; for 2, J = −0.50 cm−1, and for 3, J = −0.95 cm−1.

Two new cadmium (II) complexes [Cd(hmt)(dca)2] n (1) and [Cd3(hmt)2(SeCN)6(H2O)2] n (2) (hmt=hexamethylenetetramine, dca=dicyanamide) have been synthesized and characterized by X-ray single-crystal analysis. The complex 1 is a 2D rectangular grid of octahedral cadmium (II) with CdN6 chromophore where cadmium centers are doubly bridged by dicyanamide and hmt along a-axis, which are interlinked by dicyanamide running along c-axis. Whereas, complex 2 is a 1D chain of octahedral cadmium (II) with a three-leg ladder topology running along a-axis. The Cd(II) centers are doubly bridged through SeCN (infinite rail) along a-axis and singly bridged by hmt (two-step rung) along c-axis, having cadmium centers with CdSe2N3O and CdSe2N4 chromophores. The adjacent chains through H-bonding between coordinated water and hmt, and Se $$\cdots$$ Se interaction are extended to 2D supramolecular architecture.

Three new carboxylato-bridged polymeric networks of Mn-II having molecular formula [Mn(ox)(dpyo)](n) (1), {[Mn-2(mal)(2)(bpee)(H2O)(2)]center dot 0.5(bpee)center dot 0.5(CH3OH)}n, (2) and {[Mn-3(btc)(2)(2,2'-bipy)(2)(H2O)(6)]center dot 4H(2)O}(n) (3) [dpyo, 4,4'-bipyridine N,N'dioxide; bpee, trans-1,2 bis(4-pyridyl) ethylene; 2,2'-bipy, 2,2'-bipyridine; ox = oxalate dianion; mal = malonate dianion; btc = 1,3,5-benzenetricarboxylate trianion] have been synthesized and characterized by single-crystal X-ray diffraction studies and low temperature magnetic measurements. Structure determination of complex I reveals a covalent bonded 2D network containing bischelating oxalate and bridging dpyo; complex 2 is a covalent,bonded 3D polymeric architecture, formed by bridging malonate and bpee ligands, resulting in an open framework with channels filled by uncoordinated disordered bpee and methanol molecules. Whereas complex 3, comprising btc anions bound to three metal centers, is a 1D chain which further extends its dimensionality to 3D via pi-pi and H-bonding interactions. Low temperature magnetic measurements reveal the existence of weak antiferromagnetic interaction in all these complexes. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006).

Four cyano bridged Cu(II)–Ni(II) heterometallic complexes of general formula, [{Cu2(L)2Ni(CN)4}(ClO4)2 · xH2O]n (for 1, L = bis(3-aminopropyl) methylamine = medpt and x = 2.5; for 2, L = N-(2-aminoethyl)-1,3-propanediamine = aepn and x = 2; for 3, L = diethylenetriamine = dien and x = 1), [Cu(medien)Ni(CN)4]n (4) (medien = bis(2-aminoethyl)methylamine) have been synthesized and characterized by single-crystal X-ray diffraction analysis and low temperature magnetic study. In complexes 1–3, all the cyanide ligands of tetracyanonickelate(II) take part in bonding, connecting four adjacent copper(II) ions whereas in 4 trans-dicoordinated cyanide of Ni ( CN ) 4 2 - links two Cu(II) ions only. We have already reported, as communication, the structural features of complex 1 and of its dehydrated species 1a. A different chain stereochemistry is detected in the related polymeric frameworks 1–3, mainly dictated by the orientation assumed by the ancillary tridentate L ligand. Thermogravimetric analyses and X-ray powder diffraction of complexes 1–3 reveal that the complexes retain their crystallinity upon removal of lattice water molecules. The magnetic studies of complexes 1–4 were performed in the 2–300 K temperature range. For all the complexes, the χMT values from 300 to 60 K are very close and correspond to isolated Cu(II) ions with different average g values (>2.00). From 60 to 2 K, χMT values decrease indicating weak antiferromagnetic coupling.

Three new metal–organic hybrid polymeric networks of CoII and MnII with the molecular formulae [Co(bpp)(tp)(H2O)2] (1), [Mn(bpds)(tp)(H2O)2]·(bpds) (2), and [Mn(4,4′-bipy)(H2O)4]·(tp) (3) (bpp = 4,4′-trimethylenedipyridine; bpds = 4,4′-bipyridyl disulfide; 4,4′-bipy = 4,4′-dipyridyl; tp = terephthalate) have been synthesized and characterized by single-crystal X-ray diffraction studies, low temperature (300–2 K) magnetic measurements, and thermal behaviors. The structure determination of complexes 1 and 2 reveals a parallel interpenetrated structure of 2D layers with (4,4) topology, with metal ions at the nodes connected through tp and N,N-donor coligands. The octahedral N2O4 chromophore surrounding the metal ion results from trans located tp oxygens, two water molecules, and two nitrogen donors of the co-ligands in the cis position. The presence of uncoordinated bpds between the interpenetrated layers leads to the formation of a wafer-like structure for 2. In complex 3, however, manganese(II) ions bridged by 4,4′-bipy and coordinated by four water molecules give rise to a 1D polymeric chain. The adjoining chains encapsulate terephthalate anions (tp) to give a 3D structure through H-bonding. Low-temperature magnetic data indicate weak antiferromagnetic coupling in complexes 1 and 2. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

