catena-Poly[[[tetra­aqua­copper(II)]-μ-4,4′-bipyridyl-κ2N:N′] tetra­fluorido­succinate tetra­hydrate]

Yu, G.-J.; Xu, L.-P.; Qin, L.; Han, L.

doi:10.1107/S1600536812014948

metal-organic compounds

CRYSTALLOGRAPHIC
COMMUNICATIONS

ISSN: 2056-9890

Volume 68| Part 5| May 2012| Page m598

doi:10.1107/S1600536812014948

Open

access

catena-Poly[[[tetraaquacopper(II)]-μ-4,4′-bipyridyl-κ²N:N′] tetrafluoridosuccinate tetrahydrate]

Guo-Jun Yu,^a Lan-Ping Xu,^a Lan Qin ^a and Lei Han ^a ^*

^aFaculty of Materials Science & Chemical Engineering, Ningbo University, Ningbo, Zhejiang 315211, People's Republic of China
^*Correspondence e-mail: hanlei@nbu.edu.cn

(Received 22 March 2012; accepted 5 April 2012; online 18 April 2012)

In the title compound, {[Cu(C₁₀H₈N₂)(H₂O)₄](C₄F₄O₄)·4H₂O}_n, the Cu^II atom adopts an elongated octahedral geometry because of the Jahn–Teller effect. Both cation and anion have crystallographic twofold rotation symmetry with the twofold axes passing through the Cu and N atoms and through the midpoint of the central C—C bond. The 4,4′-bipyridyl ligand links the Cu^II atoms into a linear chain along the b axis. O—H⋯O hydrogen-bonding interactions between the cationic chains and the tetrafluoridosuccinate anions and the free water molecules generate a three-dimensional supramolecular network.

Related literature

For background to metal-organic framework structures, see: Allendorf et al. (2009 ). For the construction of hybrid frameworks with perfluorinated ligands, see: Yang et al. (2007 ); Hulvey et al. (2009 ).

Experimental

Crystal data

[Cu(C₁₀H₈N₂)(H₂O)₄](C₄F₄O₄)·4H₂O
M_r = 551.89
Monoclinic, C 2/c
a = 17.112 (3) Å
b = 11.135 (2) Å
c = 12.126 (2) Å
β = 104.85 (3)°
V = 2233.3 (7) Å³
Z = 4
Mo Kα radiation
μ = 1.07 mm⁻¹
T = 298 K
0.44 × 0.22 × 0.10 mm

Data collection

Bruker SMART APEX diffractometer
Absorption correction: multi-scan (SADABS; Bruker, 2005 ) T_min = 0.650, T_max = 0.900
10662 measured reflections
2546 independent reflections
2115 reflections with I > 2σ(I)
R_int = 0.026

Refinement

R[F² > 2σ(F²)] = 0.027
wR(F²) = 0.085
S = 1.28
2546 reflections
153 parameters
H-atom parameters constrained
Δρ_max = 0.70 e Å⁻³
Δρ_min = −0.78 e Å⁻³

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O6—H11⋯O4ⁱ	0.82	2.01	2.826 (3)	172
O6—H12⋯O3ⁱⁱ	0.82	2.07	2.879 (3)	168
O5—H10⋯O6	0.82	2.02	2.830 (3)	168
O5—H9⋯O6ⁱ	0.82	2.11	2.871 (3)	155
O4—H8⋯O3ⁱ	0.82	1.90	2.725 (3)	176
O4—H7⋯O2ⁱⁱⁱ	0.82	2.01	2.824 (3)	170
O1—H4⋯O2ⁱ	0.82	1.81	2.630 (2)	172
O1—H3⋯O5	0.82	1.88	2.697 (3)	174
Symmetry codes: (i) $[-x+{\script{1\over 2}}, -y+{\script{3\over 2}}, -z+1]$ ; (ii) $[-x+{\script{1\over 2}}, y+{\script{1\over 2}}, -z+{\script{1\over 2}}]$ ; (iii) $[-x+{\script{1\over 2}}, y+{\script{1\over 2}}, -z+{\script{3\over 2}}]$ .

Data collection: SMART (Bruker, 2005); cell refinement: SAINT (Bruker, 2005); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL.

