Supporting information
Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270109024500/fg3104sup1.cif | |
Structure factor file (CIF format) https://doi.org/10.1107/S0108270109024500/fg3104Isup2.hkl |
CCDC reference: 746044
Complex (I), [Co(C5H9N)4(H2O)2](ClO4)2, initially reported as [Co(C5H9N)4H2O](ClO4)2, was synthesized and routinely characterized by Becker and co-workers (Becker et al., 1986; Becker, 1993), by reaction of excess and/or stoichiometric amounts of CNCMe3 with Co(ClO4)2.6H2O in ethanol solution (94% yield). The complex can be recrystallized from CH3CN and diethyl ether (85% recovery) [m.p. 383–385 K (decomposition)]. X-ray quality crystals of (I) were obtained by slow diffusion of Et2O into a CH3CN solution at room temperature. Elemental analysis, calculated for C20H40Cl2CoN4O10: C 38.35, H 6.44, N 8.94, Cl 11.32%; found: C 37.89, H 6.47, N 8.94, Cl 11.64%. IR spectrum (Nujol mull, ν, cm-1): –N≡C 2214 (vs), ~2185 (vw, sh), 2031 (w); O—H 3448 (s), ~3500 (m, sh); diffuse reflectance electronic spectrum (nm): ~814 (br, A = 0.289), ~ 525 (s, h), 462 (0.338), ~276 (s, h), 263 (1.54), 216 (1.32); magnetic susceptibility: χg = 3.74 (7) × 10-6 cgs, µeff = 2.52 (5) BM.
All H atoms were refined using a riding model, with C—H = 0.98Å and O—H = 0.95 Å, and with Uiso(H) = 1.5Ueq(C) or 1.5Ueq(O). Perchlorate disorder was apparent in the structure, hence atoms O3A and O3B, and atoms O4A and O4B, were refined with complementary occupancies, respectively.
Reactions of CoII perchlorate with alkyl isocyanide ligands have been shown to produce metal–metal bonded diamagnetic dimeric complexes in the solid state, of general formula [Co2(CNR)10](ClO4)4 and maroon–red in colour, dissociating into dark-blue one-electron paramagnetic monomeric complexes in solution. The crystallographic structure of [(MeNC)5Co—Co(CNMe)5](ClO4)4 has been determined (Cotton et al., 1964), and structures with CNR = CNEt (Boorman et al., 1970), CNCHMe2 (Becker, 1993) and CNCH2Ph (Becker & Malete, 2003) were assumed to be analogous. Complexes with CNR = CNC4H9-n and CNC6H11 (Becker, 1993, 1994) have not been satisfactorily isolated, but appear to exhibit analogous behaviour. The t-butyl isocyanide ligand (CNCMe3), however, has been unique in forming low-spin monomeric CoII complexes with only four alkyl isocyanide ligands (Becker et al., 1986; Becker, 1993). Even recent work with the t-octyl isocyanide ligand (CNC8H17-t, i.e. 1,1,3,3-tetramethylbutyl isocyanide) has also produced low-spin monomeric CoII complexes but with the usual 5:1 alkyl isocyanide:CoII mole ratio, i.e. [Co(CNC8H17-t)5](ClO4)2 and [Co(CNC8H17-t)5](BF4)2.2H2O (Becker et al., 2008). The unique composition of the title complex, (I), especially when initially reported as [Co(CNCMe3)4H2O](ClO4)2, prompted a crystallographic investigation to determine if possible aspects such as steric crowding of the relatively bulky t-butyl isocyanide ligands or unusually strong coordination of the water molecule(s) may be favouring this particular stereochemistry.
Compound (I) is observed to crystallize in the monoclinic space group C2/m. The molecular structure is shown in Figs. 1 and 2. The CoII atom is at a site with point-group symmetry of 2/m (C2h) and is at the centre of a rectangular bipyramid. The CoC4 moiety is strictly planar, with the linear O—Co—O C2 axis perpendicular to this plane, but the two non-equivalent Co—C bonds [1.900 (3) and 1.911 (3) Å] form a rectangular, but not square, plane, with the unique C—Co—C bond angle being 86.83 (11)°. The Co—C bond lengths are sufficiently short to justify the dπ→ π* back-bonding expected from organoisocyanide ligands, and the C≡N bonds [both 1.141 (4) Å] are just slightly shorter than that in the free C≡NCH3 molecule (1.166 Å; Costain, 1958). The Co—C≡N and C≡N—C bond angles average 175.5 (4)°, approximately equal to, but slightly less than, the theoretically expected 180.0°.
