Raikko Kivekäs

Structure and magnetic properties of a syn-anti carboxylate bridged linear trinuclear copper(II) complex with ferromagnetic exchange interaction

Abstract The synthesis, crystal structure and magnetic properties are reported for the trinuclear compound [Cu(H2O)4{Cu(HL)(H2O)(ClO4)}2][ClO4]2·2H2O, where HL is the monodeprotonated form of 6-methylamino-1,3-dimethyl-5-[(2′-carboxyphenyl)azo]uracil. The compound crystallizes in the triclinic system, space0 group P 1 , with cell constants a=7.824(3), b=12.278(3), c=13.705(9) A, α=104.34(3), β=91.80(3), γ=103.37(5)° and Z=1. The structure was solved and refined to R=0.071 (Rw=0.064). The structure consists of trinuclear [Cu(H2O)4{Cu(HL)(H2O)(ClO4)}2]2+ cations, non-coordinated perchlorate anions and crystal water molecules, held together by a network of hydrogen bonds. The central copper is in an elongated octahedral CuO6 chromophore and the terminal copper atoms in distorted square-pyramidal CuNO4 chromophores. Adjacent copper atoms are linked by carboxylate groups in a syn-anti conformation. From the magnetic susceptibility measurements, the complex is found to exhibit weak ferromagnetic interaction between nearest-neighbour copper(II) ions. The magnitude and nature of the exchange coupling are discussed on the basis of the structural data.

SINGLY ANTI-ANTI CARBOXYLATE-BRIDGED ZIG-ZAG CHAIN COMPLEXES FROM A CARBOXYLATE-CONTAINING TRIDENTATE SCHIFF BASE LIGAND AND M(HFAC)2 M = MNII, NIII, AND CUII : SYNTHESIS, CRYSTAL STRUCTURE, AND MAGNETIC PROPERTIES

The reaction of M(hfac)2 with the tridentate Schiff base H2L (where H2L stands for the 1:1 condensation product of 2-imidazolecarboxaldehyde with β-alanine) leads to the complexes [M(HL)(hfac)]n [M = MnII, NiII, and CuII; hfac = hexafluoroacetylacetonate anion] (1–3). The structures of the complexes 1 and 3 have been solved by X-ray crystallographic methods. The structures are very similar and consist of infinite zig-zag chains, running parallel to the b axis, in which the metal ions are bridged sequentially by anti-anti carboxylate groups with intrachain metal–metal distances of 6.134 A for 1 and 6.239 A for 3. Each monodeprotonated HL ligand acts as a tridentate one to a metal(II) ion and as a monodentate one to a neighbouring metal(II) centre. Metal atoms exhibit distorted octahedral coordination spheres comprised of two oxygen atoms from the hexafluoroacetylacetonate ligand, three donor atoms from the HL ligand and the oxygen atom belonging to the carboxylate group of an adjacent molecule. The complexes 1–3 have been confirmed to be isomorphous and isostructural on the basis of X-ray powder diffraction and IR spectra. The magnetic properties of the three compounds were studied by susceptibility measurements as a function of the temperature and successfully analyzed in terms of the isotropic spin Hamiltonian for one-dimensional infinite chain systems to give the coupling parameters J = –0.91 cm−1, g = 2.03 (1); J = –13.2 cm−1, g = 2.24 (2); and J = 0.40 cm−1, g = 2.11 (3). The magnetic behaviour for all three complexes can be satisfactorily explained in terms of the conformation of the bridge and the interaction between the d orbitals of the metal centre and the bridge.

Modulation of the CC distance in disubstituted l,2-R2-o-carboranes. Crystal structure of closo l,2-(SPh)2-l,2-C2B10H10

