Extracting structural trends from systematic variation of phosphonate/phosphonate monoester coordination polymers

Systematic variation of ligand geometry and ester size shows that dimensionality of barium phosphonate/phosphonate ester structures can be truncated by either route.

Dimensionality Alteration and Intra- versus Inter-SBU Void Encapsulation in Zinc Phosphate Frameworks

4,4'-Bipyridine-N-oxide (BIPYMO, 1), a less commonly employed coordination polymer linker, has been used as a ditopic spacer to bridge double-four-ring (D4R) zinc phosphate clusters to form novel framework coordination polymers. Zinc phosphate framework compounds [Zn4(X-dipp)4(BIPYMO)2]n·2MeOH [X = H (2), Cl (3), Br (4), I (5); dipp = 2,6-diisopropylphenyl phosphate] have been obtained by treating a methanol solution of zinc acetate with X-dippH2 and BIPYMO (in a 1:1:1 molar ratio) at ambient conditions. Framework phosphates 2-5 can also be obtained by treating the preformed D4R cubanes [Zn(X-dipp)(DMSO)]4 with required quantities of BIPYMO in methanol. Single-crystal X-ray diffraction studies reveal that these framework solids are two-dimensional (2D) networks as opposed to the diamondoid networks obtained when the parent unoxidized 4,4'-bipyridine is used as the linker (Inorg. Chem. 2014, 53, 8959). The two types of voids (viz., smaller intra-D4R and larger inter-D4R) present in these framework solids can be utilized for different types of encapsulation processes. For example, the in situ generated 2D framework 2 encapsulates fluoride ions accompanied by a change in the dimensionality of the framework to yield {[(nC4H9)4N][F@(Zn4(dipp)4(BIPYMO)2)]}n (6). The three-dimensional framework 6 represents the first structurally characterized example of a fluoride-ion-encapsulated polymeric coordination compound or a metal-organic framework. The possibility of utilizing inter-D4R voids as hosts for small organic molecules has been explored by treating in situ generated 2 with a series of organic molecules of appropriate size. Framework 2 has been found to be a selective host for benzil and not for other structurally similar molecules such as benzoquinone, benzidine, anthracene, naphthalene, α-pyridoin, etc. The benzil-occluded isolated framework [benzil@{Zn4(dipp)4(BIPYMO)2}]n (7) has been isolated as single crystals, and its crystal structure determination revealed the binding of benzil molecules to the framework through strong π-π interactions.

Alkylzinc diorganophosphates: synthesis, structural diversity and unique ability to incorporate zincoxane units

New tetrameric alkylzinc organophosphates of a drum-like structure and novel aggregates based on alkylzinc organophosphates with incorporated zincoxane units were synthesized and structurally characterized.

Octanuclear zinc phosphates with hitherto unknown cluster architectures: ancillary ligand and solvent assisted structural transformations thereof

Structural variations in zinc phosphate cluster chemistry have been achieved through a careful selection of phosphate ligand, ancillary ligand, and solvent medium. The use of 4-haloaryl phosphates (X-dippH2) as phosphate source in conjunction with 2-hydroxypyridine (hpy) ancillary ligand in acetonitrile solvent resulted in the isolation of the first examples of octameric zinc phosphates [Zn8(X-dipp)8(hpy)4(CH3CN)2(H2O)2]·4H2O (X = Cl 2, Br 3) and not the expected tetranuclear D4R cubane clusters. Use of 2,3-dihydroxypyridine (dhpy) as ancillary ligand, under otherwise similar reaction conditions with the same set of phosphate ligands and solvent, resulted in isolation of another type of octanuclear zinc phosphate clusters {[(Zn8(X-dipp)4(X-dippH)4(dhpyH)4(dhpyH2)2(H2O)2]·2solvent} (X = Cl, solvent = MeCN 4; Br, solvent = H2O 5), as the only isolated products. X-ray crystal diffraction studies reveal that 2 and 3 are octanuclear clusters that are essentially formed by edge fusion of two D4R zinc phosphates. Although 4 and 5 are also octanuclear clusters, they exhibit a completely different cluster architecture and have been presumably formed by the ability of 2,3-dihydroxypyridine to bridge zinc centers in addition to the X-dipp ligands. Dissolution of both types of octanuclear clusters in DMSO followed by crystallization yields D4R cubanes [Zn(X-dipp)(DMSO)]4 (X = Cl 6, Br 7), in which the ancillary ligands such as hpy, H2O, and CH3CN originally present on the zinc centers of 2-5 have been replaced by DMSO. DFT calculations carried out to understand the preference of Zn8 versus Zn4 clusters in different solvent media reveal that use of CH3CN as solvent favors the formation of fused cubanes of the type 2 and 3, whereas use of DMSO as the solvent medium promotes the formation of D4R structures of the type 6 and 7. The calculations also reveal that the vacant exocluster coordination sites on the zinc centers at the bridgehead positions prefer coordination by water to hpy or CH3CN. Interestingly, the initially inaccessible D4R cubanes [Zn(X-dipp)(hpy)]4·2MeCN (X = Cl 8, Br 9) could be isolated as the sole products from the corresponding DMSO-decorated cubanes 6 and 7 by combining them with hpy in CH3CN.