The unique coordinated water molecule is so orientated that the H atoms are only 15° staggered from being directly over the Co—C1 bonds, i.e. the shorter Co—C bonds. The H-atom placements of the coordinated water were constrained according to interatomic attraction. These assigned locations are probably the result of attraction to the perchlorate anions, rather than any interaction with the Co—C≡N bonds. The unique water H atom takes part in an O—H···O hydrogen bond with an adjacent perchlorate atom O2, with dimensions H1W···O2 = 2.04 Å, O1···O2 = 2.993 (5) Å and O1—H1W···O2 180°, leading to an infinite hydrogen-bond chain in the b direction, as shown in Fig. 2. The perchlorate ion is disordered, as is not atypical for these anions.
Many known structures for CNCMe3 complexes with cobalt are for multiple mixed-ligand complexes, usually of CoI or CoIII. Compounds most relevant for comparison with (I) would appear to be the other CoII complexes of the form [Co(CNPh)5](ClO4)2.0.5ClCH2CH2Cl, especially when viewed as [Co(CNPh)5ClO4]ClO4.0.5ClCH2CH2Cl, (II) (Jurnak et al., 1975), [Co(CNC6H4Me-p)4I2], (III) (Gilmore et al., 1969), [Co(CNC6H3Et2-2,6)4(ClO4)2], (IV) (Becker & Cooper, 1991), [Co(CNC6H4CO2Me-4)4I2], (V) (Squires & Mayr, 1997), trans-[Co(CNC6H4OSiMe3-2)4I2], (VI) (Hahn & Lügger, 1994), and trans-[Co(CNC6H2iPr2-2,6-4-C≡ CH)4I2], (VII) (Lu et al., 1999). Structural comparisons based on these compounds are shown in Table 1.
The Co—O bond length of 2.245 (2) Å is definitely rather long, since a Co—O single-bond length of about 1.97 Å should be expected (Slade et al., 1971), although this bond is known over the rather wide range of about 1.75–2.40 Å, with 1.85–2.20 Å being most common (Cambridge Structural Database, 2009 [Specific release?]; Allen, 2002). However, the Co—I bonds in (III), (V), (VI) and (VII) are also consistently elongated, while the Co—O bond in (IV), i.e. 2.266 (7) Å, would be considered long, albeit short for a coordinated perchlorate bond. In none of the CoII complexes considered does it appear that the CoC4 moiety is actually square-planar. The CoC4 unit may be planar, having equal [(VII)] or unequal [(IV), (V) or (VI)] Co—C bond lengths, but is also has unequal C—Co—C bond angles, i.e. forming a rectangular plane. Alternatively, as in (III), there is a C2/S4 axis because alternating Co—C bonds are bent above and below the Co centre (~5°). Complex (IV) would appear to approximate most closely the coordination structure for [Co(CNCMe3)4(H2O)2]2+.
Once tetragonal coordination is recognized for (I), analogy with addition complexes of selected nitrogen bases, [Co(CNCMe3)4L2](ClO4)2 (Becker, 1992), becomes apparent. The N-base complexes are blue in colour, due to a crystal field band at 630–670 nm, while (I) is beige to flesh-coloured [Please be more specific - an objective colour is required], with a comparable band at 814 nm. This underscores the higher position in the spectrochemical series of N-ligands over O-ligands (Wulfsberg, 2000). However, the diffuse reflectance electronic spectrum for (IV) (λmax = 875 nm; Becker & Cooper, 1991) is similar to that for (I).
