Crystal structure of catena-poly[[cadmium(II)-di-μ2-bromido-μ2-l-proline-κ(2) O:O'] monohydrate].

In the title coordination polymer, {[CdBr2(C5H9NO2)]·H2O} n , the Cd(II) ion is coordinated by four bromido ligands and two carboxyl-ate oxygen atoms of two symmetry-related proline ligands, which exist in a zwitterionic form, in a distorted octa-hedral geometry. There is an intra-molecular N-H⋯O hydrogen bond between the amino group and the carboxyl-ate fragment. Each coordinating ligand bridges two Cd(II) atoms, thus forming polymeric chains running along the c-axis direction. The water mol-ecules of crystallization serve as donors for the weak inter-molecular O-H⋯O and O-H⋯Br hydrogen bonds that link adjacent polymeric chains, thus forming a three-dimensional structure. N-H⋯O and N-H⋯Br hydrogen bonds also occur.

Chemical context

The characterization of second-order non-linear optical (NLO) materials is important because of their potential applications such as frequency shifting, optical modulation, optical switching, telecommunication and signal processing. It is known that the chiral amino acids and their complexes are potential materials for n class="Chemical">NLO applications (Eimerl et al., 1989 ▸; Pal et al., 2004 ▸; Srinivasan et al., 2006 ▸). This study is a part of an ongoing investigation of the crystal and mol­ecular structures of a series of amino acid–metal complexes (Sathiskumar et al., 2015 ▸; Balakrishnan et al., 2013 ▸).

Structural commentary

The asymmetric unit of the title complex (I) (Fig. 1 ▸) contains one CdII ion, one proline and two bromido ligands, and one n class="Chemical">water mol­ecule of crystallization. The title complex has a very similar structure to that of the chloride analogue (Yukawa et al., 1983 ▸) and l-proline manganese dichloride monohydrate (Rzączyńska et al., 1997 ▸; Lamberts & Englert, 2012 ▸). In (I), proline exists in a zwitterionic form, as evident from the bond lengths involving the carboxyl­ate atoms and the protonation of the ring N atom of the pyrrolidine fragment. The CdII ion is coordinated by four bromido ligands [Cd—Br = 2.7236 (13)–2.7737 (12) Å] and two carboxyl­ate oxygen atoms [Cd—O = 2.312 (8) and 2.318 (8) Å] of two proline ligands in a slightly distorted octa­hedral geometry. The title complex is extended as a polymeric chain which runs parallel to the c axis. Within one chain, adjacent CdII ions are separated by 3.727 (1) Å. The closest Cd⋯Cd distance between neighbouring polymeric chains is 8.579 (2) Å. The five endocyclic torsion angles of the pyrrolidine ring of the proline residue are N1—C2—C3—C4 = 31.8 (13)°, C2—C3—C4—C5 = −39.1 (15)°, C3—C4—C5—N1 = 29.9 (14)°, C2—N1—C5—C4 = −9.7 (12)° and C5—N1—C2—C3 = −13.1 (11)°. The pyrrolidine ring exhibits twisted conformation on the C3—C4 bond with a pseudo-rotation angle Δ = 249.3 (12)° and a maximum torsion angle ϕm = 38.5 (8)° (Rao et al., 1981 ▸).

Figure 1

A portion of the crystal structure of the title complex, showing the atomic labeling. Displacement ellipsoids are drawn at the 30% probability level. [Symmetry codes: (a)  − x, −y, z − ; (b)  − x, −y, z + .]

In (I), as observed in the chloride analogue (Yukawa et al., 1983 ▸), there is an intra­molecular N1—H1A⋯O2 hydrogen bond between the amino group and the carboxyl­ate fragment.

Supra­molecular features

The crystal structure of (I), is stabilized by inter­molecular N—H⋯O, n class="Chemical">N—H⋯Br, O—H⋯O and O—H⋯Br hydrogen bonds (Table 1 ▸, Figs. 2 ▸ and 3 ▸). The water mol­ecules serve as donors for the weak O—H⋯O and O—H⋯Br hydrogen bonds (Table 1 ▸) which link adjacent polymeric chains (Fig. 3 ▸), thus forming a three-dimensional structure.

Table 1

Hydrogen-bond geometry (, )

DHA	DH	HA	D A	DHA
N1H1AO2	0.89	2.16	2.626(12)	112
O1WH2WO1	0.84(17)	2.6(2)	3.175(19)	132
O1WH2WBr2	0.84(17)	2.8(3)	3.311(19)	123
N1H1AO1W i	0.89	2.05	2.90(2)	159
N1H1BBr1ii	0.89	2.69	3.416(11)	140
O1WH1WBr2iii	0.88(16)	2.7(3)	3.197(19)	116

Symmetry codes: (i) ; (ii) ; (iii) .

