Tris(pyrazoly1)methane ligands in which two or three of the pyrazole carbon atoms bear organic substituents (L1-L7) were synthesized from chloroform and the corresponding pyrazole under phase transfer conditions. Their behavior towards zinc salts was found to span the range from no reaction at all to hydrolytic destruction. One hydrolysis product isolated and structurally characterized was the perchlorate complex [ ( H P z~)~Z~-O C~O~] C~O~ ( l ) , other ones were the 2 : l complexes (HPz3),ZnBrz (2) and (HPz6),Zn(N03), (3, HPz" = substituted pyrazole). Zinc perchlorate and tris(trimethy1py-razoly1)methane (Lz) formed the octahedral binary complex [L~Zn](ClO,), (4) as evidenced by a structure determination.Zinc halides produced the 1 : 1 complexes L' . ZnBr, (5), L4 . ~~ ZnC1, (6), and L4 . ZnBr, ( 7 ) , which according to the structure determinations of 6 and 7 contain tetrahedral ZnNzHalz units with only bidentate tris(pyrazoly1)methane ligands. In contrast, the zinc nitrate complex L4 . Zn(N03), ( 8 ) was found to have an octahedral structure with monoand bidentate nitrate and tridentate L4. The bromide complex 7 was converted by silver perchlorate hydrate into the labile compound [L4.ZnBr]C104 (9) and then into the unstable product [L4.Zn-OHZ](C1O4), (lo), both presumed to contain zinc in a tetrahedral ZnN3Br or ZnN30 environment, respectively. The ease of hydrolytic self-destruction prevented the exploitation of the reactivity of 9 and 10 in analogy to that of the corresponding tris(pyrazoly1)borate zinc complexes.The coordination chemistry of zinc suffers from lability and low thermodynamic stabilities. As a result it is difficult to gain a reliable control over the access to or reactivity at specific coordination sites. One approach to reduce these problems consists of the use of encapsulating ligands. These types of ligands, typically tripodal chelators, have the property of occupying all but one or two of the coordination sites around the metal. Thus, the thermodynamic stability of the complexes is enhanced due to the chelate effect, and their reactivity is reduced to the functionality of the remaining coordination sites.Only a limited number of tripodal ligands has been used so far with the purpose of studying zinc complex reactivities, mostly with a view to modelling zinc-containing en- zymes. Among them are tris(imidazolyl)phosphanes['l, tris-(imidazolyl)methanols[21, tris(pyridylmethyl)amines[31, bis-(amin~ethyl)glycine[~], and bis(nier~aptoethyl)pyridines[~]. We contributed studies with tris(aminomethyl)ethane[6], cyclohe~anetriamines[~], tris(pyridyl)phosphane[8], and tris-(imida~olylmethyl)amines[~]. The most productive tripod ligands for zinc enzyme modelling, in our[lo~lll as well as in other hands [12], have been the tris(pyrazoly1)borates. The reason for their superior usability is the fact that their encapsulating properties can be enhanced by voluminous substituents in the 3-and 5-positions of the pyrazole rings.In order to exploit these favorable properties with uncharged ligands we set out...

A remarkable pattern of structural diversity has been observed for the conformation of octachloro-1,10phenanthroline (ocp) in its free form and in its d 10 metal complexes [M(ocp) 2 ] + , M ) Cu, Ag, and Cl 2 Hg(ocp). Ocp: C 12 Cl 8 N 2 , monoclinic, space group P2 1 /c, a ) 5.6390(10) Å, b ) 24.970(3) Å, c ) 10.4660(10) Å, β ) 101.33°, Z ) 4; [Ag(ocp) 2 ](PF 6 )‚CH 2 Cl 2 , C 25 H 2 AgCl 18 F 6 N 4 P, monoclinic, space group P2/n, a ) 13.185(2) Å, b ) 9.4740(10) Å, c ) 16.106(2) Å, β ) 92.05°, Z ) 2; Cl 2 Hg(ocp)‚2.5C 6 H 6 : C 27 H 15 Cl 10 HgN 2 , triclinic, space group P1 h, a ) 10.391While ocp is virtually planar in the previously characterized ion [Cu(ocp) 2 ] + , the analogous silver(I) complex contains slightly twisted ocp ligands. In contrast, both the free, noncoordinated ligand and its dichloromercury(II) complex exhibit distincly saddle-shaped ocp. Cl 2 Hg(ocp) in particular contains a rather distorted chelate ligand. Ab initio calculations at the 6-31G** level show a flat energy hypersurface for ocp with an absolute minimum at a saddle-shaped conformation and a second energy minimum, 2.7 kcal/mol higher, for the coplanar arrangement. Nonbonded interactions between the chlorine atoms are responsible for the structural flexibility and limited coordination ability of ocp; electronically, ocp is a good acceptor ligand with two stabilized and close-lying unoccupied π* orbitals but much reduced σ donor capacity.