The coordination structure in (I), [Co(CNCMe3)4(H2O)2](ClO4), has thus been shown to be analogous to known [Co(CNR)4X2] complexes with aryl isocyanide ligands. The t-butyl substituents are not seen to be sterically crowded to the extent of precluding coordination of a fifth alkyl isocyanide ligand, and the relatively long Co—O bond lengths contradict the possibility of particularly strong water-molecule coordination, so except for a rather unconvincing argument of strong hydrogen bonding between the coordinated water molecules and the anionic perchlorates, there appears to be no crystallographic explanation as to why a dimeric structure, or at least pentakis-alkyl isocyanide coordination, has not been observed for the title complex.
Data collection: APEX2 (Bruker, 2005); cell refinement: SAINT-NT (Bruker, 2005); data reduction: SAINT-NT (Bruker, 2005); program(s) used to solve structure: SHELXTL (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997) and DIAMOND (Brandenburg, 1997); software used to prepare material for publication: WinGX (Farrugia, 1999) and PLATON (Spek, 2009).
[Co(C5H9N)4(H2O)2](ClO4)2 | F(000) = 658 |
Mr = 626.39 | Dx = 1.38 Mg m−3 |
Monoclinic, C2/m | Mo Kα radiation, λ = 0.71073 Å |
Hall symbol: -C 2y | Cell parameters from 5327 reflections |
a = 15.830 (1) Å | θ = 2.6–28.3° |
b = 8.1176 (5) Å | µ = 0.80 mm−1 |
c = 13.8319 (9) Å | T = 173 K |
β = 122.013 (1)° | Block, brown |
V = 1507.12 (17) Å3 | 0.73 × 0.33 × 0.08 mm |
Z = 2 |
Bruker APEXII CCD area-detector diffractometer | 1867 reflections with I > 2σ(I) |
φ and ω scans | Rint = 0.018 |
Absorption correction: integration (XPREP; Bruker, 1999) | θmax = 28°, θmin = 1.7° |
Tmin = 0.595, Tmax = 0.939 | h = −20→20 |
6901 measured reflections | k = −10→10 |
1949 independent reflections | l = −16→18 |
Refinement on F2 | 30 restraints |
Least-squares matrix: full | H-atom parameters constrained |
R[F2 > 2σ(F2)] = 0.039 | w = 1/[σ2(Fo2) + (0.0579P)2 + 3.0958P] where P = (Fo2 + 2Fc2)/3 |
wR(F2) = 0.106 | (Δ/σ)max < 0.001 |
S = 1.04 | Δρmax = 0.72 e Å−3 |
1949 reflections | Δρmin = −0.88 e Å−3 |
112 parameters |
[Co(C5H9N)4(H2O)2](ClO4)2 | V = 1507.12 (17) Å3 |
Mr = 626.39 | Z = 2 |
Monoclinic, C2/m | Mo Kα radiation |
a = 15.830 (1) Å | µ = 0.80 mm−1 |
b = 8.1176 (5) Å | T = 173 K |
c = 13.8319 (9) Å | 0.73 × 0.33 × 0.08 mm |
β = 122.013 (1)° |
Bruker APEXII CCD area-detector diffractometer | 1949 independent reflections |
