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[Cu(en)(phen)2]+ is crystallized along with two phenanthroline and eight lattice water molecules either as a chloride or a nitrate salt. The cation has almost identical structural and spectral properties which correspond to a tetragonally elongated octahedral geometry with the en ligand in the equatorial plane. EPR parameters reveal a slight rhombicity in the coordination polyhedron. Even though both compounds have the same composition (except for the anions), the hydrogen bond networks involving the lattice water molecules and anions are quite different in the two compounds. There are also extensive π-stacking interactions involving the phenanthroline molecules, both coordinated and non-coordinated. The non-bonding interactions have a major directing role in the crystallization of the tris-chelate cation. The analogous mixed ligand complex of 2,2-bipyridine could not be crystallized.

Three new phenoxo-bridged dimeric compounds of MnIII with tetradentate Schiff bases (salpnH2, salmenH2 and acphpnH2) and pseudohalide ligands have been synthesized and characterized by crystallography and dc and ac magnetic measurements. Mn(salpn)NCO (1) and Mn(salmen)N3 (2) exhibit intra-dimer ferromagnetic exchange (J = 0.42(2) cm−1 for 1, J = 0.58(1) cm−1 for 2, H ˆ = - 2 J S ˆ 1 S ˆ 2 ). The χmT product of 1 continuously increases upon lowering temperature, reaching a value of 10.01 cm3 mol−1 K at 1.98 K. In the case of 2, the χmT product reaches a maximum value of 7.85 cm3 mol−1 K at 5.82 K and decreases upon further cooling to a value of 6.34 cm3 mol–1 K at 2 K, indicating the operation of inter-dimer antiferromagnetic interactions. Frequency dependence of ac magnetic susceptibility shows single-molecule-magnetic (SMM) behavior in the temperature range 2–10 K for both compounds. In sharp contrast, Mn(acphpn)N3 (3) exhibits antiferromagnetic exchange interactions. salpnH2 = N,N′-bis(salicylidene)-1,3-diaminopropane, salmenH2 = N,N′-bis(salicylidene)-1,2-diaminopropane and acphpnH2 = N,N′-bis(2-hydroxyacetophenone)-1,3-diaminopropane.

Two complexes of silver(I) with 4,5-diazafluoren-9-one (dafone) which are the first examples of Ag-dafone complexes were synthesized and structurally characterized. Crystals of [Ag(dafone)2]NO3 · H2O (1) contain two strictly planar four-coordinate Ag(I) complexes. The silver coordination polyhedron in [Ag2(4,4′-bpy)(dafone)4]BF4 (2) is a highly distorted tetrahedron. Its crystal structure is built by a two-fold interpenetration of identical porous networks. The unusual coordination in the two compounds (planar four-coordinate d10 ion in 1, chelation with two long Ag–N bonds in 2 and low bond valence sums in both complexes) is in part due to the large chelate bite of dafone, and in part due to the stacking and other intermolecular interactions influencing the coordination geometry of Ag(I). This was further probed through molecular simulation of [Ag(N–N)2]+ complexes using DFT calculations.

Two new mixed ligand complexes of copper(II) with acetylacetonate (acac), 2,2′-bipyridine (bpy) and 1,10-phenanthroline (phen) belonging to the class of cytotoxic and antineoplastic compounds known as CASIOPEINAS® were synthesized and structurally characterized. Crystals of both complexes [Cu(acac)(bpy)(H2O)]NO3 · H2O (1), [Cu(acac)(phen)Br] (2) contain square pyramidal Cu(II) complex species. In frozen solution both compounds give well resolved EPR spectra with very similar parameters.

Cationic metal complexes of dipicolinic acid (dipicH2) are stabilized by [Ce(dipic)3]2− ions in the three isomorphous crystals [M(dipicH2)(OH2)3][Ce(dipic)3] · 3H2O (M = Ni, 1; Cu, 2; Zn, 3). Magnetic dilution provided by the bulky anions leads to well-resolved EPR spectra in polycrystalline samples of 2. The cations have 4+2 coordination, the carbonyl atom of the carboxylic acid groups coordinating weakly from trans positions. In the case of 2 this steric distortion is augmented by Jahn–Teller distortion. All the three structures are satisfactorily modelled by calculations based on density functional theory (DFT). The switch of the Jahn–Teller axis upon deprotonation of the complex, leading to the neutral species Cu(dipic)(H2O)3, is also reproduced by DFT. Electronic transition energies as well as the g-tensor component of the d9 complex obtained are in good agreement with experiment. However, the calculated hyperfine coupling constants are in error. DFT also fails to satisfactorily account for the electronic transition in the d8 ion in 1.

Reaction of dipicolinic acid with ammonium ceric nitrate and barium chloride produces, by self-assembly, three coordination polymers having similar stoichiometry but very different network structures. The structure of Ba(dipicH2)(OH2)4Ce(dipic)3 · 4.6H2O (1) is built up of 1-D alternating chains of nine-coordinate Ce and Ba polyhedra, each having tricapped trigonal prismatic geometry. The structure of Ba(OH2)6Ce(dipic)3 (2), wherein a chain of nine-coordinate aquo-Ba polyhedra is threaded through the channel formed by a trigonal arrangement of the Ce ( dipic ) 3 2 - anions, is analogous to that of SrCl2 · 6H2O · Ba(OH2)4Ce(dipic)3 · 2H2O (3), a polymorph of 2 (formally its hydrate isomer), exhibits a layered network in which Ce and Ba coordination polyhedra are linked by dipic ligands to form a corrugated sheet structure and may be considered as a metal–organic analog of the PbO lattice.

Three examples of Cu(II) complexes with dafone, Cu(dafone)2Br2 (1), [Cu(dafone)2(H2O)2](NO3)2 (2) and [Cu(dafone)2(H2O)2](ClO4)2 (3) have been synthesized and characterized structurally and spectroscopically. All complexes show unsymmetric chelation of dafone with one Cu—N bond being much longer than the other. Powder diffuse reflectance spectra have been recorded for 1, 2 and the known complex, Cu(dafone)2Cl2 (4) and correlated with the molecular g-values for this relatively new type of Cu(II) chromophore. Compounds 1 and 2 were found to be sensitive to grinding leading to additional EPR signals for 1 and changes in the X-ray powder diffraction patterns.

Reaction of AgNO3 with excess 2-(aminomethyl)pyridine (amp) in water led to the crystallization of Ag(amp)NO3 (1). Nearly linear coordination of silver (I) by pyyridine-N and amino-N from two different amp molecules results in a polymeric chain structure of 1. The packing is stabilized by ring-ring stacking interactions between two inversion-related polymer chains. Oxidation of 1 with (NH4)2S2O8 resulted in an orange solution from which a magnetically dilute AgII complex was crystallized by the addition of NH4PF6. It gave a well-resolved EPR spectrum and is formulated as silver(II) picolinate co-crystallized with NH4PF6.

Non-bonded interactions stabilise a normal Ag(dmp)NO3 molecule and a highly distorted [Ag2(dmp)2NO3]+ in the crystal of Ag(dmp)NO3 · 2H2O. The structure consists of two complex molecules, a mononuclear Ag(dmp)NO3 and NO3 bridged dinuclear cation [Ag2(dmp)2NO3]+ . The coordination around Ag in Ag(dmp)NO3 is of a regular 3+1 type while the dinuclear cation has a highly distorted geometry. The ring-ring stacking, CH3-CH3 interactions and C-H · O H-bonding stabilise the two complex molecules.