Supporting information

Crystal structure: contains datablocks I, global. DOI: 10.1107/S1600536812014948/mw2062sup1.cif

Structure factors: contains datablock I. DOI: 10.1107/S1600536812014948/mw2062Isup2.hkl

checkCIF report

Comment top

Metal-organic frameworks have been widely studied over the past few decades owing to their important applications in gas storage, catalysis, sensing, nonlinear optics, magnetism, luminescence and ferroelectricity (Allendorf et al., 2009). Recently, the construction of hybrid framework materials using perfluorinated ligands has attracted much attention based on reports of interesting gas storage properties for such materials containing porous surfaces with exposed fluorine atoms (Yang et al., 2007). Tetrafluorosuccinic acid, as a perfluorinated dicarboxylate ligand, is an excellent candidate for the construction of hybrid frameworks with diverse structures (Hulvey et al., 2009) and with which the title compound, Cu(C₁₀H₈N₂)(H₂O)₄.C₄F₄O₄.4H₂O, was hydrothermally prepared from Cu(NO₃)₂.3H₂O and 4,4'-bipyridyl as coligand.

Both cation and anion have crystallographic 2-fold rotation symmetry with the 2-fold axes passing through Cu1, N1 and N2 and through the midpoint of the central C—C bond. The metal adopts a tetragonally elongated octahedral geometry because of the Jahn-Teller effect. The O4 atom occupies the elongated vertex with a Cu1—O4 distance of 2.462 (2) Å. The O1, N1 and N2 atoms occupy the equatorial plane with a Cu1—O1 distance of 1.976 (2) Å and Cu1—N1 and Cu1—N2 distances of 2.019 (3) and 2.027 (3) Å respectively (Figure 1). Adjacent Cu^II centers are bridged by 4,4'-bipy ligands to generate a one-dimensional linear chain structure parallel to the b axis. As shown in Figure 2 and Table 1, O—H···O hydrogen-bonding interactions between the cationic one-dimensional chains and the tetrafluorosuccinate anions and the free water molecules generate a three-dimensional supramolecular network.

Related literature top

For background to metal-organic framework structures, see: Allendorf et al., (2009). For the construction of hybrid frameworks with perfluorinated ligands, see: Yang et al. (2007); Hulvey et al. (2009).

Experimental top

A mixture of tetrafluorosuccinic acid (18.7 mg), 4,4'-bipyridyl (24.7 mg) and Cu(NO₃)₂.3H₂O (15.2 mg) was dissolved in water (8 ml) and stirred for 0.5 h at room temperature. It was then sealed in a 25 ml Teflon-lined stainless steel reactor and heated at 393 K for 48 h. Blue crystals suitable for X-ray analysis were obtained after cooling the solution to room temperature. The yield is ca 70% based on Cu²⁺.

Computing details top

Data collection: SMART (Bruker, 2005); cell refinement: SAINT (Bruker, 2005); data reduction: SAINT (Bruker, 2005); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).

Figures top

	Fig. 1. ORTEP drawing showing the coordination sphere of the Cu²⁺ center in the title compound with 50% probability displacement ellipsoids. Symmetry codes i: 1-x,y,1.5-z; ii: x,1+y,z; iii: x,1-y,z; iv: 0.5-z,0.5-y,1-z.
	Fig. 2. View down the c axis of the three-dimensional hydrogen bonding supramolecular network of the title compound.

catena-Poly[[[tetraaquacopper(II)]-µ-4,4'bipyridyl- κ²N:N'] tetrafluoridosuccinate tetrahydrate] top

Crystal data top

[Cu(C₁₀H₈N₂)(H₂O)₄](C₄F₄O₄)·4H₂O	F(000) = 1132
M_r = 551.89	D_x = 1.641 Mg m⁻³
Monoclinic, C2/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -C 2yc	Cell parameters from 8384 reflections
a = 17.112 (3) Å	θ = 3.0–27.4°
b = 11.135 (2) Å	µ = 1.07 mm⁻¹
c = 12.126 (2) Å	T = 298 K
β = 104.85 (3)°	Block, blue
V = 2233.3 (7) Å³	0.44 × 0.22 × 0.10 mm
Z = 4

Data collection top

Bruker SMART APEX diffractometer	2546 independent reflections
Radiation source: fine-focus sealed tube	2115 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.026
Detector resolution: 28 pixels mm^-1	θ_max = 27.4°, θ_min = 3.0°
ω scans	h = −22→21
Absorption correction: multi-scan (SADABS; Bruker, 2005)	k = −14→14
T_min = 0.650, T_max = 0.900	l = −15→15
10662 measured reflections

