Three-dimensional frameworks built from piperazine-2,5-dione and simple metal salts (M = Co, Ni, Cu and Ag)

Compounds trans-tetra­aqua­dichloridocobalt(II)–piperazine-2,5-dione (1/1), [CoCl₂(H₂O)₄]·C₄H₆N₂O₂, (I), and trans-tetra­aqua­dichloridonickel(II)–piperazine-2,5-dione (1/1), [NiCl₂(H₂O)₄]·C₄H₆N₂O₂, (II), are isomorphous. In each structure, the metal complex and the piperazinedione unit both lie across centres of inversion in the space group P2₁/n. The [MCl₂(H₂O)₄] units (M = Co or Ni) are linked by O—H...Cl hydrogen bonds into sheets of R₂²(8) and R₄²(12) rings, and these sheets are linked by the piperazinedione components via a combination of O—H...O and N—H...Cl hydrogen bonds into a three-dimensional framework. In catena-poly[[[trans-diaqua­copper(II)]-di-μ-chlorido] piperazine-2,5-dione sol­vate], {[CuCl₂(H₂O)₂]·C₄H₆N₂O₂}_n, (III), the metal ion and the piperazine unit both lie across centres of inversion in the space group I2/a. The coordination polymer forms chains of centrosymmetric [CuCl₂(H₂O)₂] units running parallel to [010] and these are linked by the piperazinedione units into a three-dimensional framework structure. In poly[μ₃-nitrato-μ₂-piperazine-2,5-dione-silver(I)], [Ag(NO₃)(C₄H₆N₂O₂)]_n, (IV), the silver and nitrate ions lie on mirror planes in the space group Pnma, while the piperazinedione unit lies across a centre of inversion. The compound is a coordination polymer containing five-coordinate approximately square-pyramidal Ag, in which the ligating O atoms are derived from three different nitrate ligands and two different piperazinedione ligands. The ionic components form sheets in which each anion is coordinated to three different cations, and these sheets are linked into a three-dimensional framework by the organic ligands, each of which coordinates to two different Ag centres. The significance of this study lies in its demonstration of a wide variety of framework types built from a common and very simple organic component with simple metal salts.

S1. Comment

In the structure of piperazine-2,5-dione (diketopiperazine, the cyclic anhydride derived from glycine), the molecules lie across centres of inversion. They are linked into chains of R₂²(8) rings (Bernstein et al., 1995) by means of N—H···O hydrogen bonds (Degeilh & Marsh, 1959; Sarangarajan et al., 2005), and these chains are themselves linked into sheets by C—H···O hydrogen bonds (Sarangarajan et al., 2005). In the hydrogen-bonded adducts formed by piperazine-2,5-dione with simple monocarboxylic acids, the same chain of R₂²(8) rings occurs, with the acid units pendant from it (Kartha et al., 1981; Luo & Palmore, 2002), while with dicarboxylic acids or phenolic monocarboxyic acids these chains are linked into sheets (Luo & Palmore, 2002; Sarangarajan et al., 2005). Unusually, the adduct formed with salicylic acid contains neither chains nor sheets but finite centrosymmetric aggregates of two acid molecules and one piperazinedione unit (Varughese & Kartha, 1982). Despite the substantial number of hydrogen-bonded adducts formed with organic acids, very little structural information is available for metal complexes of piperazine-2,5-dione. However, the closely-related 1,4-dimethylpiperazine-2,5-dione forms a finite encapsulation complex with aluminium tris(2,6-diphenylphenoxide (Ooi et al., 1998), and the same amide forms a one-dimensional coordination polymer with Ph₂SnCl₂ (Kovala-Demertzi et al., 1995). We report here the structures of four adducts, (I)–(IV) (Figs. 1–4), formed by piperazine-2.5-dione when it is co-crystallized from aqueous solutions containing simple salts of Co^II, Ni^II, Cu^II and Ag^I.

Compounds (I) and (II) are isomorphous. In these structures, the metal atom lies at a centre of inversion in space group P2₁/n, selected as that at (1/2, 1/2, 1/2), and it is coordinated by two Cl and four water ligands. Within the selected asymmetric unit, the centrosymmetric piperidinedione component is linked to the neutral [M(H₂O)₄)Cl₂] unit (M = Co or Ni) by a combination of O—H···O and N—H···Cl hydrogen bonds (Table 3), such that the organic component lies across the centre of inversion at (1/2, 0, 0) (Figs. 1 and 2). In each complex, the coordination of the metal atom has symmetry very close to D_4h (4/mmm), with the bond angles subtended at the metal atoms by pairs of cis ligands all within 3° of 90°. The M—O and M—Cl distances are slightly smaller in (II) than in (I) (Table 1).

