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Two copper(II) complexes, [Cu 2 L 2 (μ 1,1 -N 3 ) 2 ]·2CH 2 Cl 2 ( 1 ) and [CuL(μ 1,5 -dca)] n (dca = dicyanamide) ( 2 ) have been synthesized using a tridentate Schiff base ligand, 1-[(3-methylamino-propylimino)-methyl]-naphthalen-2-ol (HL) and azide or dicyanamide as co-ligand. Both complexes are characterized by elemental analysis, IR and UV–Vis spectroscopy and single crystal X-ray diffraction studies. The coordination geometry around the copper center in complex 1 is as an elongated (4 + 1) square pyramid and that in complex 2 is square planar with the tridentate Schiff base ligand in the basal plane. Complex 1 is a centrosymmetric dimer in which metal centers are connected by the double μ- 1,1 -azido bridges. On the other hand, complex 2 is a 1D zigzag chain in which metal centers are connected by μ 1,5 -N(CN) 2 ligands. The catecholase like activity for both complexes have been studied by using 3,5-di-tert-butylcatechol (3,5-DTBC) as the substrate. Complex 1 shows higher activity ( k cat = 40.8 h −1 ) than that of complex 2 (27.6 h −1 ) towards such oxidation reaction. [ABSTRACT FROM AUTHOR]

Five new hetero-metallic nickel(II)–mercury(II) complexes, [(NiL 1 )HgCl 2 ] ( 1 ), [(NiL 1 ) 2 HgCl 2 ] ( 3 ), [(NiL 1 ) 2 Hg(N 3 ) 2 ] ( 4 ), [{(NiL 2 ) 2 Hg(N 3 )(μ 1,1 -N 3 )} 2 ] ( 5 ) and [{(NiL 2 ) 2 Hg(N 3 )(μ 1,1 -N 3 )HgCl 2 } 2 {Hg(N 3 )(μ 1,1 -N 3 )}] ( 6 ) have been synthesized by reacting metalloligands [NiL 1 ] or [NiL 2 ] (where H 2 L 1 is N,N′-bis(salicylidene)-1,2-ethylenediamine and H 2 L 2 is N,N′-bis(salicylidene)-1,3-propanediamine) with HgX 2 (X − = Cl − or N 3 − ) at different molar ratios. All five complexes have been characterised by X-ray single-crystal structural, elemental and spectroscopic analyses. In complex 1 , the Hg(II) ion is coordinated to two phenoxido oxygen atoms of one [NiL 1 ] moiety and two terminal chloride ions to form a NiHg dinuclear complex. In the trinuclear complexes 3 and 4 , the central Hg(II) ion is coordinated by two terminal [NiL 1 ] units through two phenoxido oxygens from each and two terminal chloride (in 3 ) or azide (in 4 ) ions. The centrosymmetric hexanuclear complex 5 consists of two trinuclear [(NiL 2 ) 2 Hg(N 3 )(μ 1,1 -N 3 )] units, where the phenoxido bridges connect two terminal Ni(II) atoms of the trinuclear units. In these trinuclear units, one azido ligand adopts a μ l,1 -briding mode between Hg and Ni whereas the other one is terminal. In the nonanuclear complex 6 , two tetranuclear [{(NiL 2 ) 2 Hg(N 3 )(μ 1,1 -N 3 )}HgCl 2 ] units are linked to a central Hg(II) positioned on a two fold axis, via chlorido, azido, and phenoxido bridges. The tetranuclear unit is formed by the addition of a HgCl 2 molecule to a trinuclear [(NiL 2 ) 2 Hg(N 3 )(μ 1,1 -N 3 )] unit, similar to that present in 5 . Complex 5 shows weak ferromagnetic interactions ( J = +2.1 cm −1 ) between the two octahedral Ni(II) ions through double phenoxido bridges with a Ni–O–Ni bond angle of 95.87(11)°. [ABSTRACT FROM AUTHOR]

