Di- and Trinuclear Complexes Derived from Hexakis(2-pyridyloxy)cyclotriphosphazene. Unusual P−O Bond Cleavage in the Formation of [{(L‘CuCl)2(Co(NO3)}Cl] (L‘ = N3P3(OC5H4N)5(O))

Effect of pyridyl donors from organic ligands versus metalloligands on material design

This review illustrates designs and structures of various coordination frameworks constructed using assorted organic ligands and metalloligands offering pyridyl donors to evaluate the impact of flexibility versus rigidity on material design.

Silver(I) coordination polymers assembled from flexible cyclotriphosphazene ligand: structures, topologies and investigation of the counteranion effects

The reactions of a flexible ligand hexakis(3-pyridyloxy)cyclotriphosphazene (HPCP) with a variety of silver(I) salts (AgX;X= NO3−, PF6−, ClO4−, CH3PhSO3−, BF4−and CF3SO3−) afforded six silver(I) coordination polymers, namely {[Ag2(HPCP)]·(NO3)2·H2O}n(1), {[Ag2(HPCP)(CH3CN)]·(PF6)2}n(2), {[Ag2(HPCP)(CH3CN)]·(ClO4)2}n(3), [Ag3(HPCP)(CH3PhSO3)3]n(4), [Ag2(HPCP)(CH3CN)(BF4)2]n(5) and {[Ag(HPCP)]·(CF3SO3)}n(6). All of the isolated crystalline compounds were structurally determined by X-ray crystallography. Changing the counteranions in the reactions, which were conducted under similar conditions ofM/Lratio (1:1), temperature and solvent, resulted in structures with different types of topologies. In complexes (1)–(6), the ligand HPCP shows different coordination modes with AgIions giving two-dimensional layered structures and three-dimensional frameworks with different topologies. Complex (1) displays a new three-dimensional framework adopting a (3,3,6)-connected 3-nodal net with point symbol {4.62}2{42.610.83}. Complexes (2) and (3) are isomorphous and have a two-dimensional layered structure showing the same 3,6L60 topology with point symbol {4.26}2{48.66.8}. Complex (4) is a two-dimensional structure incorporating short Ag...Ag argentophilic interactions and has a uninodal 4-connectedsql/Shubnikov tetragonal plane net with {44.62} topology. Complex (5) exhibits a novel three-dimensional framework and more suprisingly contains twofold interpenetrated honeycomb-like networks, in which the single net has a trinodal (2,3,5)-connected 3-nodal net with point symbol {63.86.12}{63}{8}. Complex (6) crystallizes in a trigonal crystal system with the space group R\bar 3 and possesses a three-dimensional polymeric structure showing a binodal (4,6)-connectedfshnet with the point symbol (43.63)2.(46.66.83). The effect of the counteranions on the formation of coordination polymers is discussed in this study.

Molecular, 1D and 2D assemblies from hexakis(3-pyridyloxy)cyclophosphazene containing 20-membered metallamacrocyclic motifs

The coordination behaviour of hexakis(3-pyridyloxy)cyclophosphazene (L) towards divalent metal ions is described. The reaction of L with hydrated metal nitrates afforded [{N3P3(O-C5H4N-3)6}2{Zn(H2O)3(NO3)}2{Zn(H2O)2(NO3)}2]n[NO3]2n·4nH2O·nCH3OH (1), [{N3P3(O-C5H4N-3)6}2{Zn(H2O)3(NO3)}2{Cu(NO3)}2]n[NO3]2n·4nH2O·nCH3CN (2), [{N3P3(O-C5H4N-3)6}2{(NO3)Cd-(μ-(NO3)-Cd(NO3)2(μ-(NO3)Cd(NO3)}]n·2nCH3OH·3nH2O (3), and [{N3P3(O-C5H4N-3)6}2{Cd(H2O)3(NO3)}2][NO3]2·9H2O (4). 1 and 2 are one-dimensional coordination polymers while 3 is a two-dimensional coordination polymer. On the other hand 4 is a molecular metallamacrocycle. A common feature of 1-4 is the presence of a 20-membered dimetallamacrocyclic motif constructed through the involvement of a pair of cyclophosphazene ligands through their geminal pyridyloxy substituents. The P-N bond distances in L and its metal complexes 1-4 are nearly the same indicating the flexible nature of the coordination pyridyloxy arms present on the cyclophosphazene scaffold.