Absorption correction: integration (XPREP; Bruker, 1999) | 1867 reflections with I > 2σ(I) |
Tmin = 0.595, Tmax = 0.939 | Rint = 0.018 |
6901 measured reflections |
R[F2 > 2σ(F2)] = 0.039 | 30 restraints |
wR(F2) = 0.106 | H-atom parameters constrained |
S = 1.04 | Δρmax = 0.72 e Å−3 |
1949 reflections | Δρmin = −0.88 e Å−3 |
112 parameters |
Experimental. Numerical integration absorption corrections based on indexed crystal faces were applied using the XPREP routine (Bruker, 1999) |
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 | Occ. (<1) | |
C1 | 0.6396 (2) | 0.5 | 0.5621 (2) | 0.0200 (5) | |
C2 | 0.83352 (19) | 0.5 | 0.6665 (2) | 0.0219 (5) | |
C3 | 0.8722 (2) | 0.5 | 0.7937 (3) | 0.0296 (6) | |
H3A | 0.848 | 0.5984 | 0.8126 | 0.044* | 0.5 |
H3B | 0.9452 | 0.5003 | 0.8375 | 0.044* | |
H3C | 0.8482 | 0.4013 | 0.8127 | 0.044* | 0.5 |
C4 | 0.86394 (15) | 0.6558 (3) | 0.63079 (19) | 0.0310 (5) | |
H4A | 0.8325 | 0.6566 | 0.5478 | 0.047* | |
H4B | 0.9365 | 0.658 | 0.6674 | 0.047* | |
H4C | 0.8424 | 0.7528 | 0.6543 | 0.047* | |
C5 | 0.53119 (19) | 0.5 | 0.6537 (2) | 0.0203 (5) | |
C6 | 0.6022 (2) | 0.5 | 0.8727 (2) | 0.0225 (5) | |
C7 | 0.56749 (19) | 0.3448 (3) | 0.90333 (19) | 0.0358 (5) | |
H7A | 0.4948 | 0.347 | 0.8659 | 0.054* | |
H7B | 0.5981 | 0.3396 | 0.9862 | 0.054* | |
H7C | 0.5872 | 0.2478 | 0.8777 | 0.054* | |
C8 | 0.7144 (2) | 0.5 | 0.9255 (3) | 0.0365 (8) | |
H8A | 0.7337 | 0.4011 | 0.9012 | 0.055* | 0.5 |
H8B | 0.748 | 0.5006 | 1.0088 | 0.055* | |
H8C | 0.7337 | 0.5983 | 0.9006 | 0.055* | 0.5 |
O1 | 0.5 | 0.7765 (3) | 0.5 | 0.0300 (5) | |
H1W | 0.556 | 0.8475 | 0.5392 | 0.045* | |
Co1 | 0.5 | 0.5 | 0.5 | 0.01634 (16) | |
N1 | 0.72436 (17) | 0.5 | 0.6058 (2) | 0.0221 (5) | |
N2 | 0.55687 (18) | 0.5 | 0.7479 (2) | 0.0226 (5) | |
Cl1 | 0.70949 (5) | 1 | 0.73994 (6) | 0.0280 (2) | |
O2 | 0.6765 (2) | 1.0001 (8) | 0.62335 (9) | 0.0992 (18) | |
O3A | 0.6758 (6) | 0.8631 (6) | 0.7661 (5) | 0.138 (3) | 0.737 (11) |
O4A | 0.81225 (5) | 1.0001 (12) | 0.8031 (2) | 0.101 (3) | 0.737 (11) |
O4B | 0.62531 (17) | 0.9998 (11) | 0.7481 (3) | 0.123 (8) | 0.263 (11) |
O3B | 0.7616 (6) | 0.8692 (6) | 0.7970 (5) | 0.110 (6) | 0.263 (11) |
U11 | U22 | U33 | U12 | U13 | U23 | |
C1 | 0.0194 (12) | 0.0244 (13) | 0.0167 (11) | 0 | 0.0099 (10) | 0 |
C2 | 0.0120 (11) | 0.0317 (14) | 0.0205 (12) | 0 | 0.0077 (10) | 0 |