An oxime based tridentate Schiff base ligand 3-[3-(dimethylamino)propylimino]butan-2-one oxime (HL) produced two dinuclear compounds [Cu2L2(H2O)](ClO4)2 (1) and [Cu2L2(H2O)](BF4)2 (2), and a hexanuclear compound [{Cu3(HL)3(O3ClO)(μ3-O)}2(μ-H)](ClO4)7 (3) when it was reacted with Cu(ClO4)2·6H2O or Cu(BF4)2·6H2O at different pH values. All three compounds have been structurally and magnetically characterized. Compounds 1 and 2 are dinuclear species in which the two square planar copper(II) ions are joined solely by the double oximato bridges. On the other hand, the hexanuclear compound 3 consists of two triangular Cu3O cores held together by a proton separated by an O···O distance of 2.498(10) Å. The three square pyramidal copper(II) ions at the corners of an isosceles triangle form a triangular core through central oxido (μ3-O) and peripheral oximato bridges. Each triangular Cu3O core is capped by an unusual triply coordinated (μ3-perchlorato-O,O',O") perchlorate anion. Variable-temperature (2-300 K) magnetic susceptibility measurements show that compounds 1-3 exhibit a strong antiferromagnetic interaction with J values -562.6, -633.1 and -636.0 cm-1 respectively. The X-band EPR data at low temperature clearly indicate the presence of a spin frustration phenomenon in complex 3. [ABSTRACT FROM AUTHOR]

Oxime-based tridentate Schiff base ligands 3-[2-(diethylamino)ethylimino]butan-2-one oxime (HL¹) and 3-[3-(dimethylamino)propylimino]butan-2-one oxime (HL²) produced the dinuclear complex [Ni2L¹2](ClO4)2 (1) and trinuclear complex [Ni3(HL²)3(µ3-O)](ClO4)4·CH3CN (2), respectively, upon reaction with Ni(ClO4)2·6H2O. However, in a slightly alkaline medium, both of the ligands underwent hydrolysis and resulted in tetranuclear complexes [{Ni(deen)(H2O)}2(µ3-OH)2{Ni2(moda)4}](ClO4)2·2CH3CN (3) and [{Ni(dmpn)(CH3CN)2}2(µ3-OH)2{Ni2(moda)4}](ClO4)2·CH3CN (4), where deen = 2-(diethylamino)ethylamine, dmpn = 3-(dimethylamino)-1-propylamine, and modaH = diacetyl monoxime. All four complexes have been structurally characterized. Complex 1 is a centrosymmetric dimer where the square planar nickel(II) atoms are joined solely by the oximato bridges. In complex 2, three square planar nickel atoms form a triangular core through a central oxido (µ3-O) and peripheral oximato bridges. Tetranuclear complexes 3 and 4 consist of four distorted octahedral nickel(II) ions held together in a rhombic chair arrangement by two central µ3-OH and four peripheral oximato bridges. Magnetic susceptibility measurements indicated that dinuclear 1 and trinuclear 2 exhibited diamagnetic behavior, while tetranuclear complexes 3 and 4 were found to have dominant antiferromagnetic intramolecular coupling with concomitant ferromagnetic interactions. Despite its singlet ground state, both 3 and 4 serve as useful examples of Kahn's model for competing spin interactions. High-frequency EPR studies were also attempted, but no signal was detected, likely due to the large energy gap between the ground and first excited state. Complexes 3 and 4 exhibited excellent catecholase-like activity in the aerial oxidation of 3,5-di-tert-butylcatechol to the corresponding o-quinone, whereas 1 and 2 did not show such catalytic activity. Kinetic data analyses of this oxidation reaction in acetonitrile revealed that the catalytic activity of 3 (kcat = 278.4 h-1) was slightly lower than that of 4 (kcat = 300.0 h-1). X-band EPR spectroscopy indicated that the reaction proceeded through the formation of iminoxyl-type radicals. [ABSTRACT FROM AUTHOR]

Abstract: Two phenoxido bridged dinuclear Cu(II) complexes, [Cu2(L1)2(NCO)2] (1), and [Cu2(L2)2(NCO)2]·2CH3OH (2), have been synthesized using the tridentate reduced Schiff-base ligands 2-[(2-dimethylamino-ethylamino)-methyl]-phenol (HL1) and 2-[(2-diethylamino-ethylamino)-methyl]-phenol (HL2) respectively. Re-crystallization of compound 2 from dichloromethane produced desolvated complex [Cu2(L2)2(NCO)2] (3). The compounds 2 and 3 are pseudopolymorphs or solvomorphs which differ in the crystal system (orthorhombic, Pbca for 2 and monoclinic, P21/n for 3). The complexes have been characterized by X-ray structural analyses and spectroscopic methods. In all three complexes Cu(II) is penta-coordinated having the geometry intermediate between distorted square pyramid and trigonal bipyramid with Addison parameter (τ)=0.33, 0.48 and 0.53 for 1, 2 and 3 respectively. Using 3,5-di-tert-butylcatechol (3,5-DTBC) as the substrate, the catecholase activity of complexes 1 and 2 has been studied in methanol solution; compound 2 shows slightly higher catecholase activity (k cat =98.4h−1) than compound 1 (k cat =64.2h−1). [Copyright &y& Elsevier]