Refinement top

Refinement on F²	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F² > 2σ(F²)] = 0.027	H-atom parameters constrained
wR(F²) = 0.085	w = 1/[σ²(F_o²) + (0.0175P)² + 4.9756P] where P = (F_o² + 2F_c²)/3
S = 1.28	(Δ/σ)_max = 0.001
2546 reflections	Δρ_max = 0.70 e Å⁻³
153 parameters	Δρ_min = −0.78 e Å⁻³
0 restraints	Extinction correction: SHELXL97 (Sheldrick, 2008), Fc^*=kFc[1+0.001xFc²λ³/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.0077 (3)

Crystal data top

[Cu(C₁₀H₈N₂)(H₂O)₄](C₄F₄O₄)·4H₂O	V = 2233.3 (7) Å³
M_r = 551.89	Z = 4
Monoclinic, C2/c	Mo Kα radiation
a = 17.112 (3) Å	µ = 1.07 mm⁻¹
b = 11.135 (2) Å	T = 298 K
c = 12.126 (2) Å	0.44 × 0.22 × 0.10 mm
β = 104.85 (3)°

Data collection top

Bruker SMART APEX diffractometer	2546 independent reflections
Absorption correction: multi-scan (SADABS; Bruker, 2005)	2115 reflections with I > 2σ(I)
T_min = 0.650, T_max = 0.900	R_int = 0.026
10662 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.027	0 restraints
wR(F²) = 0.085	H-atom parameters constrained
S = 1.28	Δρ_max = 0.70 e Å⁻³
2546 reflections	Δρ_min = −0.78 e Å⁻³
153 parameters

Special details top

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

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > 2sigma(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
Cu1	0.5000	0.87438 (3)	0.7500	0.02173 (14)
F1	0.33513 (10)	0.31057 (16)	0.46607 (16)	0.0488 (5)
F2	0.29291 (11)	0.33959 (16)	0.61875 (14)	0.0457 (4)
O1	0.43960 (11)	0.87146 (15)	0.58758 (13)	0.0277 (4)
H3	0.4154	0.8089	0.5664	0.033*
H4	0.4087	0.9285	0.5680	0.033*
O2	0.16201 (13)	0.45430 (18)	0.49626 (16)	0.0426 (5)
O3	0.20898 (16)	0.4317 (2)	0.34192 (18)	0.0559 (7)
O4	0.36711 (11)	0.88591 (16)	0.79355 (15)	0.0307 (4)
H7	0.3579	0.8968	0.8561	0.037*
H8	0.3448	0.9399	0.7503	0.037*
O5	0.35115 (14)	0.6752 (2)	0.5062 (2)	0.0533 (6)
H9	0.3262	0.6610	0.5542	0.064*
H10	0.3197	0.7005	0.4479	0.064*
O6	0.23890 (14)	0.7923 (2)	0.32616 (18)	0.0540 (6)
H12	0.2530	0.8407	0.2843	0.065*
H11	0.2113	0.7397	0.2874	0.065*
N1	0.5000	0.6931 (2)	0.7500	0.0212 (6)
N2	0.5000	0.0563 (2)	0.7500	0.0231 (6)
C1	0.45882 (16)	0.6311 (2)	0.8111 (2)	0.0296 (5)
H1	0.4301	0.6731	0.8541	0.035*
C2	0.45722 (17)	0.5067 (2)	0.8129 (2)	0.0315 (6)
H2	0.4276	0.4668	0.8561	0.038*
C3	0.5000	0.4417 (3)	0.7500	0.0244 (7)
C4	0.5000	0.3076 (3)	0.7500	0.0246 (7)
C5	0.48432 (17)	0.2427 (2)	0.8399 (2)	0.0298 (6)
H5	0.4737	0.2827	0.9019	0.036*
C6	0.48451 (16)	0.1187 (2)	0.8369 (2)	0.0277 (5)
H6	0.4735	0.0766	0.8975	0.033*
C7	0.26765 (16)	0.3133 (2)	0.5056 (2)	0.0339 (6)
C8	0.20728 (18)	0.4103 (2)	0.4409 (2)	0.0363 (6)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Cu1	0.0336 (3)	0.01019 (19)	0.0216 (2)	0.000	0.00738 (16)	0.000
F1	0.0408 (10)	0.0482 (10)	0.0676 (12)	0.0108 (8)	0.0323 (9)	0.0130 (9)
F2	0.0502 (10)	0.0491 (10)	0.0327 (8)	0.0104 (8)	0.0014 (7)	0.0004 (7)
O1	0.0379 (10)	0.0199 (8)	0.0241 (8)	0.0054 (7)	0.0058 (7)	0.0010 (7)
O2	0.0532 (13)	0.0414 (11)	0.0369 (10)	0.0262 (10)	0.0185 (9)	0.0090 (9)
O3	0.0837 (17)	0.0539 (14)	0.0366 (11)	0.0379 (13)	0.0276 (11)	0.0198 (10)
O4	0.0366 (10)	0.0288 (9)	0.0296 (9)	0.0033 (8)	0.0135 (7)	0.0058 (7)
O5	0.0492 (13)	0.0590 (14)	0.0498 (13)	−0.0107 (11)	0.0090 (10)	−0.0077 (11)
O6	0.0659 (15)	0.0598 (14)	0.0361 (11)	−0.0240 (12)	0.0125 (10)	−0.0009 (10)
N1	0.0260 (14)	0.0129 (12)	0.0245 (13)	0.000	0.0063 (11)	0.000
N2	0.0333 (16)	0.0125 (12)	0.0273 (14)	0.000	0.0145 (12)	0.000
C1	0.0395 (14)	0.0167 (11)	0.0392 (13)	0.0029 (10)	0.0224 (11)	−0.0002 (10)
C2	0.0433 (16)	0.0166 (11)	0.0427 (14)	−0.0001 (10)	0.0260 (12)	0.0033 (10)
C3	0.0317 (18)	0.0126 (14)	0.0307 (17)	0.000	0.0115 (14)	0.000
C4	0.0319 (18)	0.0121 (14)	0.0325 (17)	0.000	0.0130 (14)	0.000
C5	0.0484 (16)	0.0163 (11)	0.0303 (13)	−0.0009 (10)	0.0206 (11)	−0.0027 (9)
C6	0.0429 (15)	0.0178 (11)	0.0282 (12)	0.0002 (10)	0.0194 (11)	0.0016 (9)
C7	0.0338 (14)	0.0386 (15)	0.0323 (13)	0.0102 (12)	0.0140 (11)	0.0063 (11)
C8	0.0484 (17)	0.0291 (13)	0.0312 (13)	0.0147 (12)	0.0101 (12)	0.0082 (11)