Figure 2

The crystal packing of (I) viewed along the a axis. Dashed lines denote inter­molecular hydrogen bonds. C-bound H atoms have been omitted for clarity.

Figure 3

A portion of the crystal packing viewed along the a axis and showing hydrogen bonds (dashed lines) between two neighbouring polymeric chains.

Database survey

A search in the Cambridge Structural Database (Version 5.35, last update May 2014; Groom & Allen, 2014 ▸) for the structures with metal ions coordinated by one of the carboxyl­ate n class="Chemical">oxygen atoms of the proline moiety yielded 44 hits. Of these, two structures contain a cadmium metal ion, viz. catena-[di­chlorido-(4-hy­droxy-l-proline)cadmium] (refcode BOHVID; Yukawa et al., 1982 ▸) and catena-[bis­(μ2-chlorido)(μ2-l-pro­line)cadmium monohydrate] (refcode BUXBUR; Yukawa et al., 1983 ▸). The latter structure is isotypic with the title complex. Another compound, catena-[bis­(μ2-chlorido)(μ2-l-prolinato-κ2-O,O′)manganese(II) monohydrate], has been structurally determined three times and has similar cell parameters and the same space group as the title compound (refcode ROJQEM: Rzączyńska et al., 1997 ▸; refcode ROJEQM01: Tilborg et al., 2010 ▸; refcode ROJQEM02: Lamberts & Englert, 2012 ▸).

Synthesis and crystallization

To prepare the title compound, l-proline (Loba) and cadmium bromide tetra­hydrate (Loba) in an equimolar ratio were dissolved in double-distilled water. The obtained solution of the homogeneous mixture was evaporated at room temperature to afford the white crystalline title compound, which was then recrystallized by slow evaporation from an aqueous solution.

Refinement

Crystal data, data collection and structure refinement details are summarized in Table 2 ▸. As the title compound is isotypic with its chlorido analogue (Yukawa et al., 1983 ▸), the atomic coordinates of the latter were used as starting values in the initial cycles of the refinement. The positions of water n class="Chemical">hydrogen atoms were calculated by method of Nardelli (1999 ▸). Further, the O—H and H1W⋯H2W distances of the water mol­ecules were restrained to 0.85 (2) and 1.38 (2) Å, respectively, using the DFIX option and included in the structure-factor calculations with U iso(H1W/H2W) = 1.1U eq(O1W). The remaining hydrogen atoms were placed in geometrically idealized positions (C—H = 0.97–0.98 Å and N—H = 0.89 Å) with U iso(H) = 1.2U eq(C/N) and were constrained to ride on their parent atoms. Reflections 110 and 020 were partially obscured by the beam stop and were omitted.

Table 2

Experimental details

Crystal data
Chemical formula	[CdBr2(C5H9NO2)]H2O
M r	405.37
Crystal system, space group	Orthorhombic, P212121
Temperature (K)	296
a, b, c ()	10.1891(8), 13.4961(11), 7.4491(5)
V (3)	1024.35(13)
Z	4
Radiation type	Mo K
(mm1)	9.90
Crystal size (mm)	0.35 0.30 0.30
Data collection
Diffractometer	Bruker SMART CCD area detector
Absorption correction	Multi-scan (SADABS; Bruker, 2008 ▸)
T min, T max	0.129, 0.155
No. of measured, independent and observed [I > 2(I)] reflections	8264, 2481, 1964
R int	0.068
(sin /)max (1)	0.666
Refinement
R[F 2 > 2(F 2)], wR(F 2), S	0.041, 0.089, 1.06
No. of reflections	2481
No. of parameters	115
No. of restraints	3
H-atom treatment	H atoms treated by a mixture of independent and constrained refinement
max, min (e 3)	1.02, 1.07
Absolute structure	Flack x determined using 705 quotients [(I +)(I )]/[(I +)+(I )] (Parsons et al., 2013 ▸)
Absolute structure parameter	0.035(15)

Computer programs: APEX2, SAINT and XPREP (Bruker, 2008 ▸), SHELXL2014/6 (Sheldrick, 2015 ▸), PLATON (Spek, 2009 ▸) and Mercury (Macrae et al., 2008 ▸).

