CCL:G: opt of aluminum complexes

 Sent to CCL by: "Shobe, David" [David.Shobe(a)sud-chemie.com]
 Aleksandra,
 Unless you're using a molecular mechanics method, the coordination
 numbers shouldn't matter.  Perhaps the structure is tricky to draw, but
 it should be possible with a decent front-end.  In particular there
 should be an option to increase the valence of the selected atom; e.g.
 this would change oxygen from divalent to trivalent.
 If that doesn't work, I suppose you can put in nitrogen for the oxygen
 and a transition metal for the aluminium.  But you'd have to remember to
 change them manually later to the correct atoms.
 Your structure probably has a number of unusual (for the organic
 chemist) rings.  Again, your Gaussian front-end program should have a
 means for adding a new bond between 2 selected elements.  For a
 4-membered ring, create the chain A-B-C-D, paying attention to things
 like dihedral angles, and then add a bond between A and D.   You can use
 the "clean structure" option after that, but be prepared to go back to
 the "uncleaned" structure if you don't like the results!
 --David Shobe
 -----Original Message-----
 > From: owner-chemistry~!~ccl.net [mailto:owner-chemistry~!~ccl.net]
 Sent: Thursday, June 28, 2007 12:26 PM
 To: Shobe, David
 Subject: CCL:G: opt of aluminum complexes
 Sent to CCL by: "Aleksandra N Rudnitskaya"
 [Aleksandra.rudnit001=umb.edu]
 Dear CCL members,
 I have a problem with optimization of molecule that contains aluminum,
 oxygen, hydrogen, and silicon. The main problem is that I have a lot of
 doubly bridging oxygen sites. Those bridging bonds are different form
 regular bonds and aluminum, for example, has coordination number 6
 instead of expected 3, or oxygen has coordination number 3 instead of
 usual 2. As fare as I can see, there are two problems, the first, how to
 draw the structure with bridging bonds correctly and, the second, using
 what basis set may I optimize this structure in Gaussian?
 Thank you very much in advance.
 Aleksandrahttp://www.ccl.net/cgi-bin/ccl/send_ccl_messagehttp-:-//www.ccl.net/chemistry/sub_unsub.shtmlhttp-:-//www.ccl.net/spammers.txtThis
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