Is single-4-ring the most basic but elusive secondary building unit that transforms to larger structures in zinc phosphate chemistry?

Haloaryl phosphates (X-dippH2, X = Cl, Br, I) react with zinc acetate in the presence of collidine or 2-aminopyridine (2-apy) to yield zinc phosphate clusters [Zn(X-dipp)(collidine)]4 (X = Cl (1), Br (2), I (3)) and [Zn(X-dipp)(2-apy)]4·2MeOH (X = Cl (4), Br (5), I (6)), respectively. Single-crystal X-ray diffraction studies reveal that collidine and 2-apy capped zinc phosphates 1-6 exist as discrete tetrameric zinc phosphate molecules, exhibiting a cubane-shaped D4R core. In contrast, when the same reaction has been carried out in the presence of 4-cyanopyridine (4-CNpy), polymeric zinc phosphates {[Zn4(X-dipp)4(4-CNpy)2(MeOH)2]·2H2O}n (X = Cl (7), Br (8), I (9)) have been isolated. Compounds 7-9 are square-wave-shaped, one-dimensional polymers composed of fused S4R repeating units. The common structural motif found both in D4R cubanes 1-6 and polymers 7-9 is the S4R building block, which presumably undergoes further fusion because of the coordinative unsaturation at zinc and the simultaneous presence of free P═O. The closed shell cubanes 1-6 are obviously formed by a face-to-face dimerization involving two S4R units in which the two P═O groups are in cis-configuration. On the other hand, the one-dimensional (1-D) square-wave polymers 7-9 are formed from a face-to-face association of S4R building units in which the two P═O groups are in a trans-configuration. In order to stabilize these elusive S4R zinc phosphates, the reaction between Cl-dippH2 and zinc acetate was carried out in the presence of excess imidazole as an ancillary ligand (1:1:4), although only an imidazole decorated cubane cluster [Zn(Cl-dipp)(imz)]4.2MeOH (10) was isolated. The chelating N,N'-donor 1,10-phenanthroline ligand was used to eventually isolate cyclic S4R phosphate [Zn(μ2-Cl-dipp)(1,10-phen)(OH2)]2·MeOH·H2O (11). The change of Zn(2+) source to zinc nitrate and the phosphate source to 2,6-dimethylphenyl phosphate (dmppH2) led to the isolation of another polymeric phosphate [Zn(dmpp)(MeOH)]n (12), with a zigzag backbone, formed through an edge-to-edge to polymerization of S4R building units with P═O groups in trans-configuration. The isolation of four different structural types of zinc phosphates A-D in the present study can be rationalized in terms of fusion of S4R rings in a variety of ways to either produce discrete clusters or 1-D polymers.

Synthetic strategies to achieve further-functionalised monoaryl phosphate primary building units: crystal structures and solid-state aggregation behavior

The synthesis of a new class of functionalized organophosphates, potential building units in materials and zeolite chemistry, has been reported.

Role of 4,4′-bipyridine versus longer spacers 4,4′-azobipyridine, 1,2-bis(4-pyridyl)ethylene, and 1,2-bis(pyridin-3-ylmethylene)hydrazine in the formation of thermally labile metallophosphate coordination polymers

Uncoordinated N-donors spacers in the title compounds facilitate interesting orthogonal H-bonding, leading to the formation of 3-D polymeric networks.

Discrete {GdIII4M} (M = GdIII or CoII) pentanuclear complexes: a new class of metal-organophosphate molecular coolers

A higher magnetic entropy change is observed for the homometallic {Gd^III₅} complex (25.8 J kg⁻¹ K⁻¹) as compared to the heterometallic {Gd^III₄Co^II} complex (20.3 J kg⁻¹ K⁻¹).

Discrete and polymeric cobalt organophosphates: isolation of a 3-D cobalt phosphate framework exhibiting selective CO2 capture

Auxiliary ligand assisted control over the structural diversity has been achieved in the case of cobalt(ii) organophosphates.