Two polymeric azido bridged complexes [Ni2L2(N-3)(3)](n)(ClO4). (1) and [Cu(bpdS)(2)(N-3)],(ClO4),(H2O)(2.5n) (2) [L = Schiff base, obtained from the condensation of pyridine-2-aldehyde with N,N,2,2-tetramethyl-1,3-propanediamine; bpds = 4,4'-bipyridyl disulfide] have been synthesized and their crystal structures have been determined. Complex 1, C26H42ClN15Ni2O4, crystallizes in a triclinic system, space group P1 with a 8.089(13), b = 9.392(14), c = 12.267(18) angstrom, a = 107.28(l), b 95.95(1), gamma = 96.92(1)degrees and Z = 2; complex 2, C20H21ClCuN7O6.5S4, crystallizes in an orthorhombic system, space group Pnna with a = 10.839(14), b = 13.208(17), c = 19.75(2) angstrom and Z = 4. The crystal structure of I consists of 1D polymers of nickel(L) units, alternatively connected by single and double bridging mu-(1,3-N-3) ligand with isolated perchlorate anions. Variable temperature magnetic susceptibility data of the complex have been measured and the fitting,of magnetic data was carried out applying the Borris-Almenar formula for such types of alternating one-dimensional S = 1 systems, based on the Hamiltonian H = -J Sigma(S2iS2i-1 + aS(2i)S(2i+1)). The best-fit parameters obtained are J = -106.7 +/- 2 cm(-1); a = 0.82 +/- 0.02; g = 2.21 +/- 0.02. Complex 2 is a 2D network of 4,4 topology with the nodes occupied by the Cu-II ions, and the edges formed by single azide and double bpds connectors. The perchlorate anions are located between pairs of bpds. The magnetic data have been fitted considering the complex as a pseudo-one-dimensional system, with all copper((II)) atoms linked by [mu(1,3-azido) bridging ligands at axial positions (long Cu...N-3 distances) since the coupling through long bpds is almost nil. The best-fit parameters obtained with this model are J = -1.21 +/- 0.2 cm(-1), g 2.14 +/- 0.02. (c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005).

One 3D and one 2D μ1,5-dicyanamide bridged NiII complexes having molecular formula [Ni(L1)(dca)2] (1) and [Ni2(L2)2(dca)4] · 0.5H2O (2) (L1 = 4-(2-aminoethyl)-morpholine, L2 = 1-(2-aminoethyl)-piperidine and dca = dicyanamide dianion) have been synthesized. X-ray single crystal analyses and low temperature magnetic measurements were used to characterize the complexes. Complex 1 represents a 3D structure where each metal ion is chelated by morpholine ligand (L1) and connected by four μ1,5-dca. Whereas complex 2 shows an undulated 2D structure with grid of (4,4) topology having two crystallographically independent NiII centers in similar octahedral environment where each metal center is chelated by one piperidine ligand (L2) and coordinated by four μ1,5-dca. Magnetic measurements of both the complexes indicate weak antiferromagnetic interactions through the μ-1,5-dca bridging ligands.

A one-pot reaction of CuCl2 · 2H2O and malonic acid leads to a novel three dimensional inorganic–organic hybrid framework, [Na2Cu(mal)2(H2O)2]n, (1) (mal = malonate dianion). Single crystal X-ray structure of 1 reveals that it is a novel heterometallic three dimensional coordination-polymeric network which consists of interlocked anionic Cu–malonate and cationic Na–water–malonate sheets, where malonate dianion functions as an unprecedented heptadentate ligand. Low temperature magnetic study reveals that the compound is weak ferromagnetically coupled and this is supported by magneto-structural correlation. Thermogravimetric analyses are performed and it is observed that complex 1 upon heating finally transforms to CuO, which is evident by X-ray powder diffraction technique. Controlled solid state thermolysis of complex 1 at ∼850 °C for 24 h leads to the formation of CuO nanorods, which is confirmed by scanning electron microscopy and X-ray powder diffraction technique. The nanorods formed here have average diameters of ca. 40–200 nm and lengths up to 13 μm.