Crystal structure: contains datablock(s) I. DOI: 10.1107/S2056989015001176/cv5483sup1.cif

Structure factors: contains datablock(s) I. DOI: 10.1107/S2056989015001176/cv5483Isup2.hkl

CCDC reference: 1044327

Additional supporting information: crystallographic information; 3D view; checkCIF report

[CdBr2(C5H9NO2)]·H2O	Dx = 2.629 Mg m−3
Mr = 405.37	Mo Kα radiation, λ = 0.71073 Å
Orthorhombic, P212121	Cell parameters from 4066 reflections
a = 10.1891 (8) Å	θ = 5.0–55.2°
b = 13.4961 (11) Å	µ = 9.90 mm−1
c = 7.4491 (5) Å	T = 296 K
V = 1024.35 (13) Å3	Block, colourless
Z = 4	0.35 × 0.30 × 0.30 mm
F(000) = 760

Bruker SMART CCD area detector diffractometer	1964 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.068
ω and φ scan	θmax = 28.2°, θmin = 3.1°
Absorption correction: multi-scan (SADABS; Bruker, 2008)	h = −13→13
Tmin = 0.129, Tmax = 0.155	k = −17→14
8264 measured reflections	l = −9→6
2481 independent reflections

Refinement on F2	Hydrogen site location: mixed
Least-squares matrix: full	H atoms treated by a mixture of independent and constrained refinement
R[F2 > 2σ(F2)] = 0.041	w = 1/[σ2(Fo2) + (0.0243P)2 + 1.4185P] where P = (Fo2 + 2Fc2)/3
wR(F2) = 0.089	(Δ/σ)max < 0.001
S = 1.06	Δρmax = 1.02 e Å−3
2481 reflections	Δρmin = −1.07 e Å−3
115 parameters	Absolute structure: Flack x determined using 705 quotients [(I+)-(I-)]/[(I+)+(I-)] (Parsons et al., 2013)
3 restraints	Absolute structure parameter: 0.035 (15)

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

	x	y	z	Uiso*/Ueq
Cd1	0.24415 (7)	0.00192 (7)	0.31349 (9)	0.0425 (2)
Br1	0.44442 (8)	0.03071 (8)	0.06673 (14)	0.0450 (3)
Br2	0.37743 (10)	0.11262 (9)	0.56256 (15)	0.0537 (3)
O1	0.1309 (8)	0.1397 (6)	0.2136 (9)	0.057 (2)
O2	0.1420 (7)	0.1362 (6)	−0.0865 (9)	0.056 (2)
N1	−0.0870 (10)	0.2205 (8)	−0.1393 (11)	0.062 (3)
H1A	−0.0168	0.2171	−0.2100	0.075*
H1B	−0.1202	0.2813	−0.1471	0.075*
C1	0.0861 (9)	0.1560 (7)	0.0564 (15)	0.039 (2)
C2	−0.0488 (10)	0.1988 (8)	0.0510 (15)	0.053 (3)
H2	−0.0524	0.2596	0.1229	0.064*
C3	−0.1523 (12)	0.1260 (13)	0.115 (2)	0.084 (5)
H3A	−0.1172	0.0826	0.2066	0.100*
H3B	−0.2279	0.1607	0.1627	0.100*
C4	−0.1878 (13)	0.0697 (13)	−0.047 (2)	0.094 (5)
H4A	−0.2733	0.0392	−0.0326	0.113*
H4B	−0.1236	0.0181	−0.0701	0.113*
C5	−0.1899 (14)	0.1441 (12)	−0.200 (2)	0.086 (5)
H5A	−0.2758	0.1743	−0.2126	0.103*
H5B	−0.1651	0.1134	−0.3127	0.103*
O1W	0.111 (2)	0.2521 (17)	0.587 (2)	0.183 (8)
H1W	0.11 (3)	0.296 (11)	0.50 (2)	0.201*
H2W	0.13 (3)	0.197 (8)	0.54 (3)	0.201*

	U11	U22	U33	U12	U13	U23
Cd1	0.0453 (4)	0.0579 (4)	0.0243 (3)	0.0069 (4)	−0.0005 (2)	0.0045 (3)
Br1	0.0347 (4)	0.0679 (7)	0.0323 (4)	0.0033 (5)	−0.0007 (4)	−0.0001 (5)
Br2	0.0597 (6)	0.0687 (7)	0.0327 (5)	−0.0117 (6)	0.0013 (5)	−0.0056 (6)
O1	0.074 (5)	0.066 (5)	0.032 (4)	0.025 (4)	−0.011 (3)	−0.005 (4)
O2	0.059 (5)	0.068 (5)	0.043 (4)	0.016 (4)	0.005 (4)	0.007 (4)
N1	0.063 (6)	0.066 (7)	0.058 (6)	0.037 (6)	−0.015 (5)	−0.001 (5)
C1	0.040 (5)	0.039 (5)	0.039 (5)	0.005 (4)	−0.002 (5)	−0.003 (5)
C2	0.053 (6)	0.060 (7)	0.046 (5)	0.024 (6)	−0.009 (6)	−0.010 (6)
C3	0.043 (7)	0.113 (13)	0.095 (10)	0.005 (8)	0.018 (6)	0.008 (10)
C4	0.042 (6)	0.110 (12)	0.130 (13)	−0.008 (8)	0.006 (9)	−0.021 (13)
C5	0.075 (9)	0.090 (11)	0.091 (10)	0.040 (9)	−0.024 (8)	−0.037 (9)
O1W	0.178 (16)	0.22 (2)	0.153 (13)	0.061 (18)	0.007 (14)	0.061 (17)