All of the O—H and N—H bonds within the structures of (I) and (II) are involved in hydrogen bonding (Table 3) and the components are thereby linked into a three-dimensional framework structure. The [M(H₂O)₄)Cl₂] units are linked by the two independent O—H···Cl hydrogen bonds into a sheet parallel to (101) and containing both R₂²(8) and R₄²(12) rings (Fig. 5), and these inorganic sheets then linked by the organic components. This linking is most simply envisaged in terms of a chain running parallel to the [011] direction and containing alternating inorganic and organic units linked by hydrogen-bonded R₂²(8) rings (Fig. 6). The combination of (101) sheets and [011] chains suffices to generate the three-dimensional pillared layer structure, which could be regarded as an organic–inorganic hybrid structure. In nickel(II) chloride tetrahydrate, there are discrete [Ni(H₂O)₄)Cl₂] units, but of cis configuration and lying in general positions. These units are linked into a complex three-dimensional framework structure by both O—H···Cl and O—H···O hydrogen bonds (Ptasiewicz-Bak et al., 1999), so that the hydrogen-bonded structure in the free hydrated chloride is quite different from that found here for the piperazinedione adduct (II).

In the Cu complex, (III), the metal atom lies on a centre of inversion in space group I2/a, selected as that at (1/4, 1/4, 1/4). It is coordinated by two water ligands and by four Cl ligands, each of which bridges two metal centres, so generating a chain of edge-fused octahedra of composition [CuCl₂(H₂O)₂]_n running parallel to the [010] direction (Fig. 3). The piperazinedione component also lies across a centre of inversion, selected as that at (1/2, 1, 1/2), so that within the selected asymmetric unit the components are linked by O—H···O and N—H···Cl hydrogen bonds (Table 3), as in compounds (I) and (II). Within the coordination polymer chain, the centrosymmetric Cu₂Cl₂ units contain two significantly different Cu—Cl distances (Table 1). A similar chain, with Cu—Cl distances of 2.2724 (13) and 3.1537 (14) Å, is present in benzimidazolium tetrachorocuprate [tetrachloridocuprate ?] monohydrate [Cambridge Structural Database (Allen, 2002) refcode FUTRUH; Bukowska-Strzyżewska & Skoweranda, 1987]. More frequently, however, [CuCl₂(H₂O)₂] units are found as isolated square-planar units, as in NPYOCU (Williams et al., 1971) and TPPOCU (Dunaj-Jurco et al., 1979) or as square-planar units weakly coordinated by two further axial ligands, as in UGAYUW (Giantsidis et al., 2002). The hydrogen bonds in (III) link the reference Cu atom at (1/4, 1/4, 1/4), via the piperazinedione units centred at (0, 0, 1/2), (0, -1/2, 0), (1/2, 1/2, 0) and (1/2, 1, 1/2), respectively, to the Cu atoms at (-1/4, -1/4, 3/4), (-1/4, -5/4, -1/4), (3/4, 3/4, -1/4) and (3/4, 7/4, 3/4), so forming a sheet parallel to (211) (Fig. 7). In this manner, the reference coordination polymer chain along (1/4, y, 1/4), is directly linked to the four chains along (-1/4, y, -1/4), (-1/4, y, 3/4), (3/4, y, -1/4) and (3/4, y, 3/4), thereby generating a three-dimensional framework structure.

Complex (IV), derived from Ag[NO₃], is a coordination polymer, [(DKP)Ag(NO₃)]_n [DKP is diketopiperazine?], containing five-coordinate Ag. The compound crystallizes in space group Pnma, and the Ag⁺ ions and all the atoms of the nitrate anions lie on mirror planes, while the DKP units lie across centres of inversion. For the selected asymmetric unit, in which DKP atom O12 is coordinated to Ag (Fig. 4), the DKP unit lies across the centre of inversion at (1/2, 1/2, 0), while the Ag⁺ and nitrate ions lie on the mirror plane at y = 1/4. The constitution of (IV) is most readily analysed in terms of the two-dimensional sub-structure built from Ag and [NO₃] units only. These layers are linked by the DKP units acting as bridging ligands between pairs of Ag ions in different layers. Within the ionic layer, the Ag⁺ ion at (x, 1/4, z) is coordinated by O atoms from three different nitrate ions, namely atom O1 in the anion at (x, 1/4, z), atom O2 in the anion at (x, 1/4, -1 + z) and atom O3 in the anion at (-1/2 + x, 1/4, 3/2 - z) (Table 2). Propagation of these interactions then leads to the formation of an (010) sheet built from a single type of 12-membered ring (Fig. 8).

In addition to the three O ligands from within the ionic layer, the Ag⁺ ion at (x, 1/4, z) is also coordinated by two O atoms from two different DKP ligands, namely those at (x, y, z) and (x, 1/2 - y, z). The coordination polyhedron around the Ag⁺ ion is best described as a distorted square pyramid (Fig. 4) in which two of the basal Ag—O distances are significantly longer than the other pair (Table 2). The two independent O—Ag—O angles in the basal plane have values close to 90°, while the angles subtended at Ag by the axial O and one of the basal O sites range from 74.94 (6) to 114.11 (6)°. The atoms of type O12 at (x, y, z) and (x, 1/2 - y, z) form part of the DKP units centred at (1/2, 1/2, 0) and (1/2, 0, 0), respectively, so that propagation of this Ag—O interaction by reflection and inversion generates a chain running parallel to the [010] direction (Fig. 9) which serves to link all of the (010) layers into a three-dimensional coordination polymer. The three-dimensional framework is reinforced by a single N—H···O hydrogen bond.