Two new polymeric complexes of copper(II), [Cu(L1)(μ-fum)(μ-H2O)]n (1) (fum = fumarate dianion; L1 = N,N′-dimethylethane-1,2-diamine) and [Cu(L2)(μ-tp)]n (2) [tp = terephthalate dianion; L2 = N-(2-aminoethyl)-3-amino-1-propanol], have been synthesized. The molecular structures are determined by X-ray crystallography. Complex 1 is a fumarato-bridged zig-zag 1D chain of CuII−L1, which is extended to a 3D coordination polymer through bridging water molecules. Complex 2 is a chain of CuII in which the terephthalate anions bridge in alternate bis(bidentate) and bis(monodentate) fashions. The coexistence of such types of bridging modes of terephthalate ions in a single molecule is unprecedented. The chelating terephthalate ion is linked to an equatorial and an axial site of consecutive metal ions, while the other terephthalate ion is axially linked to CuII centers. Both the complexes are characterized by variable-temperature susceptibility measurements at room temperature down to 4 K. Fitting of the magnetic data reveals the existence of weak antiferromagnetic interactions through the bridging dicarboxylate pathways. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Two polymeric MnII complexes, [(m-phth)(Mn)(bpp)2]·0.5H2O (1) and [(mal)2(Mn)2(H2O)2(hmt)] (2) [mal = malonate; hmt = hexamethylenetetramine; bpp = 1,3-bis(4-pyridyl)propane; m-phth = 1,3-benzenedicarboxylate] have been synthesized. Complex 1 consists of 1D chains (with monocoordinated bpp) that are held together to form a 2D extended network of hydrogen bonding between lattice water molecules and uncoordinated bpp donors. Variable-temperature magnetic susceptibility data of the complex have been fitted applying the formula used for dinuclear complexes of MnII ions, considering interdimer interactions (J′). The following parameters were obtained from the best fit: J = −0.88 ± 0.02 cm−1, J′ = −0.1 cm−1 and g = 1.99 ± 0.01. The agreement factor R = Σ(χmTobsd. − χmTcalcd.)2/Σ(χmTcalcd.)2 is 1.110−5. Complex 2 is a 3D polymeric network where syn/anti-bridging malonate ligands and MnII centers are assembled in the form of [Mn(H2O)(mal)]n layers, which are further connected by hexamethylenetetramine. The magnetic data have been fitted considering the complex as a pseudo-two-dimensional sheet of MnII cations and malonate anions since the coupling through the hexamethylenetetramine ligand is almost zero. We have followed two approaches for fitting the data, (a) through the expansion series of Line’s equation for the S = 5/2 antiferromagnetic quadratic layer and (b) by using the equation based on an infinite 2D square lattice composed of isotropically coupled classical spin S = 5/2. Both approaches result in excellent theoretical fits and similar J values of −0.24 cm−1 and −0.21 cm−1 for the Line’s and Curely equations, respectively. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Reaction of Cu(ClO4)2 · 6H2O and pyrazine 2,3-dicarboxylate (pzdc) in aqueous ammonia medium results [Cu(pyrazine 2,3-dicarboxylate)(H2O)2] · H2O (1). The X-ray single crystal structure reveals that the compound is a 1D polymeric sinusoidal infinite chain which through intra- and inter-molecular hydrogen bonding interactions, involving lattice and coordinated water molecules with dicarboxylate oxygens and pyrazine nitrogens, gives rise to a 3D architecture. The variable temperature magnetic measurements show weak antiferromagnetic interactions between the Cu(II) centers. The best fit parameters through the typical equation for a uniform copper (II) chain are: J=−0.25 cm−1, g=2.17, R=1.3 × 10 −6 . The EPR spectrum does not alter with temperature (from r.t. to 4 K). The spectra are typical for square-pyramidal geometry of copper(II) ions, g∥=2.24 and g⊥=2.10 (average g=2.15, in good agreement to the value obtained by susceptibility fit).

Four succinato-bridged complexes of copper(II) have been synthesized. Complex 1, [Cu(2)(mu-OH(2))(2)L(bpy)(2)(NO(3))(2)](n) and 2, [Cu(2)(mu-OH(2))(2)L(phen)(2)(NO(3))(2)](n)(bpy = 2,2[prime or minute]-bipyridine; phen = 1,10-phenanthroline and LH(2)= succinic acid) exhibit 1D coordination polymer structures where both the nitrate ions are directly linked to the copper(ii) producing synthons in a 2D sheet. A novel 2D grid-like network, ([Cu(4)L(2)(bpy)(4)(H(2)O)(2)](ClO(4))(4)(H(2)O))n3, is obtained upon changing the nitrate by perchlorate anion in complex 1, where the channels are occupied by the anions. On changing the nitrate by tetrafluoroborate anion in complex 2, a novel octanuclear complex, [Cu(8)L(4)(phen)(12)](BF(4))(8).8H(2)O 4, is isolated. The coligand bpy and phen in these complexes show face-to-face (in 1,2,3,4) or edge-to-face (in 4 )pi-pi interactions forming the multidimensional supramolecular architectures. Interestingly, the appearance of edge-to-face pi-pi interactions in complex facilitates the formation of discrete octanuclear entities. Variable-temperature (300-2 K) magnetic measurements of complexes have been done. Complexes 1 and 2 show very weak antiferromagnetic (OOC-CH(2)-CH(2)-COO) and ferromagnetic coupling (mu-H(2)O). Complex 3 also shows antiferromagnetic (syn-syn mu-OCO), and ferromagnetic coupling (mu-O of the -COO group). Complex 4 with two types (syn-syn and syn-anti) of binding modes of the carboxylate group shows strong antiferromagnetic interaction.