C3 | 0.0238 (13) | 0.0422 (17) | 0.0209 (13) | 0 | 0.0106 (11) | 0 |
C4 | 0.0239 (10) | 0.0379 (12) | 0.0303 (11) | −0.0062 (8) | 0.0137 (9) | 0.0013 (9) |
C5 | 0.0165 (11) | 0.0248 (13) | 0.0189 (12) | 0 | 0.0090 (10) | 0 |
C6 | 0.0230 (13) | 0.0311 (14) | 0.0118 (11) | 0 | 0.0082 (10) | 0 |
C7 | 0.0445 (13) | 0.0390 (12) | 0.0233 (10) | −0.0079 (10) | 0.0176 (10) | 0.0030 (9) |
C8 | 0.0239 (14) | 0.061 (2) | 0.0208 (14) | 0 | 0.0089 (12) | 0 |
O1 | 0.0261 (10) | 0.0256 (11) | 0.0326 (11) | 0 | 0.0117 (9) | 0 |
Co1 | 0.0118 (2) | 0.0250 (3) | 0.0113 (2) | 0 | 0.00546 (19) | 0 |
N1 | 0.0160 (11) | 0.0271 (12) | 0.0228 (11) | 0 | 0.0100 (9) | 0 |
N2 | 0.0231 (11) | 0.0281 (12) | 0.0158 (11) | 0 | 0.0097 (9) | 0 |
Cl1 | 0.0298 (4) | 0.0300 (4) | 0.0181 (3) | 0 | 0.0085 (3) | 0 |
O2 | 0.075 (3) | 0.196 (6) | 0.0235 (15) | 0 | 0.0235 (16) | 0 |
O3A | 0.204 (7) | 0.096 (4) | 0.155 (5) | −0.080 (4) | 0.123 (5) | −0.006 (3) |
O4A | 0.036 (2) | 0.188 (8) | 0.051 (3) | 0 | 0.005 (2) | 0 |
O4B | 0.076 (9) | 0.167 (14) | 0.146 (13) | 0 | 0.073 (9) | 0 |
O3B | 0.155 (10) | 0.068 (7) | 0.056 (6) | 0.071 (7) | 0.021 (6) | 0.024 (5) |
C1—N1 | 1.142 (4) | C7—H7A | 0.98 |
C1—Co1 | 1.900 (3) | C7—H7B | 0.98 |
C2—N1 | 1.467 (3) | C7—H7C | 0.98 |
C2—C4 | 1.525 (3) | C8—H8A | 0.98 |
C2—C4i | 1.525 (3) | C8—H8B | 0.98 |
C2—C3 | 1.527 (4) | C8—H8C | 0.98 |
C3—H3A | 0.98 | O1—Co1 | 2.245 (2) |
C3—H3B | 0.98 | O1—H1W | 0.95 |
C3—H3C | 0.98 | Co1—C1ii | 1.900 (3) |
C4—H4A | 0.98 | Co1—C5ii | 1.911 (3) |
C4—H4B | 0.98 | Co1—O1ii | 2.245 (2) |
C4—H4C | 0.98 | Cl1—O3Biii | 1.320 (8) |
C5—N2 | 1.141 (4) | Cl1—O3B | 1.3196 |
C5—Co1 | 1.911 (3) | Cl1—O3Aiii | 1.363 (7) |
C6—N2 | 1.476 (3) | Cl1—O3A | 1.3628 |
C6—C8 | 1.521 (4) | Cl1—O4A | 1.3794 |
C6—C7i | 1.522 (3) | Cl1—O4B | 1.3959 |
C6—C7 | 1.522 (3) | Cl1—O2 | 1.4074 |
N1—C1—Co1 | 175.8 (2) | C1ii—Co1—C1 | 180.00 (16) |
N1—C2—C4 | 107.04 (15) | C1ii—Co1—C5ii | 86.83 (11) |
N1—C2—C4i | 107.04 (15) | C1—Co1—C5ii | 93.17 (11) |
C4—C2—C4i | 112.0 (2) | C1ii—Co1—C5 | 93.17 (11) |
N1—C2—C3 | 106.9 (2) | C1—Co1—C5 | 86.83 (11) |
C4—C2—C3 | 111.75 (15) | C5ii—Co1—C5 | 180.0000 (10) |
C4i—C2—C3 | 111.75 (15) | C1ii—Co1—O1 | 90 |
C2—C3—H3A | 109.5 | C1—Co1—O1 | 90 |
C2—C3—H3B | 109.5 | C5ii—Co1—O1 | 90 |
H3A—C3—H3B | 109.5 | C5—Co1—O1 | 90 |
C2—C3—H3C | 109.5 | C1ii—Co1—O1ii | 90 |
H3A—C3—H3C | 109.5 | C1—Co1—O1ii | 90 |
H3B—C3—H3C | 109.5 | C5ii—Co1—O1ii | 90 |