Thus, in each of compounds (I) and (II) there is a finite [M(H₂O)₄Cl₂] fragment, in compound (III) there is a one-dimensional coordination polymer, [CuCl₂(H₂O)₂]_n, and in compound (IV) there is a three-dimensional coordination polymer, [Ag(NO₃)(C₄H₆N₂O₂]_n. In (I) and (II), the formation of the three-dimensional framework is dependent upon the actions of multiple hydrogen bonds, while in compound (IV) the framework is formed by the three-dimensional coordination polymer, to the formation of which the single hydrogen bond is incidental. The three-dimensional framework in (III) is of a hybrid type, depending upon hydrogen bonds to link the one-dimensional coordination polymer chains. The organic piperazine-2,5-dione component may thus prove to be a very versatile building block for crystal structure design and construction.

S2. Experimental

Compounds (I)–(IV) were prepared by dissolving in water equimolar quantities of piperazine-2,5-dione and, respectively, cobalt(II) chloride hexahydrate, nickel(II) chloride tetrahydrate, copper(II) chloride dihydrate or silver nitrate. The solutions were set aside to crystallize, providing crystals of (I)–(IV) suitable for single-crystal X-ray diffraction.

S3. Refinement

For compounds (I), (II) and (IV, the space groups were uniquely assigned from the systematic absences as P2₁/n, P2₁/n and Pnma, respectively. For compound (III), the systematic absences permitted Cc and C2/c as possible space groups; C2/c was selected and confirmed by the refinement. Because of the very large value of β in C2/c [132.180 (3)°], the alternative setting I2/a was adopted prior to the final refinement. Compound (III) was refined as a non-merohedral twin, resulting in twin fractions of 0.469 and 0.531.

For each of (I)–(IV), all H atoms were located in difference maps and then treated as riding atoms, with C—H = 0.99, N—H = 0.88 and O—H = 0.84 or 0.90 Å, and with U_iso(H) = 1.2U_eq(C,N) or 1.5U_eq(O).

Computing details

For all compounds, data collection: KappaCCD Server Software (Nonius, 1997); cell refinement: DENZO-SMN (Otwinowski & Minor, 1997); data reduction: DENZO-SMN (Otwinowski & Minor, 1997); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: PLATON (Spek, 2003); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008) and PRPKAPPA (Ferguson, 1999).

Figures

	Fig. 1. The independent molecular components in (I), showing the atom-labelling scheme and the hydrogen bonds within the selected asymmetric unit (dashed lines). Displacement ellipsoids are drawn at the ??% probability level [Please complete] and H atoms are shown as small spheres of arbitrary radii. [Symmetry codes: (i) 1 - x, 1 - y, 1 - z; (ii) 1 - x, -y, -z.]
	Fig. 2. The independent molecular components in (II), showing the atom-labelling scheme and the hydrogen bonds within the selected asymmetric unit (dashed lines). Displacement ellipsoids are drawn at the ??% probability level [Please complete] and H atoms are shown as small spheres of arbitrary radii. [Symmetry codes: (i) 1 - x, 1 - y, 1 - z; (ii) 1 - x, -y, -z.]
	Fig. 3. The independent components in (III), showing the atom-labelling scheme together with a portion of the [CuCl2(H2O)2]n coordination polymer. Displacement ellipsoids are drawn at the 30% probabiility level and H atoms are shown as small spheres of arbitrary radii. [Symmetry codes: (i) x, -1 + y, z; (ii) x, 1 + y, z; (iii) 1/2 - x, 1/2 - y, 1/2 - z; (iv) 1/2 - x, 3/2 - y, 1/2 - z; (v) 1 - x, 2 - y, 1 - z; (vi) 1/2 - x, -1/2 - y, 1/2 - z.]
	Fig. 4. The independent components of adduct (IV), showing the atom-labelling scheme and the five-coordination of the Ag. Displacement ellipsoids are drawn at the 30% probability level and H atoms are shown as small spheres of arbitrary radii. [Symmetry codes: (i) x, 1/4, -1 + z); (ii) -1/2 + x, 1/4, 3/2 - z); (iii) 1 - x, 1 - y, -z; (iv) x, 1/2 - y, z.]
	Fig. 5. A stereoview of part of the crystal structure of (I), showing the formation of a hydrogen-bonded sheet built from [Co(H2O)4)Cl2] units only.
	Fig. 6. A stereoview of part of the crystal structure of (I), showing the formation of a hydrogen-bonded chain built from alternating [Co(H2O)4)Cl2] and piperazinedione units. For the sake of clarity, H atoms bonded to C atoms have been omitted.
	Fig. 7. A stereoview of part of the crystal structure of (III), showing the formation of a hydrogen-bonded sheet parallel to (211) formed from [CuCl2(H2O)2] and piperazinedione units.
	Fig. 8. Part of the crystal structure of (IV), showing the formation of a layer parallel to (010) built from silver and nitrate ions only.
	Fig. 9. Part of the crystal structure of (IV), showing the formation of a chain parallel to [010] consisting of cations and DKP units only. For the sake of clarity, H atoms bonded to C atoms have been omitted. Atoms marked with an asterisk (*), a hash (#), a dollar sign ($) or an ampersand (&) are at the symmetry positions (1 - x, 1 - y, -z), (x, 1/2 - y, z), (x, 3/4, z) and (1 - x, 1/2 + y, z), respectively.