Three new thiocyanato-bridged polymers of cadmium(II), [Cd(me4dpt)(SCN)2] n (1) [me4dpt = 3,3′-iminobis(N,N-dimethylpropylamine], [Cd(me2tn)(SCN)2] n (2) (me2tn = N,N′-dimethyl-1,3-propanediamine) and [{amphyH} {Cd(SCN)3}] n (3) (ampyH = 4-aminopyridinium cation), have been synthesized and their molecular structures determined through X-ray crystallography. In Complex 1 each square pyramidal mononuclear fragment is H-bonded (N − H…S) to form a 1D supramolecular chain. Complex 2 is a 1D coordination polymer in which each distorted octahedral cadmium(II) ion is linked with the four bridging thiocyanates and one diamine. The structure of 3 reveals anionic [Cd(SCN)3]− zigzag chains arranged in an approximately hexagonal array with the 4-aminopyridinum cations occupying triangular channels. Each chain is H-bonded (N−H…N) to form a 2D supramolecular network. Upon heating, 1 and 2 melt and transform to transparent solid masses at ambient temperature over a few days. On scratching, these turn to a fine powder. Th...

A mononuclear [Mn(mal)(bipy)(H2O)2] (1) and a dinuclear [Mn2(mal)(phen)3(H2O)2(Cl)]Cl (2) (mal=malonate dianion; bipy=2,2′-bipyridine and phen=1,10-phenanthroline) have been synthesised and structurally characterized by X-ray crystallography. The structure of complex 1 shows that each Mn(II) is linked with one bipy, two water molecules and a malonate ligand forming distorted octahedral environment and each mononuclear fragment through H-bonding interactions form 2D supramolecular network. The structure of complex 2 comprises to an asymmetric dinuclear cation which is bridged by a single anti–anti malonate ligand and chloride anions. The two distorted Mn(II) centres are separated by large distance 6.256(3) A due to the anti–anti bridging mode. The magnetic behavior of complex 2 studied in the temperature range 300–2 K corresponds to a weak antiferromagnetic coupling through the MnOCOMn anti–anti conformation. The magnetic data were fitted based on H=−2JS1·S2, yielding the intramolecular coupling constant J=−0.35 cm−1 with g=1.92 and R=1.255×10−4.

Two new metal-organic based polymeric complexes, [Cu(4)(O(2)CCH(2)CO(2))(4)(L)].7H(2)O (1) and [Co(2)(O(2)CCH(2)CO(2))(2)(L)].2H(2)O (2) [L = hexamethylenetetramine (urotropine)], have been synthesized and characterized by X-ray crystal structure determination and magnetic studies. Complex 1 is a 1D coordination polymer comprising a carboxylato bridged Cu(4) moiety linked by a tetradentate bridging urotropine. Complex 2 is a 3D coordination polymer made of pseudo-two-dimensional layers of Co(II) ions linked by malonate anions in syn-anti conformation which are bridged by bidentate urotropine in trans fashion. Complex 1 crystallizes in the orthorhombic system, space group Pmmn, with a = 14.80(2) A, b = 14.54(2) A, c = 7.325(10) A, beta = 90 degrees, and Z = 4. Complex 2 crystallizes in the orthorhombic system, space group Imm2, a = 7.584(11) A, b = 15.80(2) A, c = 6.939(13) A, beta = 90.10 degrees (1), and Z = 4. Variable temperature (300-2 K) magnetic behavior reveals the existence of ferro- and antiferromagnetic interactions in 1 and only antiferromagnetic interactions in 2. The best fitted parameters for complex 1 are J = 13.5 cm(-)(1), J' = -18.1 cm(-)(1), and g = 2.14 considering only intra-Cu(4) interactions through carboxylate and urotropine pathways. In case of complex 2, the fit of the magnetic data considering intralayer interaction through carboxylate pathway as well as interlayer interaction via urotropine pathway gave no satisfactory result at this moment using any model known due to considerable orbital contribution of Co(II) ions to the magnetic moment and its complicated structure. Assuming isolated Co(II) ions (without any coupling, J = 0) the shape of the chi(M)T curve fits well with experimental data except at very low temperatures.