C2—C4—H4A | 109.5 | C5—Co1—O1ii | 90 |
C2—C4—H4B | 109.5 | O1—Co1—O1ii | 180 |
H4A—C4—H4B | 109.5 | C1—N1—C2 | 177.7 (3) |
C2—C4—H4C | 109.5 | C5—N2—C6 | 173.3 (3) |
H4A—C4—H4C | 109.5 | O3Biii—Cl1—O3B | 107.2 (3) |
H4B—C4—H4C | 109.5 | O3Biii—Cl1—O3Aiii | 52.66 (16) |
N2—C5—Co1 | 175.1 (2) | O3B—Cl1—O3Aiii | 134.92 (12) |
N2—C6—C8 | 106.4 (2) | O3Biii—Cl1—O3A | 134.92 (15) |
N2—C6—C7i | 107.60 (15) | O3B—Cl1—O3A | 52.7 |
C8—C6—C7i | 111.59 (16) | O3Aiii—Cl1—O3A | 109.3 (2) |
N2—C6—C7 | 107.60 (15) | O3Biii—Cl1—O4A | 57.8 (2) |
C8—C6—C7 | 111.59 (16) | O3B—Cl1—O4A | 57.9 |
C7i—C6—C7 | 111.8 (3) | O3Aiii—Cl1—O4A | 109.14 (11) |
C6—C7—H7A | 109.5 | O3A—Cl1—O4A | 109.2 |
C6—C7—H7B | 109.5 | O3Biii—Cl1—O4B | 105.88 (10) |
H7A—C7—H7B | 109.5 | O3B—Cl1—O4B | 105.7 |
C6—C7—H7C | 109.5 | O3Aiii—Cl1—O4B | 56.9 (2) |
H7A—C7—H7C | 109.5 | O3A—Cl1—O4B | 56.8 |
H7B—C7—H7C | 109.5 | O4A—Cl1—O4B | 143.6 |
C6—C8—H8A | 109.5 | O3Biii—Cl1—O2 | 114.80 (17) |
C6—C8—H8B | 109.5 | O3B—Cl1—O2 | 114.9 |
H8A—C8—H8B | 109.5 | O3Aiii—Cl1—O2 | 110.14 (11) |
C6—C8—H8C | 109.5 | O3A—Cl1—O2 | 110.2 |
H8A—C8—H8C | 109.5 | O4A—Cl1—O2 | 108.8 |
H8B—C8—H8C | 109.5 | O4B—Cl1—O2 | 107.6 |
Co1—O1—H1W | 127.3 |
Symmetry codes: (i) x, −y+1, z; (ii) −x+1, −y+1, −z+1; (iii) x, −y+2, z. |
Experimental details
Crystal data | |
Chemical formula | [Co(C5H9N)4(H2O)2](ClO4)2 |
Mr | 626.39 |
Crystal system, space group | Monoclinic, C2/m |
Temperature (K) | 173 |
a, b, c (Å) | 15.830 (1), 8.1176 (5), 13.8319 (9) |
β (°) | 122.013 (1) |
V (Å3) | 1507.12 (17) |
Z | 2 |
Radiation type | Mo Kα |
µ (mm−1) | 0.80 |
Crystal size (mm) | 0.73 × 0.33 × 0.08 |
Data collection | |
Diffractometer | Bruker APEXII CCD area-detector |
Absorption correction | Integration (XPREP; Bruker, 1999) |
Tmin, Tmax | 0.595, 0.939 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 6901, 1949, 1867 |
Rint | 0.018 |
(sin θ/λ)max (Å−1) | 0.661 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.039, 0.106, 1.04 |
No. of reflections | 1949 |
No. of parameters | 112 |
No. of restraints | 30 |
H-atom treatment | H-atom parameters constrained |
Δρmax, Δρmin (e Å−3) | 0.72, −0.88 |
Computer programs: APEX2 (Bruker, 2005), SAINT-NT (Bruker, 2005), SHELXTL (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), ORTEP-3 for Windows (Farrugia, 1997) and DIAMOND (Brandenburg, 1997), WinGX (Farrugia, 1999) and PLATON (Spek, 2009).