(I) trans-Tetraaquadichloridocobalt(II)–piperazine-2,5-dione (1/1)

Crystal data

[CoCl2(H2O)4]·C4H6N2O2	F(000) = 322
Mr = 316.00	Dx = 1.809 Mg m^−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2yn	Cell parameters from 1330 reflections
a = 9.5326 (4) Å	θ = 3.8–27.5°
b = 6.6602 (2) Å	µ = 1.95 mm^−1
c = 10.0167 (4) Å	T = 120 K
β = 114.1660 (17)°	Plate, colourless
V = 580.22 (4) Å^3	0.40 × 0.20 × 0.07 mm
Z = 2

Data collection

Nonius KappaCCD diffractometer	1330 independent reflections
Radiation source: Bruker Nonius FR591 rotating anode	1189 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.032
Detector resolution: 9.091 pixels mm^-1	θmax = 27.5°, θmin = 3.8°
ϕ and ω scans	h = −12→12
Absorption correction: multi-scan (SADABS; Sheldrick, 2003)	k = −8→8
Tmin = 0.509, Tmax = 0.876	l = −12→13
7527 measured reflections

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.021	H-atom parameters constrained
wR(F^2) = 0.053	w = 1/[σ^2(Fo^2) + (0.020P)^2 + 0.3391P] where P = (Fo^2 + 2Fc^2)/3
S = 1.05	(Δ/σ)max < 0.001
1330 reflections	Δρmax = 0.44 e Å^−3
71 parameters	Δρmin = −0.37 e Å^−3
0 restraints	Extinction correction: SHELXL97 (Sheldrick, 2008), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.0182 (19)

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
Co1	0.5000	0.5000	0.5000	0.00843 (11)
Cl1	0.36781 (4)	0.51301 (5)	0.23198 (4)	0.01167 (11)
O1	0.59489 (11)	0.22731 (14)	0.49628 (11)	0.0148 (2)
O2	0.68877 (11)	0.65237 (14)	0.48809 (10)	0.0129 (2)
O12	0.60342 (13)	−0.02818 (15)	0.29173 (11)	0.0177 (2)
N11	0.48079 (13)	0.14996 (17)	0.08559 (13)	0.0131 (3)
C12	0.55480 (16)	−0.01067 (19)	0.15618 (17)	0.0121 (3)
C13	0.58539 (17)	−0.1785 (2)	0.07207 (15)	0.0146 (3)
H1A	0.6552	0.1734	0.5746	0.022*
H1B	0.5829	0.1501	0.4261	0.022*
H2A	0.7376	0.7191	0.5643	0.019*
H2B	0.6587	0.7357	0.4191	0.019*
H11	0.4704	0.2492	0.1388	0.016*
H13A	0.6980	−0.1949	0.1065	0.018*
H13B	0.5441	−0.3045	0.0943	0.018*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Co1	0.00921 (16)	0.00771 (16)	0.00769 (17)	0.00058 (8)	0.00276 (12)	−0.00047 (9)
Cl1	0.01405 (19)	0.01107 (19)	0.00752 (19)	0.00048 (11)	0.00200 (15)	−0.00086 (11)
O1	0.0198 (5)	0.0122 (5)	0.0094 (5)	0.0056 (4)	0.0029 (4)	−0.0012 (4)
O2	0.0147 (5)	0.0121 (5)	0.0108 (5)	−0.0013 (4)	0.0038 (4)	−0.0003 (4)
O12	0.0269 (6)	0.0146 (5)	0.0116 (5)	0.0027 (4)	0.0079 (5)	−0.0001 (4)
N11	0.0181 (6)	0.0112 (6)	0.0117 (6)	0.0025 (4)	0.0077 (5)	−0.0027 (4)
C12	0.0133 (7)	0.0117 (7)	0.0134 (7)	−0.0021 (5)	0.0074 (6)	−0.0017 (5)
C13	0.0218 (7)	0.0126 (7)	0.0113 (7)	0.0043 (5)	0.0086 (6)	0.0006 (5)

Geometric parameters (Å, º)