Reaction of Ni(ClO4)2·6H2O with bis(3-aminopropyl)amine (dpt) and ammonium thiocyanate produces the novel thiocyanato-bridged nickel(II) compound [Ni(μ-NCS)(dpt)(NCS)]2[Ni(μ-NCS)(dpt)(NCS)]4, which has been structurally characterised. The structure determination reveals that there are two different molecules in the crystal lattice; one is dinuclear and other is tetranuclear. Low-temperature magnetic measurements show that there are ferro- as well as antiferromagnetic interactions. The ferromagnetic interaction arises from the dinuclear part and the doubly bridged part of the tetranuclear unit; the antiferromagnetic interaction occurs between singly bridged nickel centres in the tetranuclear unit. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

A tetranuclear ‘stepped wise’ copper(II) complex, [Cu4(μ2-OH)2(μ3-OH)2(2,2′-bipy)4Cl2]Cl2·6H2O has been synthesized and the crystal structure of the complex redetermined. The magnetic behavior has been investigated in the temperature range 300–4.2 K based on its novel binding modes of the OH−, i.e. OH− anions bridge the copper(II) centers in a bidentate (μ-2) as well as tridentate (μ-3) fashion and this shows ferromagnetic interactions. The fit of the experimental data was made by the irreducible tensor operator formalism (ITO) using the clumag program based on the Hamiltonian; H=−J1(S1S2+S3S4)−J2(S1S4)−J3(S1S3+S2S4) and the best fit parameters, assuming the g factors are identical and J2=J3, leads to J1=22.71 cm−1; J2=J3=0.34 cm−1 and g=2.10. The magnetic results are interpreted with structural parameters.

Two new polynuclear complexes of CuII, [Cu2(fum)(μ-OH)(bpy)2(H2O)](NO3)·2H2O (1) (fum = fumarate dianion, bpy = 2,2′-bipyridine) and [Cu(fum)(tmen)]·2H2O (2) (tmen = N,N,N′,N′-tetramethylethane-1,2-diamine), have been synthesized and structurally characterized by X-ray crystallography. Complex 1, C24H27Cu2N5O12, crystallizes in a triclinic system, space group P , with a = 10.168(14), b = 11.347(14), c = 14.74(2) A, and Z = 2; complex 2, C10H22CuN2O6, crystallizes in an orthorhombic system, space group Pbca, with a = 14.701(19), b = 14.899(19), c = 26.90(3) A, and Z = 16. Compound 1 is an alternating chain compound, with alternate repetition of bis(monodentate) (μ2) and bis(bidentate) (μ4) bridging modes of fumarate, showing ferromagnetic interaction between CuII ions through hydroxo bridges with a Cu−O−Cu angle of 108.5°. Compound 2 is a linear 1D zig-zag polymer. There are two copper(II) ions with equivalent coordination and geometry in the asymmetric unit, each of them bonded to a bidentate tmen ligand and to two different fumarate moieties. Magnetic susceptibility data were measured in the 300−2 K temperature range. The magnetic data for 1 were fitted by use of a ferromagnetic/antiferromagnetic alternating S = 1/2 chain system and show the following results: JF = +5.4 cm−1, JAF = −0.25 cm−1, g = 1.96. The susceptibility data of 2 were fitted by use of the Bonner−Fisher expression for antiferromagnetically coupled S = 1/2 local spins, giving the parameters J = −1.81 cm−1, g = 2.03.

Two novel polymeric networks of cadmium(II), [Cd2(ibn)(SeCN)4]n (1) (ibn=1,2-diamino-2-methylpropane) and [Cd(pyz)(SeCN)2]n (2) (pyz=pyrazine) have been synthesised and their molecular structures have been determined by X-ray crystallography. The polymer 1 consists of two 1D parallel chains of Cd(II), each having alternate tetrahedral (CdSe4) and octahedral (CdN6) Cd(II) centres bridged through selenocyanate, exhibiting symbiotic phenomena. The octahedral Cd(II) centre of one chain is linked with the tetrahedral Cd(II) centre of another chain through selenocyanate ligand resulting 1D ladder like structure. The complex 2 is a 2D network of octahedral Cd(II) (CdN4Se2) in which doubly selenocyanato bridged 1D coordination polymeric chains are linked through pyrazine ligand in a bc plane forming rectangular grid like structure.