Compound | Co—C | C≡N | Co—C≡N | C≡N-C | |
(I) | 1.900 (3) | 1.911 (3) | 1.141 (4)–1.142 (4) | 175.8 (2)–175.1 (2) | 177.7 (3)–173.3 (3) |
(II) | 1.84 (2) | 1.16 (1) | 174.6 (6) | 173.5 (10)–179.0 (13) | |
(III) | 1.81 (4) | 1.14 (4) | 178.8 (42) | 174.4 (40) | |
(IV) | 1.896 (9) | 1.887 (9) | 1.152 (12) | 175.3 (7) | 174.0 (7)–177.2 (9) |
(V) | 1.865 (10) | 1.835 (15) | 1.15 (3) | 173 (1)–178 (1) | 166 (1)–178 (1) |
(VI) | 1.858 (2) | 1.866 (2) | 1.148 (3)–1.137 (3) | 175.9 (2)–174.6 (2) | 174.7 (2)–173.6 (2) |
(VII) | 1.850 (7) | 1.139 (7) | 175.6 (6) |
References: (I), [Co(CNCMe3)4(H2O)2](ClO4)2 (this work); (II), [Co(CNPh)5ClO4]ClO4.0.5ClCH2CH2Cl (Jurnak et al., 1975); (III), Co(CNC6H4Me-p)4I2] (Gilmore et al., 1969); (IV), [Co(C6H3Et2-2,6)4(ClO4)2] (Becker & Cooper, 1991); (V), [Co(CNC6H4CO2Me-4)2I2] (Squires & Mayr, 1997); (VI), [Co(CNC6H4OSiMe3-2)4I2] (Hahn & Lügger, 1994); (VII), [Co(CNC6H2iPr2-2,6-4-C≡CH)4I2] (Lu et al., 1999). |
Reactions of CoII perchlorate with alkyl isocyanide ligands have been shown to produce metal–metal bonded diamagnetic dimeric complexes in the solid state, of general formula [Co2(CNR)10](ClO4)4 and maroon–red in colour, dissociating into dark-blue one-electron paramagnetic monomeric complexes in solution. The crystallographic structure of [(MeNC)5Co—Co(CNMe)5](ClO4)4 has been determined (Cotton et al., 1964), and structures with CNR = CNEt (Boorman et al., 1970), CNCHMe2 (Becker, 1993) and CNCH2Ph (Becker & Malete, 2003) were assumed to be analogous. Complexes with CNR = CNC4H9-n and CNC6H11 (Becker, 1993, 1994) have not been satisfactorily isolated, but appear to exhibit analogous behaviour. The t-butyl isocyanide ligand (CNCMe3), however, has been unique in forming low-spin monomeric CoII complexes with only four alkyl isocyanide ligands (Becker et al., 1986; Becker, 1993). Even recent work with the t-octyl isocyanide ligand (CNC8H17-t, i.e. 1,1,3,3-tetramethylbutyl isocyanide) has also produced low-spin monomeric CoII complexes but with the usual 5:1 alkyl isocyanide:CoII mole ratio, i.e. [Co(CNC8H17-t)5](ClO4)2 and [Co(CNC8H17-t)5](BF4)2.2H2O (Becker et al., 2008). The unique composition of the title complex, (I), especially when initially reported as [Co(CNCMe3)4H2O](ClO4)2, prompted a crystallographic investigation to determine if possible aspects such as steric crowding of the relatively bulky t-butyl isocyanide ligands or unusually strong coordination of the water molecule(s) may be favouring this particular stereochemistry.
Compound (I) is observed to crystallize in the monoclinic space group C2/m. The molecular structure is shown in Figs. 1 and 2. The CoII atom is at a site with point-group symmetry of 2/m (C2h) and is at the centre of a rectangular bipyramid. The CoC4 moiety is strictly planar, with the linear O—Co—O C2 axis perpendicular to this plane, but the two non-equivalent Co—C bonds [1.900 (3) and 1.911 (3) Å] form a rectangular, but not square, plane, with the unique C—Co—C bond angle being 86.83 (11)°. The Co—C bond lengths are sufficiently short to justify the dπ→ π* back-bonding expected from organoisocyanide ligands, and the C≡N bonds [both 1.141 (4) Å] are just slightly shorter than that in the free C≡NCH3 molecule (1.166 Å; Costain, 1958). The Co—C≡N and C≡N—C bond angles average 175.5 (4)°, approximately equal to, but slightly less than, the theoretically expected 180.0°.