Co1—O1	2.0361 (9)	N11—C13^ii	1.4534 (18)
Co1—O1^i	2.0361 (9)	N11—H11	0.88
Co1—O2	2.1113 (9)	O2—H2A	0.84
Co1—O2^i	2.1113 (9)	O2—H2B	0.84
Co1—Cl1	2.4562 (3)	C12—O12	1.2476 (19)
Co1—Cl1^i	2.4562 (3)	C12—C13	1.4984 (19)
O1—H1A	0.84	C13—N11^ii	1.4534 (18)
O1—H1B	0.84	C13—H13A	0.99
N11—C12	1.3167 (18)	C13—H13B	0.99
O1—Co1—O2	91.86 (4)	C12—N11—C13^ii	126.05 (12)
O1^i—Co1—O2	88.14 (4)	C12—N11—H11	117.0
O1—Co1—O2^i	88.14 (4)	C13^ii—N11—H11	117.0
O1^i—Co1—O2^i	91.86 (4)	Co1—O2—H2A	111.8
O1—Co1—Cl1	92.55 (3)	Co1—O2—H2B	110.7
O1^i—Co1—Cl1	87.45 (3)	H2A—O2—H2B	105.9
O2—Co1—Cl1	89.37 (3)	O12—C12—N11	122.62 (13)
O2^i—Co1—Cl1	90.63 (3)	O12—C12—C13	118.10 (12)
O1—Co1—Cl1^i	87.45 (3)	N11—C12—C13	119.27 (13)
O1^i—Co1—Cl1^i	92.55 (3)	N11^ii—C13—C12	114.56 (12)
O2—Co1—Cl1^i	90.63 (3)	N11^ii—C13—H13A	108.6
O2^i—Co1—Cl1^i	89.37 (3)	C12—C13—H13A	108.6
Co1—O1—H1A	120.2	N11^ii—C13—H13B	108.6
Co1—O1—H1B	130.7	C12—C13—H13B	108.6
H1A—O1—H1B	109.0	H13A—C13—H13B	107.6
C13^ii—N11—C12—O12	−177.06 (13)	O12—C12—C13—N11^ii	177.47 (12)
C13^ii—N11—C12—C13	4.2 (2)	N11—C12—C13—N11^ii	−3.7 (2)

Symmetry codes: (i) −x+1, −y+1, −z+1; (ii) −x+1, −y, −z.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O1—H1A···Cl1^iii	0.84	2.35	3.1426 (10)	158
O1—H1B···O12	0.84	1.86	2.6901 (14)	167
O2—H2A···Cl1^iv	0.84	2.42	3.2302 (10)	163
O2—H2B···O12^v	0.84	1.96	2.7834 (14)	168
N11—H11···Cl1	0.88	2.38	3.2326 (12)	164

Symmetry codes: (iii) x+1/2, −y+1/2, z+1/2; (iv) x+1/2, −y+3/2, z+1/2; (v) x, y+1, z.

(II) trans-Tetraaquadichloridonickel(II)–piperazine-2,5-dione (1/1)

Crystal data

[NiCl2(H2O)4]·C4H6N2O2	F(000) = 324
Mr = 315.78	Dx = 1.826 Mg m^−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2yn	Cell parameters from 1315 reflections
a = 9.4844 (4) Å	θ = 3.8–27.5°
b = 6.6616 (3) Å	µ = 2.17 mm^−1
c = 9.9975 (4) Å	T = 120 K
β = 114.6290 (18)°	Block, colourless
V = 574.19 (4) Å^3	0.40 × 0.30 × 0.20 mm
Z = 2

Data collection

Nonius KappaCCD diffractometer	1315 independent reflections
Radiation source: Bruker Nonius FR591 rotating anode	1218 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.022
Detector resolution: 9.091 pixels mm^-1	θmax = 27.5°, θmin = 3.8°
ϕ and ω scans	h = −12→12
Absorption correction: multi-scan (SADABS; Sheldrick, 2003)	k = −8→8
Tmin = 0.468, Tmax = 0.649	l = −12→12
6275 measured reflections

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.019	H-atom parameters constrained
wR(F^2) = 0.046	w = 1/[σ^2(Fo^2) + (0.0167P)^2 + 0.3677P] where P = (Fo^2 + 2Fc^2)/3
S = 1.06	(Δ/σ)max < 0.001
1315 reflections	Δρmax = 0.35 e Å^−3
71 parameters	Δρmin = −0.34 e Å^−3
0 restraints	Extinction correction: SHELXL97 (Sheldrick, 2008), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.032 (2)

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
Ni1	0.5000	0.5000	0.5000	0.00809 (10)
Cl1	0.37016 (4)	0.51186 (4)	0.23679 (3)	0.01131 (10)
O1	0.59374 (11)	0.22730 (14)	0.49672 (10)	0.0160 (2)
O2	0.68915 (10)	0.64843 (14)	0.49002 (10)	0.0128 (2)
O12	0.60300 (12)	−0.03041 (15)	0.29286 (11)	0.0182 (2)
N11	0.48200 (13)	0.15055 (16)	0.08636 (12)	0.0128 (2)
C12	0.55513 (15)	−0.01192 (18)	0.15700 (15)	0.0119 (3)
C13	0.58485 (16)	−0.1796 (2)	0.07224 (14)	0.0146 (3)
H1A	0.6519	0.1739	0.5770	0.024*
H1B	0.5819	0.1525	0.4252	0.024*
H2A	0.7343	0.7168	0.5667	0.019*
H2B	0.6541	0.7327	0.4215	0.019*
H11	0.4729	0.2502	0.1400	0.015*
H13A	0.6983	−0.1969	0.1075	0.018*
H13B	0.5427	−0.3053	0.0939	0.018*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Ni1	0.00879 (14)	0.00747 (14)	0.00677 (14)	0.00066 (7)	0.00200 (9)	−0.00034 (7)
Cl1	0.01365 (17)	0.01068 (17)	0.00688 (16)	0.00055 (10)	0.00159 (12)	−0.00093 (10)
O1	0.0225 (5)	0.0126 (5)	0.0084 (4)	0.0076 (4)	0.0019 (4)	−0.0010 (4)
O2	0.0136 (4)	0.0122 (4)	0.0107 (4)	−0.0011 (3)	0.0030 (3)	0.0009 (4)
O12	0.0282 (6)	0.0153 (5)	0.0102 (5)	0.0032 (4)	0.0073 (4)	−0.0003 (4)
N11	0.0186 (6)	0.0104 (5)	0.0106 (5)	0.0024 (4)	0.0073 (4)	−0.0027 (4)
C12	0.0135 (6)	0.0117 (6)	0.0120 (6)	−0.0020 (4)	0.0065 (5)	−0.0015 (5)
C13	0.0221 (7)	0.0120 (6)	0.0116 (6)	0.0055 (5)	0.0090 (5)	0.0017 (5)