Geometric parameters (Å, º) top

Cu1—O1ⁱ	1.9760 (17)	N1—C1	1.338 (3)
Cu1—O1	1.9761 (17)	N2—C6	1.344 (3)
Cu1—N1	2.018 (3)	N2—C6ⁱ	1.344 (3)
Cu1—N2ⁱⁱ	2.025 (3)	N2—Cu1ⁱⁱⁱ	2.025 (3)
F1—C7	1.360 (3)	C1—C2	1.386 (3)
F2—C7	1.360 (3)	C1—H1	0.9300
O1—H3	0.8180	C2—C3	1.388 (3)
O1—H4	0.8212	C2—H2	0.9300
O2—C8	1.248 (3)	C3—C2ⁱ	1.388 (3)
O3—C8	1.232 (3)	C3—C4	1.494 (4)
O4—H7	0.8224	C4—C5	1.390 (3)
O4—H8	0.8241	C4—C5ⁱ	1.390 (3)
O5—H9	0.8196	C5—C6	1.382 (3)
O5—H10	0.8200	C5—H5	0.9300
O6—H12	0.8182	C6—H6	0.9300
O6—H11	0.8207	C7—C7^iv	1.525 (6)
N1—C1ⁱ	1.338 (3)	C7—C8	1.560 (4)

O1ⁱ—Cu1—O1	178.11 (10)	C3—C2—H2	120.1
O1ⁱ—Cu1—N1	89.06 (5)	C2—C3—C2ⁱ	117.2 (3)
O1—Cu1—N1	89.06 (5)	C2—C3—C4	121.38 (15)
O1ⁱ—Cu1—N2ⁱⁱ	90.94 (5)	C2ⁱ—C3—C4	121.38 (15)
O1—Cu1—N2ⁱⁱ	90.94 (5)	C5—C4—C5ⁱ	117.4 (3)
N1—Cu1—N2ⁱⁱ	180.000 (1)	C5—C4—C3	121.31 (15)
Cu1—O1—H3	114.9	C5ⁱ—C4—C3	121.30 (15)
Cu1—O1—H4	114.1	C6—C5—C4	119.8 (2)
H3—O1—H4	109.3	C6—C5—H5	120.1
H7—O4—H8	108.2	C4—C5—H5	120.1
H9—O5—H10	109.4	N2—C6—C5	122.6 (2)
H12—O6—H11	109.5	N2—C6—H6	118.7
C1ⁱ—N1—C1	117.8 (3)	C5—C6—H6	118.7
C1ⁱ—N1—Cu1	121.09 (14)	F1—C7—F2	106.3 (2)
C1—N1—Cu1	121.09 (14)	F1—C7—C7^iv	107.5 (3)
C6—N2—C6ⁱ	117.8 (3)	F2—C7—C7^iv	107.8 (3)
C6—N2—Cu1ⁱⁱⁱ	121.12 (14)	F1—C7—C8	110.5 (2)
C6ⁱ—N2—Cu1ⁱⁱⁱ	121.12 (14)	F2—C7—C8	110.9 (2)
N1—C1—C2	122.7 (2)	C7^iv—C7—C8	113.5 (3)
N1—C1—H1	118.7	O3—C8—O2	128.4 (3)
C2—C1—H1	118.7	O3—C8—C7	116.5 (2)
C1—C2—C3	119.8 (2)	O2—C8—C7	115.1 (2)
C1—C2—H2	120.1