Abstract: Three new trinuclear hetero-metallic copper(II)–cadmium(II) complexes [(CuL)2Cd (NCS)2] (1A and 1B), [(CuL)2Cd(NCO)2] (2) have been synthesized using [CuL] as so-called “ligand complex” (where H2L= N,N′-bis(salicylidene)-1,3-propanediamine) and structurally characterized. Crystal structure analyses reveal that all three complexes have trinuclear entity in which two square planar [CuL] units are bonded to a cadmium ion through double phenoxido bridges. The Cd(II) is in a six-coordinate distorted octahedral environment being bonded additionally to two mutually cis nitrogen atoms of terminal thiocyanate (in 1A and 1B) and cyanate (in 2). Complexes 1A and 1B have the same molecular formula but crystallize in different monoclinic unit cells (P21/c for 1A and P21/n for 1B) and can be considered as polymorphs. On the other hand, complex 2 is crystallized only in one form and its conformation is similar to that observed in 1A. A theoretical investigation shows that 1A is slightly more (2.25kcal/mol) stable than 1B. However, in the crystal lattice, 1A establishes a C–H/π interaction while 1B interacts through a C–H···S hydrogen bond to form dimer and the more favorable dimerization energy in the later (ca. 3kcal/mol) compensates the difference in the relative energy of the polymorphs. Complex 2 crystallizes only in one form and conformation of the molecule is similar to 1A. Analyses of the noncovalent interactions of 2 show a weakening of the dimerization energy compared to 1A or 1B. Moreover, the H-bonding interaction that facilitates the formation of 1B is unlikely to be established in 2. Therefore this polymorph is not isolated. [Copyright &y& Elsevier]

Abstract: Four new trinuclear hetero-metallic nickel(II)–cadmium(II) complexes [(NiL)2Cd(NCS)2] (1A and 1B), [(NiL)2Cd(NCO)2] (2) and [(NiL)2Cd(N3)2] (3) have been synthesized using [NiL] as a so-called “ligand complex” (where H2L= N,N′-bis(salicylidene)-1,3-propanediamine) and structurally characterized. Crystal structure analyses reveal that all four complexes contain a trinuclear moiety in which two square planar [NiL] units are bonded to a central cadmium(II) ion through double phenoxido bridges. The Cd(II) is in a six-coordinate distorted octahedral environment being bonded additionally to two mutually cis nitrogen atoms of terminal thiocyanate (in 1A and 1B), cyanate (in 2) and azide (in 3). Complexes 1A and 1B have the same molecular formula but crystallize in very different monoclinic unit cells and can be considered as polymorphs. On the other hand, the two isoelectronic complexes 2 and 3 are indeed isomorphous and crystallize only in one form. Their conformation is similar to that observed in 1A. [Copyright &y& Elsevier]

Three double phenoxido-bridged dinuclear nickel(II) complexes, namely [Ni2(L1)2(NCS)2] (1), [Ni2(L2)2(NCS)2] (2), and [Ni2(L3)2(NCS)2] (3) have been synthesized using the reduced tridentate Schiff-base ligands 2-[1-(3-methylamino-propylamino)-ethyl]-phenol (HL1), 2-[1-(2-dimethylamino-ethylamino)-ethyl]-phenol (HL2), and 2-[1-(3-dimethylamino-propylamino)-ethyl]-phenol (HL3), respectively. The coordination compounds have been characterized by X-ray structural analyses, magnetic-susceptibility measurements, and various spectroscopic methods. In all complexes, the nickel(II) ions are penta-coordinated in a square-pyramidal environment, which is severely distorted in the case of 1 (Addison parameter τ = 0.47) and 3 (τ = 0.29), while it is almost perfect for 2 (τ = 0.03). This arrangement leads to relatively strong antiferromagnetic interactions between the Ni(II) (S = 1) metal centers as mediated by double phenoxido bridges (with J values of -23.32 (1), -35.45 (2), and -34.02 (3) cm3 K mol-1, in the convention H = -2JS1S2). The catalytic activity of these Ni compounds has been investigated for the aerial oxidation of 3,5-di-tert-butylcatechol. Kinetic data analysis following Michaelis-Menten treatment reveals that the catecholase activity of the complexes is influenced by the flexibility of the ligand and also by the geometry around the metal ion. Electrospray ionization mass spectroscopy (ESI-MS) studies (in the positive mode) have been performed for all the coordination compounds in the presence of 3,5-DTBC to characterize potential complex-substrate intermediates. The mass-spectrometry data, corroborated by electron paramagnetic resonance (EPR) measurements, suggest that the metal centers are involved in the catecholase activity exhibited by the complexes. [ABSTRACT FROM AUTHOR]