The unique coordinated water molecule is so orientated that the H atoms are only 15° staggered from being directly over the Co—C1 bonds, i.e. the shorter Co—C bonds. The H-atom placements of the coordinated water were constrained according to interatomic attraction. These assigned locations are probably the result of attraction to the perchlorate anions, rather than any interaction with the Co—C≡N bonds. The unique water H atom takes part in an O—H···O hydrogen bond with an adjacent perchlorate atom O2, with dimensions H1W···O2 = 2.04 Å, O1···O2 = 2.993 (5) Å and O1—H1W···O2 180°, leading to an infinite hydrogen-bond chain in the b direction, as shown in Fig. 2. The perchlorate ion is disordered, as is not atypical for these anions.
Many known structures for CNCMe3 complexes with cobalt are for multiple mixed-ligand complexes, usually of CoI or CoIII. Compounds most relevant for comparison with (I) would appear to be the other CoII complexes of the form [Co(CNPh)5](ClO4)2.0.5ClCH2CH2Cl, especially when viewed as [Co(CNPh)5ClO4]ClO4.0.5ClCH2CH2Cl, (II) (Jurnak et al., 1975), [Co(CNC6H4Me-p)4I2], (III) (Gilmore et al., 1969), [Co(CNC6H3Et2-2,6)4(ClO4)2], (IV) (Becker & Cooper, 1991), [Co(CNC6H4CO2Me-4)4I2], (V) (Squires & Mayr, 1997), trans-[Co(CNC6H4OSiMe3-2)4I2], (VI) (Hahn & Lügger, 1994), and trans-[Co(CNC6H2iPr2-2,6-4-C≡ CH)4I2], (VII) (Lu et al., 1999). Structural comparisons based on these compounds are shown in Table 1.
The Co—O bond length of 2.245 (2) Å is definitely rather long, since a Co—O single-bond length of about 1.97 Å should be expected (Slade et al., 1971), although this bond is known over the rather wide range of about 1.75–2.40 Å, with 1.85–2.20 Å being most common (Cambridge Structural Database, 2009 [Specific release?]; Allen, 2002). However, the Co—I bonds in (III), (V), (VI) and (VII) are also consistently elongated, while the Co—O bond in (IV), i.e. 2.266 (7) Å, would be considered long, albeit short for a coordinated perchlorate bond. In none of the CoII complexes considered does it appear that the CoC4 moiety is actually square-planar. The CoC4 unit may be planar, having equal [(VII)] or unequal [(IV), (V) or (VI)] Co—C bond lengths, but is also has unequal C—Co—C bond angles, i.e. forming a rectangular plane. Alternatively, as in (III), there is a C2/S4 axis because alternating Co—C bonds are bent above and below the Co centre (~5°). Complex (IV) would appear to approximate most closely the coordination structure for [Co(CNCMe3)4(H2O)2]2+.
Once tetragonal coordination is recognized for (I), analogy with addition complexes of selected nitrogen bases, [Co(CNCMe3)4L2](ClO4)2 (Becker, 1992), becomes apparent. The N-base complexes are blue in colour, due to a crystal field band at 630–670 nm, while (I) is beige to flesh-coloured [Please be more specific - an objective colour is required], with a comparable band at 814 nm. This underscores the higher position in the spectrochemical series of N-ligands over O-ligands (Wulfsberg, 2000). However, the diffuse reflectance electronic spectrum for (IV) (λmax = 875 nm; Becker & Cooper, 1991) is similar to that for (I).
The coordination structure in (I), [Co(CNCMe3)4(H2O)2](ClO4), has thus been shown to be analogous to known [Co(CNR)4X2] complexes with aryl isocyanide ligands. The t-butyl substituents are not seen to be sterically crowded to the extent of precluding coordination of a fifth alkyl isocyanide ligand, and the relatively long Co—O bond lengths contradict the possibility of particularly strong water-molecule coordination, so except for a rather unconvincing argument of strong hydrogen bonding between the coordinated water molecules and the anionic perchlorates, there appears to be no crystallographic explanation as to why a dimeric structure, or at least pentakis-alkyl isocyanide coordination, has not been observed for the title complex.