Two 1D bi-bridging Cu(II) chains, catena-oxalate-bis[1-(2-aminoethyl)pyrrolidine-copper(II)]-0.5(squarate) perchlorate hydrate (1) and catena-pyrazine-oxalate-tetraaquo-dicopper(II) diperchlorate (2) have been synthesised and their molecular structures determined by X-ray crystallography. Compound 1 exhibits a polymeric arrangement with a ladder-like structure running parallel to crystallographic axis a, in which two [(Cu(ampy))2(ox)] chains (ampy = 1-(2-aminoethyl)pyrrolidine; ox = oxalate) are linked by squarate groups. The oxalate behaves simultaneously as bis-bridging and bis-monodentate towards four coplanar copper ions, a coordination mode which has never been reported for Cu(II). Compound 2 is characterized by a polymeric array with alternate repetition of bridging oxalate and ‘pyz’ (pyz = pyrazine). Low temperature magnetic behaviour reveals the existence of a dominant weak antiferromagnetic interaction within 1 whereas in 2 a strong antiferromagnetic interaction is observed. The results obtained experimentally corroborate the structural parameters in both 1 and 2.

A deep green complex, [Cu(L)(μ-Br)Br]2 (L = 1,4-diazacycloheptane) was synthesized and its crystal structure and magnetic properties have been studied. The structure determination reveals that in the binuclear unit each copper(II) occupies a distorted square pyramidal geometry in which each bridging bromine atom is simultaneously ligated in axial and equatorial positions between two adjacent copper(II) centres. The binuclear units are packed along the [101] direction. Each dimer is connected to its two nearest neighbours by two Cu–(μ-Br)⋯H–N–Cu hydrogen bonding interactions resulting in an infinite 1D ladder-like chain. The magnetic data were fitted considering the interdimer interactions using different models to obtain precise results and the susceptibility vs. temperature curve for the complex exhibits a maximum at 12 K indicating antiferromagnetic behaviour. Magneto-structural correlations have also been carried out.

One new two-dimensional and two one-dimensional organic/inorganic composite coordination polymers have been synthesised by the reaction of cadmium(II) halides with N-(3-hydroxypropyl)ethane-1,2-diamine (L) and structurally characterised. [Cd(L)Cl2]n (1) is a two-dimensional sheet which is built from intersecting zigzag chains and forms a honeycomb like (6,3) net where each octahedral cadmium is linked with two bridging chloride atoms, one pendant chloride atom, two chelated nitrogen atoms of L and an oxygen atom from a neighbouring ligand; each cadmium(II) acts as a branching centre. [Cd(L)Br2]n (2) is a bromo bridged one-dimensional chain in which the non-chelated part of ligand L binds a neighbouring cadmium(II) centre resulting in an alternating array of four- and twelve-membered rings. [Cd(L)I2]n (3) is an iodo bridged one-dimensional network of alternating octahedral (CdN4I2) and tetrahedral cadmium(II) (CdI4) centres. Upon heating the complexes exhibit an irreversible endothermic phase transition [95–133 °C, ΔH = 29.5 kJ mol−1 for (1); 83–128 °C, ΔH = 22.5 kJ mol−1 for (2) and 91–128 °C, ΔH = 15.5 kJ mol−1 for (3)] yielding transparent films of CdLCl2 (1a), CdLBr2 (1b) and CdLI2 (1c) respectively. The derived species (1a, 1b and 1c) do not revert on keeping them in a humid atmosphere (relative humidity ≈ 60%) for several days but exhibit a glass transition upon heating.

A three-dimensional supramolecular polymer of manganese(II), [{Mn(4,4′-bipy)(H2O)4}(C5O5)(H2O)2]n has been prepared and characterized by X-ray single crystal analysis. The polymer results from the mutual relationship of each coordination unit, [Mn(4,4′-bipy)(H2O)4]2+ through H-bonding between crystalline water and the encapsulated croconate dianion. Solid state thermal investigation shows stepwise elimination of water molecules and the 4,4′-bipyridine ligand.

Two novel 2D polymers of cadmium(II), [Cd(medien)(SeCN)2]n (1) (medien = N″-methyldiethylenetriamine) and [Cd2(iprdien)(SeCN)4]n (2) (iprdien = N′-isopropyldiethylenetriamine) have been synthesized and their molecular structure determined by X-ray crystallography. In complex 1 each octahedral cadmium(II) unit of a 1D coordination chain contains one pendant SeCN, binding through Se. These pendant SeCN form mutual relationships with other 1D chains through non-covalent interactions (H-bonding) giving rise to a 2D infinite sheet like structure. The molecular structure of 2 reveals a 2D infinite coordination polymer possessing alternating N-bonded octahedral and Se-bonded tetrahedral cadmium(II) centres exhibiting symbiotic phenomena. Both complexes undergo melting but complex 1 remains as a supercooled liquid in the temperature region 78–131 °C.