Abstract 1,2-Cc-substituted o-carboranes, where Cc represents the cluster carbon atoms, display a range of experimental/computed Cc⋯Cc distances from 1.629/1.624 A for the unsubstituted parent compound 1,2-C2B10H12 (1) to 1.798/1.818 A for l,2-(SPh)2-l,2-C2B10H10 (5) 1 or 1.858(5)/1.826(5) for l,2-μ-SCH2(CH2OCH2)2CH2S-1,2-C2B10H10 (7). Different Cc⋯Cc distances can be achieved by modifying the substituents on the carbon of the cluster compound. The crystal structure of a new disubstituted o-carborane 1,2-(SPh)2-l,2-C2B10H10 (5) was elucidated by single crystal X-ray diffraction. Purely alkyl substituents alter the Cc⋯Cc distance of the parent compound very little, which implies that steric effects, although relevant, are not the major cause of the lengthening. In contrast, substituents with lone pairs alter the Cc⋯Cc distance substantially. Our calculations suggest that the cause of the elongation is the transfer of electron density from the available lone pairs on the substituents to the Ψ* low-lying virtual orbitals mainly distributed around Cc, producing a decrease in the Cc⋯Cc bond order and, thereby, an increase in the Cc⋯Cc distance. A Bader analysis shows that the electron density at the bond-critical point, which is found at the mid-point of the Cc⋯Cc distance, decreases considerably with the presence of lone pairs of the sulfur atoms bound to the Cc atoms of the carborane cage.

The formation of nido [7,8-(PR2)2-7,8-C2B9H10]− from closo 1,2−(PR2)2−1,2−C2B10H10 (R = Ph, Et, iPr or OEt): a process enhanced by complexation

Abstract To gain insight into the mutual influence of an electron-rich element directly connected to the carborane cage, the coordination behavior of phosphorus atoms directly bonded to the cage has been studied. The reactivity of bisphosphines [7,8−(PR2)2−7,8−C2B9H10]− ( R = Ph, Et, i Pr or OEt ) has been investigated. These new chelating ligands exhibit some similarities to the much used 1,2-diphenylphosphinoethane (diphos), such as the spacing between the two phosphorus atoms, and their five-membered ring chelating ability, but there are notable differences, and dissimilar ligating properties are expected. The differences are mainly due to the incorporated carborane cluster and can be summarized as follows: (1) the ligand is anionic, (2) the phosphorus atoms lie in an eclipsed conformation and (3) B(3)−H coordination to the metal is possible. To study the partial degradation of the closo clusters to the nido clusters enhanced by complexation, several metal complexes were treated with the closo ligands in ethanol. The crystal structures of [AuCl2 {7,8−(P(iPr2)2−7,8−C2B9H10}] and [RuCl2{7,8−(P(iPr2)2−7,8−C2B9H10}2] have been determined.

Procedure for the degradation of 1,2-(PR2)2-1,2-dicarba-closo-dodecaborane(12) and 1-(PR2)-2-R′-1,2-dicarba-closo-dodecaborane(12)

Abstract Monophosphines and bisphosphines bearing anionic groups derived from the 7,8-dicarba- nido -undecaborate unit, such as [7-PR 2 -8-Me-7,8-C 2 B 9 H 10 ] − and [7,8-(PR 2 ) 2 -7,8-C 2 B 9 H 10 ] − (R = phenyl, ethyl, isopropyl or ethoxy), were synthesized from closo -carborane precursors 1-PR 2 -2-Me-1,2-C 2 B 10 H 10 and 1,2-(PR 2 ) 2 -1,2-C 2 B 10 H 10 , respectively. In general, the C c P bond in the closo species is very susceptible degradation reactions, producing C c P cleavage and yielding the [7,8-C 2 B 9 H 10 ] 2 − anion. Good degradation conditions which retain the C c P found are toluene with a carborane-to-pipeeridine ratio of 1:50 and ethanol with carborane-to-piperidine ratio of 1:10. The aryl phosphines keep the C c P bond best and produce the highest yields. Phosphites also retain the C c P bond, but the phosphorus becomes positive and produces a zwitterionic species. Alkylphosphines are intermediate, depending on the bulk and nature of the R group in the −PR 2 unit. The crystal structure of [NMe 4 ][7,8-(PPh 2 ) 2 -7,8-C 2 B 9 H 10 ]·CH 3 CH 2 OH is described.