Geometric parameters (Å, º)

Ni1—O1	2.0287 (9)	O2—H2B	0.8399
Ni1—O1^i	2.0287 (9)	N11—C12	1.3202 (17)
Ni1—O2	2.0869 (9)	N11—C13^ii	1.4545 (16)
Ni1—O2^i	2.0869 (9)	N11—H11	0.88
Ni1—Cl1	2.3971 (3)	C12—O12	1.2459 (17)
Ni1—Cl1^i	2.3971 (3)	C12—C13	1.4980 (18)
O1—H1A	0.8398	C13—N11^ii	1.4545 (16)
O1—H1B	0.8399	C13—H13A	0.99
O2—H2A	0.8399	C13—H13B	0.99
O1—Ni1—O2	91.85 (4)	Ni1—O2—H2A	109.6
O1^i—Ni1—O2	88.15 (4)	Ni1—O2—H2B	107.5
O1—Ni1—O2^i	88.15 (4)	H2A—O2—H2B	105.1
O1^i—Ni1—O2^i	91.85 (4)	C12—N11—C13^ii	125.82 (11)
O1—Ni1—Cl1	92.29 (3)	C12—N11—H11	117.1
O1^i—Ni1—Cl1	87.71 (3)	C13^ii—N11—H11	117.1
O2—Ni1—Cl1	89.45 (3)	O12—C12—N11	122.39 (12)
O2^i—Ni1—Cl1	90.55 (3)	O12—C12—C13	118.30 (11)
O1—Ni1—Cl1^i	87.71 (3)	N11—C12—C13	119.30 (12)
O1^i—Ni1—Cl1^i	92.29 (3)	N11^ii—C13—C12	114.72 (11)
O2—Ni1—Cl1^i	90.55 (3)	N11^ii—C13—H13A	108.6
O2^i—Ni1—Cl1^i	89.45 (3)	C12—C13—H13A	108.6
Ni1—O1—H1A	118.8	N11^ii—C13—H13B	108.6
Ni1—O1—H1B	129.9	C12—C13—H13B	108.6
H1A—O1—H1B	111.3	H13A—C13—H13B	107.6
C13^ii—N11—C12—O12	−176.40 (13)	O12—C12—C13—N11^ii	176.86 (12)
C13^ii—N11—C12—C13	4.7 (2)	N11—C12—C13—N11^ii	−4.23 (19)

Symmetry codes: (i) −x+1, −y+1, −z+1; (ii) −x+1, −y, −z.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O1—H1A···Cl1^iii	0.84	2.37	3.1508 (10)	155
O1—H1B···O12	0.84	1.87	2.6941 (13)	167
O2—H2A···Cl1^iv	0.84	2.45	3.2596 (9)	163
O2—H2B···O12^v	0.84	1.96	2.7906 (13)	168
N11—H11···Cl1	0.88	2.39	3.2419 (11)	163

Symmetry codes: (iii) x+1/2, −y+1/2, z+1/2; (iv) x+1/2, −y+3/2, z+1/2; (v) x, y+1, z.

(III) catena-poly[[[trans-diaquacopper(II)]-di-µ-chlorido] piperazine-2,5-dione solvate]

Crystal data

[CuCl2(H2O)2]·C4H6N2O2	F(000) = 572
Mr = 284.58	Dx = 2.032 Mg m^−3
Monoclinic, I2/a	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -I 2ya	Cell parameters from 1059 reflections
a = 15.224 (3) Å	θ = 3.6–27.5°
b = 3.9694 (8) Å	µ = 2.91 mm^−1
c = 15.444 (4) Å	T = 120 K
β = 94.73 (3)°	Needle, blue-green
V = 930.1 (4) Å^3	0.16 × 0.04 × 0.03 mm
Z = 4

Data collection

Nonius KappaCCD diffractometer	1059 independent reflections
Radiation source: Bruker Nonius FR591 rotating anode	787 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.0
Detector resolution: 9.091 pixels mm^-1	θmax = 27.5°, θmin = 3.6°
ϕ and ω scans	h = −19→19
Absorption correction: multi-scan (SADABS; Sheldrick, 2003)	k = −5→5
Tmin = 0.654, Tmax = 0.918	l = −12→19
4485 measured reflections

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.058	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.164	H-atom parameters constrained
S = 1.09	w = 1/[σ^2(Fo^2) + (0.0721P)^2 + 6.6393P] where P = (Fo^2 + 2Fc^2)/3
1059 reflections	(Δ/σ)max < 0.001
62 parameters	Δρmax = 1.58 e Å^−3
0 restraints	Δρmin = −1.45 e Å^−3

