S. Neeraj

Transformations of low-dimensional zinc phosphates to complex open-framework structures. Part 1: zero-dimensional to one-, two- and three-dimensional structures

Zero-dimensional 4-membered zinc phosphate monomers, [C6N2H18][Zn(HPO4)(H2PO4)2], I, and [C6N4H21][Zn(HPO4)2(H2PO4)], II, transform under simple reaction conditions to one-, two- and three-dimensional structures. Monomer II, on heating with zinc acetate dihydrate (Zn(OAc)2) in aqueous solution, gives a layered phosphate [C6N4H21][NH4][Zn6(PO4)4(HPO4)2]H2O, III. A novel three-dimensional structure [C6N4H21]4[Zn7(PO4)6]3, IV, with channels comprising Zn7O6 clusters is obtained on heating II in water under hydrothermal conditions. The monomer I transforms to a one-dimensional ladder, [C3N2H5][Zn(HPO4)], V, on heating with imidazole and to a three-dimensional structure, [C4N2H12][Zn2(H2O)(PO4)(HPO4)]2, VI, on heating with piperazine under ordinary conditions. I also transforms to a layered zinc phosphate, [C6N2H18][Zn3(H2O)4(HPO4)4], VII, on heating in water. In addition to the monomer, II, compounds III–VI have been obtained for the first time. The structures formed by the transformations of the monomers also exhibit unique structural features. Thus, in the ladder structure, V, the imidazole molecule is linked to the Zn center similar to the phosphate unit in a typical ladder structure, while in the layered phosphate, III, one-dimensional tubules are linked via ZnO4 tetrahedra and the three-dimensional structure, IV, possesses Zn7O6 clusters. Isolation of several related solids encompassing a variety of architectures through the transformations of zero-dimensional monomeric phosphates demonstrates not only that the 4-membered ring is a basic structural building unit in these open-framework materials, but also sheds light on the building-up process involved in their formation.

Transformations of the low-dimensional zinc phosphates to complex open-framework structures. Part 2:one-dimensional ladder to two- and three-dimensional structures

Open-framework zinc phosphates with one-dimensional ladder structures are shown to transform, under simple reaction conditions, to two- and three-dimensional structures. Thus, the one-dimensional ladder, [C6N4H22]0.5[Zn(HPO4)2], I, on heating with piperazine in aqueous solution gives a layer phosphate, [C4N2H12][Zn2(PO4)2], III, and the three-dimensional phosphates [C2N2H10]0.5[Zn(PO4)], IV, [C6N4H22]0.5[Zn2(PO4)2], V and [C6N4H21]4[Zn21(PO4)18], VI. On heating in water in the absence of any amine, I transforms to a three-dimensional solid, [C6N4H22]0.5[Zn3(PO4)2(HPO4)], VII, with 16-membered channels. Of these, III and IV are the only new compounds. The phosphates formed by the transformations of I exhibit unique structural features. Thus, in III, the layers are formed only with 3- and 4-membered rings and have step-like features due to the presence of infinite Zn–O–Zn linkages. Compound IV has a structure similar to that of the naturally occurring aluminosilicate, gismondine, and VI possesses unusual Zn7O6 clusters. The ladder zinc phosphate, [C3N2H12][Zn(HPO4)2], II, transforms to two layered compounds, [C3N2H12][Zn4(PO4)2(HPO4)2], VIII, and [C3N2H12][Zn2(HPO4)3], IX, on heating with zinc acetate and water, respectively. II, on heating in water in the presence of other amines, forms a ladder, [C3N2H5][Zn(HPO4)], X, and a three-dimensional phosphate, [C3N2H12]2[Zn5(H2O)(PO4)4(HPO4)], XI. The syntheses and structures of VIII–XI have already been reported. What is interesting is that the majority of the transformations seem to occur through the process of deprotonation of the phosphoryl group and elimination of the –HPO4 unit. The transformations of the ladder phosphates to higher dimensional structures reported in the present study not only demonstrate the seminal role of the one-dimensional structures as basic building units, but also the likely occurrence of self-assembly of these one-dimensional units in the building-up process.