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

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
O6—H11···O4^v	0.82	2.01	2.826 (3)	172
O6—H12···O3^vi	0.82	2.07	2.879 (3)	168
O5—H10···O6	0.82	2.02	2.830 (3)	168
O5—H9···O6^v	0.82	2.11	2.871 (3)	155
O4—H8···O3^v	0.82	1.90	2.725 (3)	176
O4—H7···O2^vii	0.82	2.01	2.824 (3)	170
O1—H4···O2^v	0.82	1.81	2.630 (2)	172
O1—H3···O5	0.82	1.88	2.697 (3)	174

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

Experimental details

Crystal data
Chemical formula	[Cu(C₁₀H₈N₂)(H₂O)₄](C₄F₄O₄)·4H₂O
M_r	551.89
Crystal system, space group	Monoclinic, C2/c
Temperature (K)	298
a, b, c (Å)	17.112 (3), 11.135 (2), 12.126 (2)
β (°)	104.85 (3)
V (Å³)	2233.3 (7)
Z	4
Radiation type	Mo Kα
µ (mm⁻¹)	1.07
Crystal size (mm)	0.44 × 0.22 × 0.10

Data collection
Diffractometer	Bruker SMART APEX diffractometer
Absorption correction	Multi-scan (SADABS; Bruker, 2005)
T_min, T_max	0.650, 0.900
No. of measured, independent and observed [I > 2σ(I)] reflections	10662, 2546, 2115
R_int	0.026
(sin θ/λ)_max (Å⁻¹)	0.647

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.027, 0.085, 1.28
No. of reflections	2546
No. of parameters	153
H-atom treatment	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	0.70, −0.78

Computer programs: SMART (Bruker, 2005), SAINT (Bruker, 2005), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), SHELXTL (Sheldrick, 2008).

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
O6—H11···O4ⁱ	0.82	2.01	2.826 (3)	172
O6—H12···O3ⁱⁱ	0.82	2.07	2.879 (3)	168
O5—H10···O6	0.82	2.02	2.830 (3)	168
O5—H9···O6ⁱ	0.82	2.11	2.871 (3)	155
O4—H8···O3ⁱ	0.82	1.90	2.725 (3)	176
O4—H7···O2ⁱⁱⁱ	0.82	2.01	2.824 (3)	170
O1—H4···O2ⁱ	0.82	1.81	2.630 (2)	172
O1—H3···O5	0.82	1.88	2.697 (3)	174

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

Acknowledgements

This work was supported by the National Natural Science Foundation of China (21071087) and the K. C. Wong Magna Fund in Ningbo University.

References

Allendorf, M. D., Bauer, C. A., Bhakta, R. K. & Houk, R. J. (2009). Chem. Soc. Rev. 38, 1330–1352. Web of Science CrossRef PubMed CAS Google Scholar
Bruker (2005). SMART, SAINT and SADABS. Bruker AXS Inc., Madison, Wisconsin, USA. Google Scholar
Hulvey, Z., Ayala, E., Furman, J. D., Forster, P. M. & Cheetham, A. K. (2009). Cryst. Growth Des. 9, 4759–4765. Web of Science CSD CrossRef CAS Google Scholar
Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122. Web of Science CrossRef CAS IUCr Journals Google Scholar
Yang, C., Wang, X.-P. & Omary, M. A. (2007). J. Am. Chem. Soc. 129, 15454–15455. Web of Science CSD CrossRef PubMed CAS Google Scholar

This is an open-access article distributed under the terms of the Creative Commons Attribution (CC-BY) Licence, which permits unrestricted use, distribution, and reproduction in any medium, provided the original authors and source are cited.