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
Cu1	0.2500	0.2500	0.2500	0.0182 (4)
Cl1	0.24586 (10)	0.5930 (4)	0.36560 (10)	0.0215 (4)
O1	0.3780 (3)	0.2422 (12)	0.2634 (3)	0.0205 (10)
O12	0.5031 (3)	0.6199 (13)	0.3563 (3)	0.0212 (10)
N11	0.4258 (3)	0.8700 (15)	0.4572 (3)	0.0195 (12)
C12	0.5002 (4)	0.7978 (16)	0.4227 (4)	0.0158 (13)
C13	0.4159 (4)	1.0630 (18)	0.5352 (4)	0.0186 (14)
H1A	0.4111	0.4021	0.2915	0.031*
H1B	0.4101	0.1948	0.2185	0.031*
H11	0.3805	0.7841	0.4255	0.023*
H13A	0.3886	0.9173	0.5776	0.022*
H13B	0.3749	1.2521	0.5207	0.022*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cu1	0.0160 (5)	0.0241 (7)	0.0146 (6)	0.0010 (5)	0.0008 (4)	−0.0071 (5)
Cl1	0.0181 (7)	0.0294 (9)	0.0171 (7)	−0.0019 (7)	0.0018 (5)	−0.0116 (7)
O1	0.0127 (19)	0.029 (3)	0.020 (2)	−0.002 (2)	0.0015 (17)	−0.008 (2)
O12	0.021 (2)	0.031 (3)	0.011 (2)	−0.004 (2)	0.0012 (17)	−0.005 (2)
N11	0.017 (2)	0.026 (3)	0.015 (3)	−0.006 (2)	−0.003 (2)	−0.004 (2)
C12	0.015 (3)	0.020 (4)	0.012 (3)	−0.002 (2)	0.001 (2)	0.004 (3)
C13	0.015 (3)	0.023 (4)	0.017 (3)	0.001 (3)	0.000 (2)	0.000 (3)

Geometric parameters (Å, º)

Cu1—O1^i	1.942 (4)	N11—C13	1.446 (8)
Cu1—O1	1.942 (4)	N11—H11	0.88
Cu1—Cl1	2.2502 (15)	C12—O12	1.249 (8)
Cu1—Cl1^i	2.2502 (15)	C12—C13^iii	1.492 (8)
Cu1—Cl1^ii	3.1640 (18)	C13—C12^iii	1.492 (8)
O1—H1A	0.90	C13—H13A	0.99
O1—H1B	0.90	C13—H13B	0.99
N11—C12	1.322 (8)
O1^i—Cu1—Cl1	88.92 (14)	O12—C12—N11	122.9 (6)
O1—Cu1—Cl1	91.08 (14)	O12—C12—C13^iii	118.6 (5)
O1^i—Cu1—Cl1^i	91.08 (14)	N11—C12—C13^iii	118.4 (6)
O1—Cu1—Cl1^i	88.92 (14)	N11—C13—C12^iii	114.5 (5)
Cu1—O1—H1A	123.9	N11—C13—H13A	108.6
Cu1—O1—H1B	121.7	C12^iii—C13—H13A	108.6
H1A—O1—H1B	101.6	N11—C13—H13B	108.6
C12—N11—C13	127.0 (5)	C12^iii—C13—H13B	108.6
C12—N11—H11	110.5	H13A—C13—H13B	107.6
C13—N11—H11	122.5
C13—N11—C12—O12	177.7 (6)	C12—N11—C13—C12^iii	2.6 (11)
C13—N11—C12—C13^iii	−2.7 (11)

Symmetry codes: (i) −x+1/2, −y+1/2, −z+1/2; (ii) x, y−1, z; (iii) −x+1, −y+2, −z+1.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O1—H1A···O12	0.90	1.87	2.737 (6)	162
O1—H1B···O12^iv	0.90	1.85	2.735 (6)	167
N11—H11···Cl1	0.88	2.31	3.174 (5)	168

Symmetry code: (iv) −x+1, y−1/2, −z+1/2.

(IV) silver(I) nitrate–piperazine-2.5-dione (1/1)

Crystal data

[Ag(NO3)]·C4H6N2O2	F(000) = 552
Mr = 567.98	Dx = 2.537 Mg m^−3
Orthorhombic, Pnma	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ac 2n	Cell parameters from 888 reflections
a = 9.6276 (1) Å	θ = 4.1–27.6°
b = 14.7180 (2) Å	µ = 2.71 mm^−1
c = 5.2468 (4) Å	T = 120 K
V = 743.47 (6) Å^3	Plate, colourless
Z = 2	0.42 × 0.22 × 0.12 mm

Data collection

Nonius KappaCCD diffractometer	888 independent reflections
Radiation source: fine-focus sealed X-ray tube	826 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.041
Detector resolution: 9.091 pixels mm^-1	θmax = 27.6°, θmin = 4.1°
ϕ and ω scans	h = −12→11
Absorption correction: multi-scan SORTAV (Blessing, 1995, 1997)	k = −19→19
Tmin = 0.389, Tmax = 0.722	l = −6→6
7016 measured reflections