Amine Phosphates as Intermediates in the Formation of Open‐Framework Structures

Chain, ladder, layer, and three-dimensional metal phosphates were obtained by the reaction of amine phosphates with metal ions under mild hydrothermal conditions. The role of amine phosphates as intermediates in hydrothermal syntheses was corroborated by in situ NMR spectroscopy and X-ray diffraction studies. The picture shows a simple corner-shared linear chain structure formed in the reaction of piperazine phosphate with Zn(II) ions.

An Unusual Open‐Framework Cobalt(II) Phosphate with a Channel Structure That Exhibits Structural and Magnetic Transitions

An Unusual Open-Framework Cobalt(II) Phosphate with a Channel Structure That Exhibits Structural and Magnetic Transitions

Transformations of two-dimensional layered zinc phosphates to three-dimensional and one-dimensional structures

Transformations of the layered zinc phosphates of the compositions [C6N4H22]0.5[Zn2(HPO4)3], I, [C3N2H12][Zn2(HPO4)3], II and [C3N2OH12][Zn2(HPO4)3], III, containing triethylenetetramine, 1,3-diaminopropane, and 1,3-diamino-2-hydroxypropane, respectively, have been investigated under different conditions. On heating in water, I transforms to a one-dimensional (1-D) ladder and a three-dimensional (3-D) structure, while II gives rise to only a two-dimensional (2-D) layered structure. In the transformation reaction of I with zinc acetate, the same ladder and 3-D structures are obtained along with a tubular layer. Under similar conditions II gives a layered structure formed by the joining of two ladder motifs. III, on the other hand, is essentially unreactive when heated with water and zinc acetate, probably because the presence of the hydroxy group in the amine which hydrogen bonds to the framework. In the presence of piperazine, I, II and III give rise to a four-membered, corner-shared linear chain which is likely to be formed via the ladder structure. In addition, 2-D and 3-D structures derived from the 1-D linear chain or ladder structures are also formed. The primary result from the study is that the layers produce 1-D ladders, which then undergo other transformations. It is noteworthy that in the various transformations carried out, most of the products are single-crystalline.

Synthons and design in metal phosphates and oxalates with open architectures

We briefly describe the structures of open-framework metal phosphates with different dimensionalities, such as the one-dimensional linear-chain and ladder structures, two-dimensional layer structures and three-dimensional structures with channels. We demonstrate the role of the zero-dimensional four-membered ring monomer and of the one-dimensional ladder structure as the starting building units or synthons involved in the formation of the complex architectures. Thus, we show how the one-dimensional ladder structure transforms to two- and three-dimensional structures under mild conditions. The two-dimensional layer structures also transform to three-dimensional structures, while the zero-dimensional monomer transforms to layered and three-dimensional structures under ordinary reaction conditions. These transformations provide an insight into the possible pathways involved in the building up of the complex structures of metal phosphates. The isolation of amine phosphates during the hydrothermal synthesis of metal phosphates and also the facile reactions between amine phosphates and metal ions to yield a variety of open-framework materials have thrown light on the mechanism of formation and design of these structures. The existence of a hierarchy of open-framework metal oxalates and their ready formation by employing amine oxalates as intermediates provides additional support to the observations made earlier with regard to the phosphates.

Three-dimensional open-framework CoII and ZnII phosphates synthesized via the amine phosphate route

The reaction of amine phosphates with metal ions, under mild conditions, has been utilized for the synthesis of open-framework phosphates. Two new amine phosphates, DABCO-phosphate and imidazole-phosphate, synthesized for the first time, were employed for this purpose. Thus, DABCO-phosphate reacts with Co(II) and Zn(II) ions giving rise to open-framework structures, of which [C 6 N 2 H 14 ][Co 2 (HPO 4 ) 3 ], I , is a new 3-dimensional structure. Reaction of imidazole phosphate with Zn(II) ions gave a new phosphate, II , [C 3 N 2 H 6 ][Zn 4 (OH)((PO 4 ) 3 ]. Both I and II have linkages involving MO 4 (M=Co, Zn) and PO 4 tetrahedra giving rise to three-dimensional structures. While I has two distinct channels along the crystallographic directions, II possesses only one-dimensional channels along with one-dimensional infinite ZnOZn chains.