Reactions of alkyne- and butadiyne-derived fluorinated cyclophosphazenes with diiron and dimolybdenum carbonyls

The reaction of (β-phenylethynyl)pentafluorocyclotriphosphazene, [(PhC≡C)(F)PN](PNF2)2, with Fe2(CO)9 in refluxing hexane resulted in five new compounds, namely, [Fe(CO)2{η(2):η(2)-2,4-(P3N3F5)2Ph2C4Fe(CO)3}-μ-CO] (1), [Fe(CO)2{η(2):η(2)-2,5-(P3N3F5)2Ph2C4Fe(CO)3}-μ-CO] (2), [Fe(CO)2{η(5)-2,5-(P3N3F5)2Ph2C4CO}C(Ph)═C(P3N3F5)](3), [Fe(CO)3{η(2):η(2)-2,4-(P3N3F5)2Ph2C4CO] (4), and [Fe(CO)3{η(2):η(2)-2,5-(P3N3F5)2Ph2C4CO] (5). While compounds 1, 2, 4, and 5 have five-membered ferracyclopentadiene or cyclopentadienone rings coordinated to the Fe(CO)3 unit in the η(2):η(2) mode, compound 3 has a 2,5-cyclopentadienone ring attached to an Fe(CO)2(P3N3F5)C═C(Ph) unit, where Fe is η(5)-bonded to the cyclopentadienone ring, and the carbon that is α to the phenyl unit of the Fe(CO)2(P3N3F5)C═C(Ph) group is σ-bonded to the oxygen atom of the cyclopentadienone ring. Formation of five-membered cyclic compounds having two fluorophosphazene units on the vicinal carbon atoms of C4R2R'2Y rings was not observed in this reaction. No examples of Fe(CO)3-bound cyclobutadiene complexes were also isolated from this reaction. A similar reaction in the presence of trimethylamine N-oxide, NMe3O, was found to proceed at -20 °C with the formation of compounds 4 and 5 only. In contrast to the Fe2(CO)9 reaction, a reaction of alkyne-derived pentafluorocyclotriphosphazenes, [(RC≡C)(F)PN](PNF2)2 [R = Ph, Fe(C5H5)2] with the molybdenum complex Cp(CO)3Mo-Mo(CO)3Cp (Cp = cyclopentadienyl) in refluxing toluene resulted in the simple tetrahedral clusters Cp(CO)2Mo(P3N3F5)C-C(Ph)Mo(CO)2Cp (6) and Cp(CO)2Mo(P3N3F5)C-C(Fc)Mo(CO)2Cp (7) (Fc = ferrocenyl). A similar reaction of Cp(CO)3Mo-Mo(CO)3Cp with butadiyne-derived fluorophosphazenes, [(RC≡C-C≡C)(F)PN](PNF2)2 [R = Ph, Fe(C5H5)2], yielded the tetrahedral clusters Cp(CO)2Mo(P3N3F5)C-C(C≡CPh)Mo(CO)2Cp (8) and Cp(CO)2Mo(P3N3F5)C-C(C≡CFc)Mo(CO)2Cp (9) with the tetrahedral Mo2C2 unit forming exclusively with the alkyne unit of the butadiyne group bound to the cyclophosphazene ring. The crystal structures and infrared spectral data of these molybdenum clusters showed the presence of a semibridging carbonyl on one of the molybdenum units. All new compounds were characterized by IR, NMR [(1)H, (13)C{(1)H}, (31)P{(1)H}, and (19)F{(1)H}] and high-resolution mass spectrometry studies. Compounds 2, 3, 5, and 7-9 were also structurally characterized using single-crystal X-ray diffraction studies.

Chiral multidentate oxazoline ligands based on cyclophosphazene cores: synthesis, characterization and complexation studies

Chiral oxazoline derivatives of cyclophosphazenes were prepared and their complexation and catalytic studies for the asymmetric rearrangement of trichloroacetimidates to trichloroacetamides have been performed.

Cyclophosphazene–organostannoxane hybrid motifs in polymeric and molecular systems

The synthesis and structural characterization of two hybrid inorganic ring systems that contain interconnected cyclophosphazene–stannoxane motifs are reported.

Enantiomeric specificity of biologically significant Cu(II) and Zn(II) chromone complexes towards DNA

Novel chiral Schiff base ligands (R)/(S)-2-amino-3-(((1-hydroxypropan-2-yl)imino)methyl)-4H-chromen-4-one (L(1) and L(2)) derived from 2-amino-3-formylchromone and (R/S)-2-amino-1-propanol and their Cu(II)/Zn(II) complexes (R1, S1, R2, and S2) were synthesized. The complexes were characterized by elemental analysis, infrared (IR), hydrogen ((1) H) and carbon ((13)C) nuclear magnetic resonance (NMR), electrospray ionization-mass spectra (ESI-MS), and molar conductance measurements. The DNA binding studies of the complexes with calf thymus were carried out by employing different biophysical methods and molecular docking studies that revealed that complexes R1 and S1 prefers the guanine-cytosine-rich region, whereas R2 and prefers the adenine-thymine residues in the major groove of DNA. The relative trend in K(b) values followed the order R1>S1>R2>S2. This observation together with the findings of circular dichroic and fluorescence studies revealed maximal potential of (R)-enantiomeric form of complexes to bind DNA. Furthermore, the absorption studies with mononucleotides were also monitored to examine the base-specific interactions of the complexes that revealed a higher propensity of Cu(II) complexes for guanosine-5'-monophosphate disodium salt, whereas Zn(II) complexes preferentially bind to thymidine-5'-monophosphate disodium salt. The cleavage activity of R1 and R2 with pBR322 plasmid DNA was examined by gel electrophoresis that revealed that they are good DNA cleavage agents; nevertheless, R1 proved to show better DNA cleavage ability. Topoisomerase II inhibitory activity of complex R1 revealed that the complex inhibits topoisomerase II catalytic activity at a very low concentration (25 μM). Furthermore, in vitro antitumor activity of complexes R1 and S1 were screened against human carcinoma cell lines of different histological origin.