Copper(II) salicylideneglycinate complexes as potential antimicrobial agents

Abstract The reaction of an ethanolic solutions of N-salicylideneglycinatoaquacopper(II) hemihydrate with urea, pyridine, 2,4-dimethylpyridine, 3,5-dimethylpyridine, quinoline, 4-methylquinoline, isoquinoline, or 3-methylisoquinoline in an equimolar ratio resulted in solid products containing complexes of the type Cu(salgly)L with distorted square pyramidal coordination polyhedra. The products were characterized by elemental analysis, electronic and EPR spectra, and magnetic susceptibility measurements. Moreover, the crystal and molecular structure of N-salicylideneglycinatoureacopper(II) dimer was determined by single crystal X-ray diffraction methods. The copper(II) atoms are bridged by two phenolic oxygen atoms with a CuCu distance of 3.1093(11) A and CuOCu angle of 94.47(12)°. The antimicrobial effects have been tested on various strains of bacteria, yeasts and filamentous fungi.

Revising the [PdCl2(1,2-(PPh2)2-1,2-C2B10H10)] synthesis and comparison of its behavior with [PdCl2(1,2-(PiPr2)2-1,2-C2B10H10)]. Crystal structure of [PdCl2(1,2-(PPh2)2-1,2-C2B10H10)]

Abstract Two methods for the revised synthesis of [PdCl2(1,2-(PPh2)2-1,2-C2B10H10)] are described. They differ on the reagent complex, to say 1,2-bis(diphenylphosphino)-1,2-dicarba-closo-dodecaborane was mixed with [PdCl2(cod)] or [PdCl2(PhCN)] in non-nucleophilic solvents. The structure of [PdCl2(1,2-(PPh2)2-1,2-C2B10H10)] was determined by single-crystal X-ray study. The carborane cage is coordinated bidentately through the P atoms to the Pd(II) ion, the remaining two positions are occupied by two chloride ions which are mutually cis. Overall, the coordination about the metal can be described as a slightly distorted square-planar. The reaction of 1,2-bis(diisopropylphosphino)-1,2-dicarba-closo-dodecaborane in dichloromethane produced mostly a compound with similar formula, however some deboronation took place and [Pd2(μ-Cl)2{7,8-(PiPr2)2-7,8-C2B9H10}2] was also produced. Larger amounts of this dinuclear complex were obtained when the closo species was refluxed for few minutes in a mild nucleophilic solvent.

1-Diphenylphosphino-2-methyl-1,2-dicarba-closo-dodecaborane(12)

Two C atoms from two phenyl groups and one C atom of the 2-methyl-1,2-dicarba-closo-dodecaborane cage in the title compound, C 15 H 23 B 10 P, are bonded to the P atom in a pyramidal arrangement. In the carbaborane moiety, the C-C bond length is 1.702 (6) A; lengthening of this bond is discussed

Designed Synthesis of New ortho-Carborane Derivatives: from Mono- to Polysubstituted Frameworks

The use of nucleophilic and electrophilic processes allow the designed synthesis of several B-iodinated derivatives of o-carborane. Because of the straightforward Pd-catalyzed conversion of B-I to B-C bond with Grignard reagents, such as methylMgBr and biPhenylMgBr, both, symmetrical 3,6-R 2-1,2- closo-C 2B 10H 10 and asymmetrical 3-I-6-Me-1,2- closo-C 2B 10H 10 could be obtained. Not only conventional reactions in solution have been studied but also a highly efficient, clean and fast solvent-free procedure has provided successful results to regioselectively produce B-iodinated o-carborane derivatives by a careful control of the reaction conditions. The high number of nonequivalent leaving groups in boron iodinated o-carborane derivatives opens the possibility through B-C coupling to materials with novel possibilities and to self-assembling due to the enhanced polarizability of the C-H bond.

From mono- to poly-substituted frameworks: a way of tuning the acidic character of C(c)-H in o-carborane derivatives.

The incorporation of iodine atoms onto the boron vertices of the o-carborane framework causes, according to spectroscopic data, a uniform increase in the acidic character of the C(c)-H (C(c)= cluster carbon) vertices, whereas the incorporation of methyl groups onto the boron vertices of the o-carborane framework reduces their acidity. Methyl groups when attached to boron are electron-withdrawing in boron clusters, whereas iodine atoms bonded to boron act as electron donors. This has been proven on B-methyl and B-iodinated o-carboranes with NMR spectroscopy measurements and DFT calculations of natural bond orbital (NBO) charges, which show a cumulative buildup of positive cluster-only total charge (CTC) on B-methyl o-carboranes and a cumulative buildup of negative cluster-only total charge for B-iodinated o-carboranes.