One-dimensional zinc phosphates with linear chain structure

Three one-dimensional zinc phosphates, [C5N2H14][Zn(HPO4)2], I, [C10N4H26][Zn(HPO4)2].2H2O II, and [C4N2H6]2[Zn(HPO4)], III, have been prepared employing hydro/solvothermal methods in the presence of organic amines. While I and II consist of linear chains of corner-shared four-membered rings, III is a polymeric wire where the amine molecule is directly bonded to the metal center. The wire, as well as the chain in these structures, are held together by hydrogen bond interactions involving the amine and the framework oxygens. The polymeric zinc phosphate with wire-like architecture, III, is only the second example of such architecture. Crystal data: I, monoclinic, P21/c (no. 14), a=8.603(2), b=13.529(2), c=10.880(1) A, β=94.9(1)°, V=1261.6(1) A3, Z=4, ρcalc.=1.893 gcm−3, μ(MoKα)=2.234 mm−1, R1=0.032, wR2=0.086, [1532 observed reflections with I>2σ(I)], II, orthorhombic, Pbca (no. 61), a=8.393(1), b=15.286(1), c=22.659(1) A, V=2906.9(2) A3, Z=8, ρcalc.=1.794 gcm−3, μ(MoKα)=1.957 mm−1, R1=0.055, wR2=0.11, [1565 observed reflections with I>2σ(I) and III, monoclinic, P21/c (no. 14), a=8.241(1), b=13.750(2), c=10.572(1) A, β=90.9(1)°, V=1197.7(2) A3, Z=4, ρcalc.=1.805 gcm−3, μ(MoKα)=2.197 mm−1, R1=0.036, wR2=0.10, [1423 observed reflections with I>2σ(I)].

Synthesis and structure of an open-framework chlorophosphate, [C6NH14][ZnCl(HPO4)]

A zinc chlorophosphate, of the composition [C6NH14][ZnCl(HPO4)], with a layered architecture has been synthesized, for the first time, in the presence of cyclohexylamine as the structure-directing agent. The structure comprises a network of ZnO3Cl and PO4 tetrahedra forming macroanionic layers with four- and eight-membered apertures. Charge compensation is achieved by the protonated amine occupying inter-lamellar space and interacts with the framework via hydrogen bonding. The crystal structure of the new compound was determined.

A zinc phosphate, [NH3(CH2)3NH3][Zn4(PO4)2(HPO4)2], possessing alternate inorganic and organic layers

Abstract A new zinc phosphate of the formula, [NH 3 (CH 2 ) 3 NH 3 ][Zn 4 (PO 4 ) 2 (HPO 4 ) 2 ], has been synthesized hydrothermally starting from a zinc amine complex. It crystallizes in the monoclinic space group C2/c ; a =17.279(1), b =5.193(1), c =20.115(1) A, β =92.6(1)°; V =1803.1(2) A 3 ; Z =4; D calc =2.05 g cm −3 ; μ (MoKα)=5.62 mm −1 . The final R , and wR 2 =0.037, 0.093 obtained for 136 observed data [I>2 σ (I)]. The structure consists of macroanionic sheets of interconnected ZnO 4 and PO 4 tetrahedra in the ab plane. The sheets are held together by hydrogen bond interactions with the organic structure-directing amine, forming alternate inorganic–organic layers in this material. Hydrogen bond interactions between the inorganic layers, via the terminal –OH group, leads to the formation of pseudo one-dimensional channels.