Synthesis of new heterometallic macromolecules: their DNA binding, cleavage activity and in vitro model electrochemotherapy study

The homodinuclear C(16)H(30)N(8)O(5)Sn(2)Cl(4) (1), heterotetranuclear C(16)H(38)N(8)O(9)Sn(2)Cu(2)Cl(8) (2) and C(16)H(38)N(8)O(9)Sn(2)Mn(2)Cl(8) (3) macrocyclic complexes were synthesized and characterized by elemental analysis, spectroscopic techniques and molar conductance measurements. The interaction studies of 1-3 with calf thymus DNA (CT-DNA) were carried out by UV-vis titration, fluorescence, cyclic voltammetry and viscosity measurements. These results were further authenticated by carrying out interaction studies of 1-3 with plasmid pBR322 DNA employing gel electrophoresis. To overcome the dose resistance, auto toxicity of the drugs, a model study based on electrochemotherapy (ECT) was carried out and the results were compared in the presence and in the absence of the applied electrical potential.

Phosphorus-supported ligands for the assembly of multimetal architectures

Modeled after boron-based scorpionate ligands, acyclic and cyclic phosphorus-containing compounds possessing reactive groups can serve as excellent precursors for the assembly of novel phosphorus-supported ligands that can coordinate multiple sites. In such ligands, the phosphorus atom does not have any role in coordination but is used as a structural support to assemble one or more coordination platforms. In this Account, we describe the utility of inorganic heterocyclic rings such as cyclophosphazenes and carbophosphazenes as well as acyclic phosphorus-containing compounds such as (S)PCl(3), RP(O)Cl(2), and R(2)P(O)Cl for building such multisite coordination platforms. We can modulate the number and orientation of such coordination platforms through the choice of the phosphorus-containing precursor. This methodology is quite general and modular and allows the creation of well-defined libraries of multisite coordination ligands. Phosphorus-supported pyrazolyl ligands are quite useful for building multimetallic architectures. Some of these ligands are prone to P-N bond hydrolysis upon metalation, but we have exploited the P-N bond sensitivity to generate hydrolyzed ligands in situ, which are useful to build multimetal assemblies. In addition, the intimate relationship between small molecule cyclophosphazenes and the corresponding pendant cyclophosphazene-containing polymer systems facilitated our design of polymer-supported catalysts for phosphate ester hydrolysis, plasmid DNA modification, and C-C bond formation reactions. Phosphorus hydrazides containing reactive amine groups are ideal precursors for integration into more complex ligand systems. The ligand (S)P[N(Me)N=CH-C(6)H(4)-2-OH](3) (LH(3)) contains six coordination sites, and its coordination response depends upon the oxidation state of the metal ion employed. LH(3) reacts with divalent transition metal ions to afford neutral trimetallic derivatives L(2)M(3), where the three metal ions are arranged in a perfectly linear manner in many cases. Incorporating an additional methoxy group into LH(3) affords the ligand (S)P[N(Me)N=CH-C(6)H(3)-2-OH-3-OMe](3) (L'H(3)), which contains nine coordination sites: three imino nitrogen atoms, three phenolate oxygen atoms, and three methoxy oxygen atoms. The reaction of L'H(3) with transition metal salts in 1:1 ratio leads to the in situ formation of a metalloligand (L'M), which on further treatment with lanthanide salts gives heterobimetallic trinuclear cationic complexes [L'(2)M(2)Ln](+) containing a M-Ln-M linear array (M = transition metal ion in a +2 oxidation state). Many of these 3d-4f compounds behave as single-molecule magnets at low temperatures. Although challenges remain in the development of synthetic methods and in the architectural control of the coordination platforms, we see opportunities for further research into coordination platforms supported by main group elements such as phosphorus. As we have shown in this Account, one potential disadvantage, sensitivity of P-N bonds to hydrolysis, can be used successfully to build larger assemblies.