Reactions of nickel(II) salts with substituted ethane-1,2-diamine where one of the amine nitrogens is a part of a flexible cyclic ring, e.g. 1-(2-aminoethyl)piperidine (L), 1-(2-aminoethyl)pyrrolidine (L′) and 4-(2-aminoethyl)morpholine (L″) produce a number of complexes of the type: (i) Ni(AA)2X2 (where X=CF3CO2 −, SCN− and NO2 −; AA represents L/L′/L″); (ii) Ni(AA)2(CH3CN)2X2 (X=ClO4 − and NO3 −); (iii) Ni(AA)2(H2O)2X2 (X=CF3SO3 −, Cl−, Br− and I−); and (iv) Ni(AA)2(H2O)4X2 (X=0.5SO4 2−, 0.5SeO4 2− and CF3SO3 −). The complexes possess octahedral geometry. The major complexes upon desolvation retain trans-geometry, some of which are cis with respect to the counter-anion and a few of them are square planar. X-ray single crystal structure analyses of trans-[NiL2(CH3CN)2](ClO4)2, trans-[NiL2(NCS)2] (violet) and trans-[NiL″2(NCS)2] (sky-blue) have been done. The violet and sky-blue thiocyanato species have blue and green coloured isomers, respectively, and these pairs of isomers are proposed to be conformational isomers. Solid state thermal investigation of the complexes has been carried out. The complexes show thermochromism due to deaquation–anation/deaquation reaction/change of conformation. Only [NiL2](ClO4)2, [NiL′2(CF3CO2)2] and [NiL″2(NO2)2] undergo thermally induced phase transition. The effect of flexible ring size on diamine has been discussed.

A novel one dimensional (1D) bimetallic polymeric complex [catena-bis(μ-N-(aminoethyl)-3-aminopropanolato)-di-copper(II)-tetracyanonickelate(II)dihydrate] has been synthesized by the reaction of 1:1 mixture of CuCl2·2H2O and the hydoxyamine ligand, [N-(3-hydroxypropyl)ethane-1,2-diamine] with half equivalent of [Ni(CN)4]−2 in aqueous solution. X-ray quality single crystals were obtained by slow evaporation of the ammoniacal solution of the complex. The single crystal structure reveals that it is an alkoxo bridged Cu(II) dimer linked through [Ni(CN)4]2− in trans-fashion resulting in a 1D chain. The properties of the complex have been studied by variable temperature magnetic susceptibility measurements. The susceptibility data fit well with the Cu(lI) dimer equation to give 2J=−622 cm−1, g=2.05. The very high coupling parameter value clearly indicates the presence of very strong antiferromagnetic interaction between the Cu(II) ions.

A one-dimensional coordination polymer of nickel(II), [(μN,S-NCS)2{Ni(ampy)}]n (ampy=1-(2-aminoethyl)pyrrolidine) has been synthesized and characterized by X-ray single crystal analysis. Structure analysis reveals that each nickel(II) center is coordinated in a distorted octahedral fashion with four bridging thiocyanato ligands and one mesocyclic diamine ligand. The low temperature (300–18 K) magnetic measurement shows that the system is ferromagnetically coupled. The magnetic data are fitted to the de Neef equation, giving the parameters J=1.4 cm−1 and g=2.08.

The reaction of CuCl2·2H2O and Na2C4H2O4 (disodium fumarate) in dilute ammonia solution produces 1-D polymeric chain [Cu(μ-C4H2O4)(NH3)2]n(H2O)n. The crystal structure of the compound has been solved. The compound crystallizes in the monoclinic system, space group C2/m (No. 12), with chemical formula C4H10N2O5Cu, a = 13.955(5) A, b = 7.330(3) A, c = 8.927(2) A, β = 102.39(3)°, Z = 4. The interesting feature of the complex is that one of the carboxylic acid groups acts as a monodentate coordinating ligand whereas the remaining carboxylate moiety acts as a monoatomic bridging bidentate ligand. This unusual coordination behavior of fumarate anion produces a chain with alternate repetition of 4- and 14-member rings. The magnetic properties of the compound have been studied from room temperature to 4 K, which reveal the existence of a dominant ferromagnetic interaction with exchange coupling parameter values of JF = +12 cm-1 and JAF = −3.8 cm-1, using an alternating ferro- and antiferromagnetic chain model for...

Reaction of Cu(ClO4)2·6H2O with N,N′-dipropylethane-1,2-diamine (dpren, L), sodium oxalate and sodium azide in a 2:2:1:1 molar ratio results in a 1D coordination polymer of general formula [L(H2O)CuOxCu(H2O)L]2+, bridged through alternate azide and perchlorate anions, which, on mutual interaction with neighbouring 1D chains through H-bonding ia interchain free perchlorate anions, produces a sheet-like structure. A low temperature magnetic measurement of the complex shows the existence of strong antiferromagnetic interactions between the copper(II) ions. Least-squares fitting of the experimental magnetic susceptibility data using a modified Bleaney–Bowers equation for a dinuclear copper(II) system leads to the parameters J = −331.3 cm−1 and g = 2.05. The complex has also been characterised by X-ray single-crystal structure analysis and IR spectroscopy.