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.017	H-atom parameters constrained
wR(F^2) = 0.044	w = 1/[σ^2(Fo^2) + (0.0202P)^2 + 0.4734P] where P = (Fo^2 + 2Fc^2)/3
S = 1.09	(Δ/σ)max = 0.001
888 reflections	Δρmax = 0.44 e Å^−3
68 parameters	Δρmin = −0.44 e Å^−3
0 restraints	Extinction correction: SHELXL97 (Sheldrick, 2008), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.0155 (9)

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
Ag1	0.587751 (19)	0.2500	0.49038 (3)	0.01324 (11)
O1	0.6353 (2)	0.2500	0.9570 (4)	0.0239 (4)
O2	0.81536 (18)	0.2500	1.2012 (3)	0.0161 (4)
O3	0.83942 (18)	0.2500	0.7908 (4)	0.0204 (4)
O12	0.59454 (12)	0.40743 (9)	0.4032 (3)	0.0185 (3)
N1	0.7620 (2)	0.2500	0.9817 (3)	0.0107 (4)
N11	0.44162 (15)	0.41922 (10)	0.0797 (3)	0.0170 (3)
C12	0.54788 (17)	0.44853 (11)	0.2160 (3)	0.0139 (3)
C13	0.61478 (17)	0.53704 (12)	0.1454 (3)	0.0153 (4)
H11	0.4014	0.3686	0.1300	0.020*
H13A	0.6056	0.5793	0.2912	0.018*
H13B	0.7152	0.5263	0.1178	0.018*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Ag1	0.01476 (15)	0.01149 (15)	0.01348 (16)	0.000	−0.00071 (6)	0.000
O1	0.0126 (10)	0.0395 (13)	0.0197 (9)	0.000	−0.0030 (7)	0.000
O2	0.0203 (8)	0.0132 (8)	0.0149 (8)	0.000	−0.0076 (7)	0.000
O3	0.0219 (9)	0.0201 (10)	0.0193 (9)	0.000	0.0065 (8)	0.000
O12	0.0216 (6)	0.0148 (7)	0.0190 (7)	−0.0014 (5)	−0.0047 (5)	0.0039 (5)
N1	0.0136 (10)	0.0066 (9)	0.0119 (10)	0.000	−0.0018 (7)	0.000
N11	0.0179 (7)	0.0124 (7)	0.0207 (8)	−0.0042 (6)	−0.0028 (7)	0.0058 (6)
C12	0.0134 (7)	0.0123 (8)	0.0159 (8)	0.0008 (6)	0.0022 (6)	−0.0008 (6)
C13	0.0158 (7)	0.0150 (9)	0.0153 (8)	−0.0034 (6)	−0.0011 (7)	0.0026 (6)

Geometric parameters (Å, º)

Ag1—O1	2.4907 (18)	N11—C12	1.321 (2)
Ag1—O2^i	2.6653 (17)	N11—C13^iii	1.451 (2)
Ag1—O3^ii	2.6522 (18)	N11—H11	0.88
Ag1—O12	2.3627 (13)	C12—O12	1.238 (2)
N1—O1	1.226 (3)	C12—C13	1.500 (2)
N1—O3	1.249 (3)	C13—H13A	0.99
N1—O2	1.261 (3)	C13—H13B	0.99
O1—Ag1—O2^i	114.11 (6)	C12—N11—H11	117.1
O1—Ag1—O3^ii	74.94 (6)	C13^iii—N11—H11	117.1
O1—Ag1—O12	100.67 (3)	O12—C12—N11	123.44 (15)
O12—Ag1—O12^iv	157.45 (7)	O12—C12—C13	117.67 (15)
O2^i—Ag1—O3^ii	170.95 (6)	N11—C12—C13	118.87 (15)
O2^i—Ag1—O12	82.36 (3)	C12—O12—Ag1	128.51 (11)
O3^ii—Ag1—O12	96.24 (3)	N11^iii—C13—C12	115.20 (14)
O1—N1—O3	120.58 (19)	N11^iii—C13—H13A	108.5
O1—N1—O2	120.1 (2)	C12—C13—H13A	108.5
O3—N1—O2	119.3 (2)	N11^iii—C13—H13B	108.5
N1—O1—Ag1	106.68 (14)	C12—C13—H13B	108.5
C12—N11—C13^iii	125.86 (14)	H13A—C13—H13B	107.5
O12^iv—Ag1—O1—N1	86.34 (3)	C13—C12—O12—Ag1	−153.91 (11)
O12—Ag1—O1—N1	−86.34 (3)	O12^iv—Ag1—O12—C12	37.0 (2)
C13^iii—N11—C12—O12	−178.05 (17)	O1—Ag1—O12—C12	−162.03 (14)
C13^iii—N11—C12—C13	3.2 (3)	O12—C12—C13—N11^iii	178.31 (16)
N11—C12—O12—Ag1	27.3 (2)	N11—C12—C13—N11^iii	−2.8 (3)

Symmetry codes: (i) x, y, z−1; (ii) x−1/2, −y+1/2, −z+3/2; (iii) −x+1, −y+1, −z; (iv) x, −y+1/2, z.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N11—H11···O2^v	0.88	2.13	3.0004 (18)	173

Symmetry code: (v) x−1/2, y, −z+3/2.