C hlorinated A rom atics, C opper C om pounds, C rystal Structure, Electrochem istry, H eterocycles Perchlorinated derivatives o f the com m on a -d iim in e chelate ligands 2,2'-bipyridine and 1,10-phenanthroline w ere synthesized and tested fo r their coordination behavior tow ards metal ions. O ctachloro-l.lO -ph en an th ro lin e (ocp) was o b tained via chlorination with P C I5 under pressure (300°C, 18 h). It fails to form stable com plexes w ith e.g. Fe2+, M n2+, Ru2+, N i2+, Z n 2+ or Cd~+, but yields com plex cations [M (ocp)2]+ w ith M = Cu, Ag. The crystal structure an aly sis o f the red tetrafluoroborate o f the copper(I) com plex cation reveals a distorted tetrahedral coordination at the metal w ith a slight tendency tow ards the trigonal-pyram idal arrangem ent; two essentially planar ligands w ith sm all bite angles intersect at alm ost right angle. Relative to conventional bis( 1,10-phenanthroline)copper(I) com plexes with sim ilar structures, [C u(ocp)2]+ has oxidation and reduction potentials shifted positively by about 1 V which leaves the energy o f the m ain M LC T absorption features little changed. A ttem pts to synthesize R u C h (o c p )2 in D M F produced as substituted product a sym m etrical b is(dim ethylam ino)-hexachloro-l,10-phenanthroline w hich can be oxidized electrochem ically in tw o steps. In contrast to ocp, octachloro-2,2'-bipyridine (ocb) show ed no detectable com plexation with C u+ and a very neg ative reduction potential, most probably due to its inability to exhibit a low -energy coplanar conform ation.Transition metal complexes with perhalogenated ligands have been investigated as potential oxida tion catalysts [1], The reason is the lower activation of C-Hal vs. C-H bonds in highly oxidized interme diates towards dissociation, Hal+ ions being much poorer leaving groups than H+. Examples include especially macrocyclic ligands such as the por phyrins [1], Small perchlorinated aromatic ligands were also used to investigate unusual and normally very reactive oxidation states such as Pt(III) [2].Perhalogenated derivatives of the standard adiimine chelate ligands 2,2'-bipyridine (bpy) and 1, 10-phenanthroline (phen) have not yet been systematically studied although the parent com pounds and their organosubstituted derivatives were employed as ligands in arrangements for oxidation catalysis [3]. In particular, (1,10-phenanthroline)copper(I) complexes with their low-lying metal(d)-to-ligand(7r*) charge transfer * R eprint requests to Prof. Dr. W. Kaim.(MLCT) excited states have received wide attention because of their long-standing application in ana lytical chemistry [4] and their more recent uses as "chemical nucleases" in site-specific DNA cleavage [51 and as photoactivated catalysts [6]. The struc tures of such molecules are also of relevance for supramolecular chemistry, e.g. for the synthesis of catenates and knotted molecules [7], for the under standing of the coordination and functioning of cop per centers in proteins [8] and for potential medical applications [9],...

The molecular structure of the highly oxygen-sensitive complex [L 3 Cu I (NCCH 3 )](BF 4 ) (1) reveals approximately symmetrical coordination by the fac-tridentate (tripodal) ligand L 3 ϭ tris(3-isopropyl-4,5-trimethylenepyrazolyl)methane and a rather short Cu I -N(acetonitrile) distance of 1.865(5) Å . In CH 2 Cl 2 at Ϫ78°C the colourless compound reacts with O 2 to yield a labile purple intermediate (λ max 517 nm) Ϫ presumably a peroxodicopper(II) complex Ϫ which decomposes at Ϫ30°C. No such intermediate was observed on reaction of the Cu I complex of bis(2-pyridylmethyl)benzylamine with O 2 at Ϫ80°C. However, an EPR spectrum with g ʈ ϭ 2.17 and gϭ 2.03 without 63,65 Cu hyperfine splitting was observed at low temperatures. Exposure of the precursor 1 to air under ambient conditions yields dinuclear [L 3 Cu II (µ-OH) 2-2 solution. The structure of the hexakis-(dichloromethane) solvate of 2 with CuϪCu and Cu-O distances of 3.055 and 1.94 Å , respectively, is typical for dihydroxo-bridged dicopper compounds with square-pyramidal Cu II configuration (τ ϭ 0.03), adopting an anti arrangement. In agreement with the relatively wide Cu-O-Cu angles of 103.5°an analysis of the temperature dependence of the magnetic susceptibility revealed a rather strong (J ϭ Ϫ633 cm Ϫ1 ) antiparallel spin-spin coupling. The effect is ascribed to the steric bulk of the ligand L 3 .

The diruthenium(2.5) complex [(Me3TACN)Ru(μ‐Cl)3Ru(Me3TACN)]‐(PF6)2, Me3TACN = 1,4,7‐trimethyl‐1,4,7‐triazacyclononane, has been crystallized for structural characterization. The results are reproduced by density functional theory (DFT) calculations and confirm the sensitivity of the central Ru(μ‐Cl)3Ru core to contacts between the Cl bridging atoms and the co‐ligands. The singly occupied MO is characterized as a σ* MO involving the metal dz2 orbitals and a small halide contribution by DFT calculations and EPR.