The brown nitro isomer, trans-[NiL2(NO2)2], 1 (L = N,N′-dipropyl-1,2-diaminoethane), was synthesized by adding L to a suspension of K4[Ni(NO2)6]·H2O in methanol. Complex 1 is metastable at ca. 298 K and transforms slowly to the greenish blue nitrito(O,O) isomer, cis-[NiL2(O2N)](NO2), 2. This transformation is accelerated with increasing temperature and slowed down on lowering the temperature (< 283 K). Complex 2 shows a reversible phase transition, 2↔3 (cooling: ΔH = 8.150 ± 0.004 kJ mol−1; 266–255 K; heating: ΔH = −7.960 ± 0.003 kJ mol−1; 257–268 K), whereas complex 1 does not exhibit any such transition. The structures of 1, 2 and 3 have been characterized by X-ray single crystal structure analyses, which reveal that 1 and 2/3 are nitro and nitrito(O,O) linkage isomers, respectively. Complexes 2 and 3 have essentially similar structures and their reversible transformation is supposed to be due to the change in thermal motion of the side chains on variation of temperature.

Two new copper(II) complexes, derived from an end-to-end azido linker and two different tridentate Schiff base ligands, have been synthesised and their crystal structures determined by X-ray diffraction methods. They are the single azido-bridged [Cu(L1 − H)(μ-1,3-N3)] n(H2O)2n (1) chain and the dinuclear [Cu2(L2)2(μ-1,3-N3)2(ClO4)2] (2) where L1 and L2 are two different tridentate Schiff bases obtained by condensation of salicylaldehyde with 4-(2-aminoethyl)morpholine and of pyridine-2-aldehyde with N,N-dimethylpropane-1,3-diamine, respectively. Structural results show that each copper(II) centre in 1 is in a square pyramidal geometry while in 2 the geometry of copper(II) is octahedral with one coordinated perchlorate in both copper(II) complexes. Variable temperature magnetic susceptibility data in the range of 300–2 K for 1 reveal the existence of intrachain weak antiferromagnetic interactions through the end-to-end azido coupler, while the data for 2 show the existence of unusual intradimer ferromagnetic interactions through the end-to-end azido pathway, which almost always leads to an anti-parallel spin orientation. Fitting of the data for 1 using the Bonner–Fisher model for an antiferromagnetically coupled chain of S = 1/2 local spins resulted in the parameters J = −4.3 cm−1, g = 2.1 and R = 4.0 × 10−4. Temperature dependent susceptibility data for 2 were fitted using the Bleaney–Bowers expression for a Cu(II) dimer, which led to the parameters J = +2.4 cm−1, g = 2.11 and ρ = 0.003.

A novel 1-D chain of Cu(II) with alternate single end-on and single end-to-end azido bridge having a very high Cu−N3(1,1)−Cu bond angle (129.98°) has been synthesized and characterized, which shows an intrachain antiferromagnetic interaction (J = −11.5 cm-1 for end-on bridge and −2.7 cm-1 for end-to-end bridge).

[NiL(SeCN) 2 (H 2 O)] [L=bis(3-aminopropyl)amine (dpt), ( 1 ), (2-aminoethyl)(3-aminopropyl)amine (aepn), ( 2 ) and bis(2-aminoethyl)methylamine) (medien), ( 3 )] have been synthesized and characterized in the solid state by X-ray single crystal analysis ( 1 and 2 ), IR, electronic spectra and magnetic measurement. Structure analyses of ( 1 ) and ( 2 ) reveal that the nickel(II) center is coordinated in a distorted octahedral fashion and the two SeCN groups are attached in trans position. Upon heating they undergo deaquation followed by color change, yielding dinuclear species bridging through selenocyanate. The deaquated dinuclear complexes have been characterized by IR, electronic spectra and magnetic susceptibility measurement.

The isomeric complexes trans-[NiL2(NCS)2] (violet) (1) and cis-[NiL2(NCS)2] (blue) (2) [L=1-(2-aminoethyl)pyrrolidine] have been synthesized, varying solvents and temperature, and their X-ray crystal structures have been determined. Both the isomers possess the same space group, P21/c, having distorted octahedral geometry.

The complexes [NiL3](NO2)2·2H2O (violet, 1) and cis-[NiL2(NO2)2]·0.5H2O (pink, 1b) (L=1,2-diamino-2-methylpropane) have been synthesized from solution. The X-ray single crystal structure analysis of compound 1b has been carried out, but the presence of a water molecule cannot be detected. Upon heating, complex 1b undergoes dehydration followed by an endothermic phase transition to produce trans-[NiL2(NO2)2] (1d). The violet species (1) also undergoes dehydration upon heating with deamination resulting (1d).