Cd1—O1	2.312 (8)	N1—H1B	0.8900
Cd1—O2i	2.318 (8)	C1—C2	1.491 (13)
Cd1—Br2ii	2.7236 (13)	C2—C3	1.517 (19)
Cd1—Br1i	2.7285 (11)	C2—H2	0.9800
Cd1—Br2	2.7421 (13)	C3—C4	1.47 (2)
Cd1—Br1	2.7737 (12)	C3—H3A	0.9700
Br1—Cd1ii	2.7285 (11)	C3—H3B	0.9700
Br2—Cd1i	2.7236 (13)	C4—C5	1.52 (2)
O1—C1	1.276 (12)	C4—H4A	0.9700
O2—C1	1.237 (12)	C4—H4B	0.9700
O2—Cd1ii	2.318 (8)	C5—H5A	0.9700
N1—C2	1.499 (13)	C5—H5B	0.9700
N1—C5	1.537 (17)	O1W—H1W	0.87 (3)
N1—H1A	0.8900	O1W—H2W	0.87 (3)
O1—Cd1—O2i	179.9 (3)	O1—C1—C2	114.9 (9)
O1—Cd1—Br2ii	90.50 (19)	C1—C2—N1	109.9 (9)
O2i—Cd1—Br2ii	89.53 (19)	C1—C2—C3	112.4 (10)
O1—Cd1—Br1i	90.0 (2)	N1—C2—C3	103.9 (10)
O2i—Cd1—Br1i	90.03 (19)	C1—C2—H2	110.1
Br2ii—Cd1—Br1i	93.59 (4)	N1—C2—H2	110.1
O1—Cd1—Br2	91.52 (19)	C3—C2—H2	110.1
O2i—Cd1—Br2	88.44 (19)	C4—C3—C2	104.5 (11)
Br2ii—Cd1—Br2	177.29 (3)	C4—C3—H3A	110.9
Br1i—Cd1—Br2	88.22 (3)	C2—C3—H3A	110.9
O1—Cd1—Br1	92.4 (2)	C4—C3—H3B	110.9
O2i—Cd1—Br1	87.56 (19)	C2—C3—H3B	110.9
Br2ii—Cd1—Br1	87.67 (4)	H3A—C3—H3B	108.9
Br1i—Cd1—Br1	177.27 (4)	C3—C4—C5	106.0 (12)
Br2—Cd1—Br1	90.44 (4)	C3—C4—H4A	110.5
Cd1ii—Br1—Cd1	85.27 (3)	C5—C4—H4A	110.5
Cd1i—Br2—Cd1	85.98 (3)	C3—C4—H4B	110.5
C1—O1—Cd1	127.7 (6)	C5—C4—H4B	110.5
C1—O2—Cd1ii	132.9 (7)	H4A—C4—H4B	108.7
C2—N1—C5	108.9 (10)	C4—C5—N1	102.3 (10)
C2—N1—H1A	109.9	C4—C5—H5A	111.3
C5—N1—H1A	109.9	N1—C5—H5A	111.3
C2—N1—H1B	109.9	C4—C5—H5B	111.3
C5—N1—H1B	109.9	N1—C5—H5B	111.3
H1A—N1—H1B	108.3	H5A—C5—H5B	109.2
O2—C1—O1	126.0 (8)	H1W—O1W—H2W	106 (4)
O2—C1—C2	119.0 (10)
Cd1ii—O2—C1—O1	44.5 (15)	C5—N1—C2—C1	107.4 (11)
Cd1ii—O2—C1—C2	−132.7 (9)	C5—N1—C2—C3	−13.1 (11)
Cd1—O1—C1—O2	−40.4 (15)	C1—C2—C3—C4	−87.0 (14)
Cd1—O1—C1—C2	136.8 (8)	N1—C2—C3—C4	31.8 (13)
O2—C1—C2—N1	−6.1 (15)	C2—C3—C4—C5	−39.1 (15)
O1—C1—C2—N1	176.4 (9)	C3—C4—C5—N1	29.9 (14)
O2—C1—C2—C3	109.1 (12)	C2—N1—C5—C4	−9.7 (12)
O1—C1—C2—C3	−68.3 (13)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1A···O2	0.89	2.16	2.626 (12)	112
O1W—H2W···O1	0.84 (17)	2.6 (2)	3.175 (19)	132
O1W—H2W···Br2	0.84 (17)	2.8 (3)	3.311 (19)	123
N1—H1A···O1Wiii	0.89	2.05	2.90 (2)	159
N1—H1B···Br1iv	0.89	2.69	3.416 (11)	140
O1W—H1W···Br2v	0.88 (16)	2.7 (3)	3.197 (19)	116